Operation Manual
Thank you for selecting the ZOOM 508 (hereafter simply called the "508"). Please take the time to read this manual carefully so you can get the most out of your 508 and ensure optimum performance and reliability. Retain this manual for future reference. ZOOM CORPORATION
NOAH Bldg., 2-10-2, Miyanishi-cho, Fuchu-shi, Tokyo 183, Japan PHONE: 0423-69-7116 FAX: 0423-69-7115 Printed in Japan 508-5000

1 Major Features

Compact, dedicated delay unit with up to 4000 ms delay time and eight delay types (Four types x two variations). On-board "Zfx-2" DSP (Digital Signal Processor) developed by Zoom, and an innovative design used solely for its delay effects. Achieves superior quality delay sound on a par with high-end devices. You can switch between 24 patches to store diverse settings based on your preference. Seamless function that enables smooth patch transitions without cutting the delay sound when the patch is switched. Ample functions to support powerful live performances, including a hold function for continuing the delay sound until the foot switch is pressed, and a tap function for setting the delay time in the interval between when the foot switch is pressed. Integrated auto-chromatic tuner for guitar. You can tune your insturment easily anywhere, any time. You can also leave the tuning function disabled all the time. The optional FP01 expression pedal enables foot control of the mix level for the delay sound. Dual power supply design allows the unit to be powered from an alkaline battery (6LR61) or an AC adapter.

2 Safety Precautions

USAGE AND SAFETY PRECAUTIONS
In this manual, symbols are used to highlight warnings and cautions for you to read so that accidents can be prevented. The meanings of these symbols are as follows: This symbol indicates explanations about extremely dangerous issues. If users ignore this symbol and handle the device incorrectly, serious injury or death could result. This symbol indicates explanations about dangerous issues. If users ignore this symbol and handle the device the wrong way, bodily injury and damage to the equipment could result.

Usage precautions

Electrical interference
For safety considerations, the 508 has been designed to provide maximum protection against the emission of electromagnetic radiation from inside the device, and from external interference.However, equipment that is very susceptible to interference or that emits powerful electromagnetic waves should not be placed near the 508, as the possibility of interference cannot be ruled out entirely. Whatever the type of digital control device, the 508 included, electromagnetic damage can cause malfunctioning and corrupt or destroy data. Since this is an ever-present danger, thorough care should be taken to minimize the risk of damage.

Warning

Caution
Please observe the following safety tips and precautions to ensure hazard-free use of the 508.

About power

Since power consumption of this unit is fairly high, we recommend the use of an AC adapter whenever possible. When powering the unit from a battery, use only an alkaline type.

Cleaning

Use a soft, dry cloth to clean the 508. If necessary, slightly moisten the cloth. Do not use abrasive cleanser, wax, or solvents (such as paint thinner or cleaning alcohol), since these may dull the finish or damage the surface.

AC adapter operation

Be sure to use only an AC adapter which supplies 9 V DC, 300 mA and is equipped with a "center minus" plug (Zoom AD-0006). The use of an adapter other than the specified type may damage the unit and pose a safety hazard. Connect the AC adapter only to an AC outlet that supplies the rated voltage required by the adapter. When disconnecting the AC adapter from the AC outlet, always grasp the adapter itself and do not pull the cable. If the unit is not to be used for a long time, disconnect the AC adapter from the outlet.
Connecting cables and input and output jacks
You should always turn off the power to the 508 and all other equipment before connecting or disconnecting any cables. Also make sure to disconnect all cables and the AC adapter before moving the 508.

Battery operation

Use only a 9 V (alkaline) battery (6LR61). The 508 cannot be used for recharging. Pay close attention to the labelling of the battery to make sure you choose the correct type. If the 508 is not to be used for an extended period of time, remove the battery from the unit. If battery leakage has occurred, wipe the battery compartment and the battery terminals carefully to remove all remnants of battery fluid. While using the unit, the battery compartment cover should be closed.

Environment

Avoid using your 508 in environments where it will be exposed to: Extreme temperature High humidity or moisture Excessive dust or sand Excessive vibration or shock

Handling

Caution The 508 is a precision instrument. Except for the foot
switches, do not push other parts with your feet or subject them to strong force. Take care that no foreign objects (coins or pins etc.) or liquids enter the unit. Be sure to turn the power to all equipment off before making connections. Before moving the unit, turn the power off and disconnect all cables and the AC adapter.

Alterations

Never open the case of the 508 or attempt to modify the product in any way since this can result in damage to the unit.

7 Selecting Patches

Bank switching
Banks A, b, C, d, E, F are available

BANK F

PATCH DOWN PATCH UP
PATCH 1 PATCH 2 PATCH 3 PATCH 4

Patch switching

24 patches are available

BANK E

PATCH 1 PATCH 2
The 24 patches can be easily selected by pressing the patch pedals. The right patch pedal switches to the next patch and the left patch pedal switches to the previous patch. In the initial condition, the 508 is set up so that the patch pedals select patches continuously, but you can also set up the unit so that patches are switched only within a certain bank of four patches. [For details, see section 9 Patch Switching (Application: Bank Hold ON).] Banks are selected with the VALUE +/keys. Press the VALUE+ key to select the next bank, and the VALUE- key to select the previous bank. For example, to switch from Patch 2, Bank A to Patch 3, Bank C, the patch pedal would have to be pressed nine times. Instead, you can press the VALUE+ key twice to switch to Bank C, and then press the patch pedal (UP) just once to select Patch 3.

PATCH 3 PATCH 4

BANK UP

BANK d

BANK C

BANK DOWN

BANK b

BANK A

Bank/patch switching when Bank Hold is off (initial setting)
8 Using the Bypass/Tuner Mode
The effects of the 508 can be turned off (bypassed) temporarily, so that only the original sound of the instrument is heard. In this mode, the auto-chromatic tuning function via the LED display is also active.

Tuner ON/OFF

Pressing the EDIT key and the STORE key simultaneously for more than one second in Play mode will allow you to select whether or not to activate the tuning function in Bypass mode. When you change the setting, the display will show"tunEr oFF" (tuning function off) or "tunEr on" (tuning function on) according to the setting.

Calibration

Select reference pitch for auto-chromatic guitar tuner (calibration). * The reference pitch (A) can be adjusted in the range from 435 to 445 Hz. When the BANK key is pressed in Bypass/Tuner mode, this is shown as "35" to "45" on the display for a second. Adjust to the suitable value. At power-on, the setting is 440 Hz (40).

Bypass mode

Pressing both patch pedals simultaneously activates the Bypass mode.
Press both pedals together

Bypass ON/OFF

The bypass function is invoked by pressing the left and right patch pedals simultaneously. To cancel the Bypass/Tuner mode, just press one of the patch pedals.
To cancel the Bypass mode, simply press one of the patch pedals. The unit then reverts to the previously selected patch.
Currently selected patch is displayed
Press Release immediately Tuning function (only when the tuning function is ON)

Tuner mode

The 508 is initially set so that the auto-chromatic tuning function for the guitar activates automatically when the Bypass mode is invoked. In Bypass mode, pick an open string to be tuned. The closest note will be shown on the display.
Input signal standby condition

Regular tuning

Do = C Do# = C#

& #w &

4th string &

Re# = D#

& #w
6th string 1st string &

Fa# = F#

3rd string &

w #w w

La = A La# = A#

5th string

& #w & w

Mi = E Fa = F

So = G So# = G#

Re = D

Si = B

2nd string

When the tuning function is active, the parameter cursor LEDs serve as tuning meter, designed to enhance tuning precision during fine adjustments.

Turning tuning function off
If you do not want to activate the tuning function in Bypass Pitch is too high Correctly tuned Pitch is too low mode, press the STORE and EDIT keys simultaneously for more than one second in Play mode. The tuning function will be turned off, and this setting will be stored even when the power is turned off. When you turn the function off, the display will show "tunEr oFF" (tuning function off). To turn the tuning function on, press the same keys simultaneously again. The display will show "tunEr on" (tuning function on).
NOTE: Please note that the tuning function may not operate properly if other effect modules between the guitar and the 508 are on.
3 What Are Banks and Patches?

PATCH

A group of the settings for a certain effect type is called a PATCH. The 508 comes with 24 preset patches which can be changed (edited) by the user.

4 PATCH LIST

The 508 has memory capacity for 24 patches. At the factory, these are programmed with recommended settings. The user can freely change the contents of any patch, and it is also possible to restore the factory settings.

BANK PATCH PATCH NAME

LEAD DELAY SPACY ARPEGGIO SOUND ON SOUND JAZZ CLUB MUTE CUTTING DEEP OLD DELAY ODD METER WARM WRAP DOTTED EIGHT SWEET TONE TRIPLET EDGE DELAY HOLLOW BODY BRIGHT DELAY RHYTHM BOUNCE ETHNIC MY ROOM 150 BPM SHADOW SHORT REVERB HQ DUBBLING 4 SEC DELAY SOFT ECHO COMB FILTER SHORT ECHO

COMMENT

Long delay for lead play Fantastic effect by twin delay Play Brian's harmony Room ambience for jazz guitar Good for muted cutting play Old fashioned echo sound Progressive rock? Warm echo sound Makes dotted eighth note Makes triplet rhythm Enhanced effect Makes acoustic feel sound using comb filter Long delay effect with bright tone Play sixteenth single Imagine Arabian desert Room ambience using stereo echo Playing quarter note makes eighth note 70's echo sound Small reverberation effect Fat doubling effect, good for distortion sound Ultra long delay with much feedback Analog feeling echo sound Intense comb filter effect Short echo sound for global use
The 508 calls up patches in sets of four, called a "bank".
BANK F BANK E BANK d BANK C BANK b BANK A
PATCH 1 PATCH 2 PATCH 3 PATCH 4 PATCH 1 PATCH 2 PATCH 3 PATCH 4 PATCH 1 PATCH 2 PATCH 3 PATCH 4 PATCH 1 PATCH 2 PATCH 3 PATCH 4 PATCH 1 PATCH 2 PATCH 3 PATCH 4 PATCH 1 PATCH 2 PATCH 3 PATCH 4

5 Seamless Function

With conventional delay and multi-effect units, the sound cuts off unnaturally when patches are switched. For example, when switching from a solo performance using a long delay to a patch with a short delay for backing, the delay of the previous patch stops abruptly the instant before the next patch starts, causing the reverberation to sound unnatural. This type of problem experienced by guitarists is solved by the 508's revolutionary seamless function. This function holds the delay sound of the previous patch after it has been switched, so that the transition from one patch to the next is performed smoothly. The seamless function can be used in two ways. One method is to leave the time for the delay sound as it is set in the patch. The other method is to force the delay sound to decrease at the timing decided by the seamless function. It is not necessarily preferable to leave the seamless function on normally. Rather, it should be switched on and off to suit the musical circumstances under which patches are switched. (The on/off status of the seamless function can be stored for each patch.) By combining the seamless and hold functions, you can perform solo by using new patches while holding the riff and rhythm pattern (repeat playback). For details, see [12. Effect Parameters].
Conventional patch switching

Patch is switched

Seamless function

PATCH 1

PATCH 2

Sound is cut

PATCH 1 delay
The delay sound of PATCH 1 overlaps the sound of PATCH 2
6 Controls, Functions and Connections

Front Panel

TUNER indicator
In the 508, this indicator shows that the tuner is active, and it serves as a gauge for fine tuning your instrument.

OUTPUT INPUT

DISPLAY
Displays information required to operate the 508.

Play mode

Displays the selected bank (A-F) and patch (1-4).

Edit mode

Displays the value of the selected effect parameter.
BATTERY EMPTY WARNING display
When the unit is powered from the battery, this indicator begins flashing to warn that the battery is running low.
BANK HOLD DELAY TYPE DELAY TWIN DELAY ECHO TMULTI TAP (x100mS) DLY TIME (x1mS) FEEDBACK TONE

Bypass/Tuner mode

Shows the pitch of the input signal.

STORE key

When the contents of patches are to be stored, this key is used for putting the unit in store standby status and to execute the store function.
TUNER CAL. EDIT VAL. BANK
PARAMETER CURSOR indicator
The status of the DELAY indicator and the SEAMLESS indicator (illuminated, flashing, or off) shows whether the effect module and the Seamless function are on or off respectively.

Setting of direct load function
When the STORE key is pressed for at least 1 second during Play mode (during performance), the direct load function can be switched on or off. [For details, see 10. Patch Switching (Application: Direct Load OFF).]
EFFECT MIX SEAMLESS MODE HOLD/TAP
The status of the DELAY indicator and the SEAMLESS indicator (illuminated or off) shows whether the effect module and the Seamless function are on or off respectively. Also, the effect parameter selected for editing flashes.

DOWN BYPASS

EDIT key (for creating your own patches)
This key serves to toggle between the Play mode and Edit mode (mode for creating patches to suit your taste). In Edit mode, this key can be used to select the effect parameters you wish to change. Also, when the effect parameter HOLD/TAP is selected, press this EDIT key to return from the Edit mode to the Play mode.
Indicators function as tuning meter.

VALUE +/- keys

The keys serve for bank switching.
Setting of bank hold function
When the EDIT key is held down for at least 1 second in Play mode, the bank hold function is turned on or off. [For details, see 9. Patch Switching (Application: Bank Hold ON).]
The keys serve for changing the effect parameter.
The keys serve for setting the tuner reference pitch (calibration).

Rear Panel

PATCH UP (right)/DOWN (left) pedals
The pedals serve for patch switching. Pressing both pedals simultaneously activates the Bypass/Tuner mode.
The pedals serve for selecting effect parameters. Also, when a parameter other than Hold/Tap is currently selected, pressing both pedals simultaneously activates the hold function (for extending the delay sound) and tap function (for setting the delay time in the intervals between pressing the foot switch).
Pressing either pedal cancels the Bypass/Tuner mode to return to Play mode.

INPUT jack

Serves for connecting the guitar. When the unit is powered by the battery, this jack also functions as the power on/off switch. The 508 is powered on by plugging a shielded cable into this jack. When the unit is not in use, the cable should be disconnected to prevent battery drain.

DC IN (AC adapter) jack

Serves for connecting an AC adapter (Zoom AD-0006) which delivers 9 VDC, 300 mA with a "center minus" plug configuration. The 508 is powered on by plugging an AC adapter into this jack.

CONTROL IN jack

When the optional FP01 expression pedal and FS01 foot switch are connected to this jack it can serve as the external control jack. When the optional expression pedal FP01 is connected, it can serve for controlling the mix level of the effect. When the optional foot switch FS01 is connected, chorus can be switched on or off externally.

Hd tp tp A1

In Edit mode, the EDIT key is used for selecting the parameter for editing. Each time the EDIT key is pressed the parameter cursor moves one position down. The flashing position shows which parameter is selected for editing.
(1) Use the EDIT key or patch pedal to select the parameter you wish to change.
(2) Use the VALUE +/- keys to adjust the parameter.
(3) While the eighth parameter cursor LED is flashing, press the EDIT key to return to Play mode.

12 Effect Parameters

Patches in the 508 are called effect parameters, made up of elements that decide the tone. Some effect parameters decide the delay type (delay functions and characteristics), and others decide the delay time and feedback. In compact effectors, the delay type is equivalent to the individual effectors, and the other parameters are equivalent to the control knobs on the effector. This section describes all the effect parameters constituting the patches of the 508.

PARAMETER 1

Selects the delay type. Two variations can be selected for each of DELAY, TWIN DELAY, ECHO, and MULTI TAP DELAY, for a total of eight types.

The setting ranges are

*When types are switched the other parameter settings do not change.

DELAY type

NORMAL DELAY PINGPONG DELAY

TWIN DELAY type

NORMAL TWIN DELAY (MON)

ECHO type

MULTI TAP DELAY type
MULTI TAP DELAY (4 TAPS) MULTI TAP DELAY (6 TAPS)
STEREO TWIN DELAY NORMAL ECHO (MONO) STEREO ECHO

Delay type

Monaural delay enabling extremely long delay of 4000 ms maximum.
Stereo version of NORMAL DELAY. The delay sound is output alternately from the left and right channels.
Twin delay enabling two types of delay having different delay times, Tap 1 (delay time of 4000 ms max.) and Tap 2 (half the delay time of Tap 1). When feedback is set to zero, triple overlay can be achieved (creates the impression that three players are performing).
Stereo version of NORMAL TWIN DELAY. Tap 1 is output to the left channel and Tap 2 to the right channel.
Using a short delay time will create an echo effect similar to reverb, and using a long delay time will create a spacious echo effect you might experience on top of a mountain.

Stereo version of ECHO.

Rhythmical multi-tap delay enabling four types of tap (independent delay).
Multi-tap delay enabling four types of tap.
PARAMETER 2 DELAY TIME (X100 ms) PARAMETER 3 DELAY TIME (X1 ms) PARAMETER 4 FEEDBACK PARAMETER 5

Delay time is set in units of 100 ms. In combination with PARAMETER 3, you can set from 1 ms up to 4000 ms. When you press the +/- keys simultaneously, the value changes in tens -- 10, 20.90, 99. Range of setting
The larger the value, the longer the delay time.
Selection ! change of parameters to
As described in 11. Editing Patches, parameters to be edited are selected by repeatedly pressing the EDIT key, but you can also use the patch pedals for this purpose. Press the PATCH UP pedal (right patch pedal) to move the parameter cursor from the bottom up. Press the PATCH DOWN pedal (left patch pedal) to move the parameter cursor from the top down.
performance will be played back to the end, then the Hold function will be canceled. (The HOLD/TAP indicators will go off.)
Original dry sound Effect sound

Sampling

Delay time is set in units of 1 ms. This parameter is used for fine adjustment of the delay time roughly set with PARAMETER 2. Range of setting
The larger the value, the longer the delay time. When PARAMETER 2 is set to "0", the setting range becomes 1 - 99. When you press the +/- keys simultaneously, the value changes in tens -- 10, 20.90, 99.
Press foot switch Press foot switch Press foot switch (first time) (second time) (third time) Sampling Sampling Sampling Hold function starts canceled
@ Switching effects on and off
Adjusts the feedback of the delay time. Range of setting
The larger the value, the longer the delay time. When you press the +/- keys simultaneously, the value changes in tens -- 10, 20.90, 99.
Normally, the bypass function is used for turning the delay function off during performance. However, a patch should be prepared with the effect turned off if you do not want to use a delay sound with the next patch when using the seamless function to hold the delay sound of the previous patch. To turn the effect off, enter Edit mode and select a parameter other than Hold/Tap, and press the left and right patch pedals simultaneously. This operation turns the effect off, and the parameter cursor LEDs for DELAY TYPE will go off. Further, the display will change as below. Display for effect off when the Delay Type parameter has been selected. Display for effect off when another parameter (except Hold/Tap) has been selected.
Auto mode operation Press the FS01 while playing the guitar, and sampling starts. Sampling ends when the duration of the delay time set for that patch, expires, and playback will begin automatically. (The HOLD/TAP indicator will light up.) When you press the FS01 again, the recording will be played back just one more time to the end and the Hold function will be canceled. (The HOLD/TAP indicator will go off.)

Sampling Delay time

The function of this parameter varies depending on the setting range and the selected delay type. Range of setting

In this range, the function of the parameter varies depending on the delay type selected in PARAMETER 1. When a delay type has been selected Sets the delay sound Hi Damp (effect where the high range is suppressed as the delay repeats). Smaller values result in faster suppression of the high-range delay. When a type other than delay type has been selected Sets the delay sound Hi Cut (smaller values result in the high-range delay is cut).
Press foot switch (first time) Sampling Sampling starts stops Press foot switch (second time) Hold function canceled
To turn the effect on again, enter Edit mode (regardless of the parameter currently selected) and press both patch pedals simultaneously. The parameter setting will return to the original value (the parameter value immediately before being turned off). Also, the effect can be turned off by pressing either of the VALUE +/- keys in Edit mode.
* In Manual mode you may want to set the delay time longer, and in Auto mode set it so that it will match the tempo of the song. *The hold function can be used by pressing the left and right patch pedals simultaneously instead of pressing the FS01. However, for this case, it can be used only in the status selected for the Hold/Tap parameter in Edit mode. * When connecting the FS01, be sure to switch the power off beforehand. Also, if the FS01 is not working as you had expected, switch off the unit and then switch it on again.

Range of setting

# Master level adjustment
PARAMETER 6 EFFECT MIX PARAMETER 7 SEAMLESS MODE
Larger values result in a higher mix level for the delay sound. When you press the +/- keys simultaneously, the value changes in tens -- 10, 20.50.
Adjusts the mix of the delay for the original sound. Range of setting
With the 508 you are also able to set the master effect level that governs the overall effect output level. The master effect level is adjusted in Play mode. Hold the VALUE +/- keys down simultaneously for at least 1 second. The current master level will be displayed for 1 second. While the level is being displayed, use the VALUE +/- keys to change it. The setting range is 0-50. (Default value = 40) The unit does not store the setting for the master effect level. Each time the power is turned on it has to be set again.
The tap function sets the delay time to match the time between when the FS01 is pressed once and then again. This is a handy function for setting the delay time to match the tempo of the music. To use the tap function, the FS01 foot switch must be connected via the CONTROL IN jack. Also, the patch must be selected in advance with the setting tP for the Hold/Tap parameter. Once preparations are complete, press the FS01 and then press it once again within 4 seconds. This operation will set the interval for the delay time of the patch currently selected.

Measuring delay time (valid up to 4 seconds)
Sets the length of the overlap of delay sound by the seamless function when the current patch is switched to a different patch. Range of setting
When the display indicates oF, the seamless function is off. In the range from 0.5 to 10, the time set by this parameter will overlap, regardless of the delay time set in the patch. When the display indicates oo, the delay sound is held for a period of time set in the patch.

Hold function

oF 0.5
The Hold function allows you to press the optional FS01 foot switch to start sampling (recording) the performance, and play back the recording repeatedly until you press the foot switch again. The Hold function has two modes; Manual mode that allows you to specify the end point of sampling using the foot switch, and Auto mode in which the sampling operation is performed for a period of delay time set in the patch. Preparation for using the Hold function To use the Hold function, connect the FS01 foot switch to the CONTROL IN jack. Also, select the patch that has a setting of Hd for the Hold/Tap parameter. Manual mode operation Press the FS01 to start sampling while playing the guitar, and press the FS01 again before the delay time set in the patch expires. The performance made from when you press the FS01 first until when you press it the second time will be sampled and held (played back repeatedly). (The HOLD/TAP indicator will light up.) When you press the FS01 for the third time, the sampled
Press foot switch (first time) Press foot switch (second time)

PARAMETER 8 HOLD/TAP

This parameter is used when the optional FS01 foot switch is connected to the CONTROL IN jack, or when the left and right patch pedals are used to invoke the hold function (for holding the delay sound) or the TAP function (sets the delay time for when the foot switch is pressed). The function used is set for each patch. Range of setting
When the display indicates Hd, the hold function can be used. When the display indicates tP, the tap function can be used.
*If the pedal is not pressed twice within 4 seconds, the setting for the tap function is not valid, and the delay time for the patch will not change. *The tap function can be used by pressing the left and right patch pedals simultaneously instead of pressing the FS01. However, for this case, it can be used only in the status selected for the Hold/Tap parameter in Edit mode. * When connecting the FS01, be sure to switch the power off beforehand. Also, if the FS01 is not working as you had expected, switch off the unit and then switch it on again.

9 Patch Switching (Application: Bank Hold ON)
In the initial setting, the patch pedal switches all patches in order, regardless of the bank divisions. The bank hold function limits switching to the four patches within a bank. When this function is activated, the patch pedals switch in order between the patches in the current bank only. To activate this function, hold the EDIT key down for at least 1 second in Play mode. The BANK HOLD indicator will light. To turn the function off, again hold the EDIT key down for at least 1 second. The BANK HOLD indicator will go off. Banks can be switched using the VALUE +/- keys.

Bank Hold ON

Keeping the EDIT key depressed for at least 1 second activates Bank Hold. To cancel Bank Hold, press the EDIT key again for 1 second.
Banks A, b, C, d, E, F can be switched. PATCH DOWN PATCH UP
4 patches within bank can be switched.
Bank/patch switching when Bank Hold is on

BANK HOLD ON

BANK HOLD OFF
10 Patch Switching (Application: Direct Load OFF)
In the default condition, the 508 is set up in such a way that pressing a patch pedal immediately switches the patch and alters the output sound. This is called Direct Load ON. This switching principle is most convenient when the desired patches are adjacent or close to each other. However, when wanting to switch to a patch that is further away, it may be desirable not to activate the sound of the other patches in between. When this is desired, turn the Direct Load function off as follows. When Direct Load has been turned off, switching banks and patches has no effect until the user confirms the selection.

DIRECT LOAD OFF

Keeping STORE key depressed for 1 second turns Direct Load off. The same procedure serves to turn it on.
For example, when going from patch 1 to patch 4 with Direct Load active, patches 2 and 3 will briefly be heard when the patch UP pedal is pressed three times. When Direct Load is off, pressing the patch UP pedal will change the number on the display (the number flashes), but until the user confirms the choice, the sound remains that of patch 1. To turn Direct Load on or off, keep the STORE key depressed for at least 1 second. To confirm a choice after selecting a patch with Direct Load off, press both patch pedals simultaneously.
Example: Switching from patch 1 to patch 4

BA NK DO WN

PATCH DOWN

PATCH UP

Banks A, b, C, d, E, F can be switched.

Patches can be switched.

Confirming a patch
When display indication flashes, pressing both patch pedals together confirms the patch and switches the output sound.
Patch switching completed Confirm

13 Storing Patches

If you have edited (altered) a patch and turn the 508 off without storing the patch, the patch will revert to its old setting. To store an edited patch, use the following simple procedure. Storing can be carried out in both Play mode and Edit mode. After you have edited the patch, press the STORE key. If the unit is currently in Play mode, release the key before 1 second has elapsed, otherwise the Direct Load function will be activated. The display starts to flash. This condition is called the store standby condition. If you wish, you can abandon the store procedure at this point by pressing the EDIT key. If you press the STORE key once more, the contents of the patch are updated. You can also change the patch number before storing, so that the edited patch will be stored in a different number. In this case, the original patch that was used as a starting point for editing will not be changed.
(2) Press the STORE key. (Unit enters store standby mode.) (4) Press the STORE key once more. (Store process is completed.)
(1) Edit the patch as desired.
(3) Select the patch for storing.

14 Replacing the Battery

If the tuning indicator flashes while the unit is being powered from the battery, the battery is exhausted and should be replaced as described below. Since the 508 has fairly high rated power consumption, use only a 6LRV (alkaline) battery. Using another kind of battery will result in shorter operation.
1. Turn the 508 upside down and open the cover of the battery compartment. (Push the catch to unlock the cover, then lift it up.) 2. Remove the battery from the compartment and disconnect the battery cable. (Grasp the terminal strip and do not pull at the cable.) 3. Connect the battery cable to the new battery, taking care to observe correct polarity (+/-). Then insert the battery into the battery compartment. 4. Close the battery compartment cover, taking care not to pinch the cable. (Make sure that the cover is properly locked.)

6LRV (alkaline) battery

15 Returning Patches to Factory Settings
The 508 comes with 24 predefined patches that have been programmed at the factory. Also after you have edited and stored your own patches, you can return to the factory default settings at any time. This process is called "recalling". Returning all 24 patches to the original contents and resetting the Bank Hold and Direct Load functions is called "all initialize". The Recall mode is separate from the Play mode and Edit mode. You cannot switch directly to Recall mode from these modes. The Recall mode can only be activated by turning the unit on in a special way, as described below. 1. 2. 3. 4. Turn the unit off by disconnecting the AC adapter or the guitar input cable. Keep the STORE key depressed and turn the unit on. The indication "AL" flashes on the display. To perform "all initialize", press the STORE key once more in this condition. The flashing rate increases and the initialization procedure is carried out. When it is completed, the unit automatically enters the Play mode. 5. When wishing to recall only a particular patch, select the patch number in step 3, using the same procedure as for normal patch selection. 6. When the desired patch has been selected, press the STORE key. The flashing rate increases and the contents of the selected patch are recalled. 7. Recalling of individual patches can be carried out continuously. When you wish to terminate the process, press the EDIT key. The unit then returns to the Play mode. Turning the unit off also terminates the recall condition.

16 Specifications

Effects: Special Functions: Banks and Patches: Analog/Digital Conversion: Digital/Analog Conversion: Sampling Frequency: Input: Rated input level: Input impedance: Output: Control Input: Display: Power Requirements: Dimensions: Weight: 8 (4 types x 2 variations) Monaural Delay, Pingpong Delay, Monaural Twin Delay, Stereo Twin Delay, Monaural Echo, Stereo Echo, Multi 4 Tap Delay, Multi 6 Tap Delay Seamless patch change, delay time, tap set, hold delay 6 banks x 4 patches = 24 patches (edit + store possible) 18 bit, 128 times oversampling 16 bit, linear 31.25 kHz Guitar input (standard monaural phone jack) -20 dBm 470 kilohms Combined line/headphone output (standard stereo phone jack) Max. output level: +6 dBm Output load impedance: 10 kilohms or more For optional FP01 or FS01 2-digit, 7-segment LED, tuning indicator, parameter cursor indicator Optional AC adapter 9 VDC, 300 mA (Zoom AD-0006) Battery: 6LRV (alkaline) battery x 1 Battery life: Approx. 4 h continuous operation 147 (W) x 157 (D) x 48 (H) mm 480 g (without batteries)
* 0 dBm = 0.775 Vrms * Design and specifications subject to change without notice.

IEEE COMMUNICATIONS LETTERS, VOL. 9, NO. 6, JUNE 2005
A Delay Model for IEEE 802.11e EDCA
Albert Banchs, Member, IEEE, and Luca Vollero, Member, IEEE
II. D ELAY A NALYSIS Consider a WLAN with a xed number of EDCA stations, each belonging to some AC i, i {1,. , n}. Let ni be the number of stations of AC i and {CWimin , CWimax , AIF Si } the corresponding EDCA parameters. Let us dene mi such that CWimax = 2mi CWimin and Ai such that AIF Si = DIF S + Ai. Let us further dene Sk as the set of ACs with Ai k and N as the largest Ai in the WLAN. In saturation conditions, a station always has a packet available for transmission, and needs to wait for a random backoff time before transmitting it. Let b represent the backoff time counter, and s the number of retransmissions suffered, after a backoff counter decrement of the station. With the assumption of [2] that each transmission attempt collides with a constant and independent probability, it is possible to model the process {b, s} with the same Markov chain as Fig. 5 of [2]. Then, the probability that a station of AC i transmits upon a backoff counter decrement can be computed as [2], i =
2(12pi )(1pR+1 ) i min (1(2p )mi +1 )(1p )+(12p )(1pR+1 )+ CWi i i i i
min 2mi pmi +1 (12p )(1pRmi ) +CWi i i i
Abstract In this letter we present a model to analyze the delay behavior of the EDCA mechanism of IEEE 802.11e. Simulation results validate the accuracy of our analysis. Index Terms WLAN, 802.11e, EDCA, delay analysis.

I. I NTRODUCTION

N this letter we present a model for the backoff delay under saturation conditions of the Enhanced Distributed Channel Access (EDCA) mechanism of the upcoming 802.11e standard [1]. By backoff delay we understand the time elapsed between the start of the backoff process of a packet and its successful transmission. This is one of the main components of the endto-end delay in a WLAN. With saturation conditions we mean that all the stations in the WLAN always have packets to transmit. Note that this corresponds to the worst case and thus provides us with an upper bound of the delay. With EDCA, transmissions are regulated by the following backoff algorithm. Upon starting the backoff process, a station i initializes its backoff time counter to a random value uniformly distributed in the range (0, CWi 1), with CWi initially set to CWimin. The backoff time counter is decremented once every time interval as long as the channel is sensed idle, frozen when a transmission is detected on the channel, and reactivated when the channel is sensed idle again for a period of time equal to AIF Si. The value of is a constant dened by the standard, and AIF Si takes a value of the form DIF S + n, where DIF S is another constant dened by the standard and n is a nonnegative integer. The station transmits when the backoff time counter reaches zero. A collision occurs when two or more stations start transmission simultaneously. After each unsuccessful transmission, CWi is doubled, up to a maximum value CWimax , and the backoff process is restarted. If the number of failed retries reaches a predetermined retry limit R, the packet is discarded. From the above explanation, it can be seen that the behavior of a station depends on a number of congurable parameters (AIF Si , CWimin and CWimax ) that can be set to different values for different Access Categories (ACs). The rest of this letter is devoted to the study of the delay as a function of the number of stations and conguration of each AC.
Manuscript received October 21, 2004. The associate editor coordinating the review of this letter and approving it for publication was Prof. C.-F. Chiasserini. This work was funded in part by the European Communitys Sixth Framework Programme with the IST FP6 Integrated Project DAIDALOS. The work was performed during a visit of L. Vollero funded by the IST FP6 Network of Excellence E-NEXT. Apart from this, the European Commission has no responsibility for the content of this paper. A. Banchs is with the Universidad Carlos III de Madrid, 28911 Madrid, Spain (email: banchs@it.uc3m.es). L. Vollero is with the Universit` degli Studi di Napoli Federico II, 80125 a Naples, Italy (email: vollero@unina.it). Digital Object Identier 10.1109/LCOMM.2005.06015.

where pi is the probability that a transmission attempt of a station of AC i collides. Let us dene a slot time as the time interval between two consecutive backoff counter decrements of a station with minimal AIF Si , i.e. AIF Si = DIF S. We say that the slot time is empty when there is no transmission ongoing on the channel during this interval. Let us further dene a k-slot time as a slot time that is preceded by k or more empty slot times, and let p(ek ) denote the probability that a k-slot time is empty. As a station with Ai = k starts decrementing its backoff counter only after k empty slot times following a nonempty slot time, the backoff counter decrements of this station coincide with the boundaries of the k-slot times. Therefore, a station of AC i, with Ai = k, transmits in a k-slot time with probability i , and does not transmit in any other slot time (see Fig. 1). To compute pi , we use the assumption of [3] that backoff times follow a geometric distribution of parameter i , with which a station of AC i transmits in each k-slot time with an independent probability i. With this assumption, the probability pi that a transmission of a station of AC i collides is equal to the probability that some other station transmits in a k-slot time, and the probability that a k-slot time is empty can be computed as the probability that the considered station does not transmit multiplied by the probability that no other station transmits, p(ek ) = (1 i )(1 pi ) (2)
1089-7798/05$20.00 c 2005 IEEE
BANCHS and VOLLERO: A DELAY MODEL FOR IEEE 802.11E EDCA

nonempty

. nonempty
slot times 0-slot times 1-slot times 2-slot times backoff counter decrements (Ai = 2)
di,j retry 1 previous k,i k,i k,i k,i packet Tinter,tx Tslot Tinter Tslot Bi,0 k-slot times retry j-1 retry j

k,i inter

collision

success

Bi,j k-slot times

Fig. 3.

Average delay in case of j retries.
probability of transmission (Ai = 2)

slot times 2-slot times

Fig. 1.
k-slot times and probability of transmission (example with k = 2).

Tc Tinter,tx

Tslot Tinter k,i =0

Tinter

slot times 1-slot times 2-slot times

Tslot k,i

Fig. 4.
Components of the delay (example with k = 2).
only AC's of set S1 may transmit

2-slot time

transmitted with j retries, respectively,

Fig. 2.

Probability of an empty k-slot time (example with k = 1).

Ptx,i =

(1 pi )pj , Ptx,i,j = (1 pi )pj i i

which yields pi = 1

and di,j is the average delay in case of j retries (see Fig. 3), p(ek ) 1 i (3)

di,j =

k,i k,i k,i Tinter,tx + Bi,l (Tslot + Tinter ) + jTc + Ts (8)

If the previous k-slot time before a given k-slot time is not empty, in this k-slot time only the ACs with Ai k (i.e. the ACs that belong to the set Sk according to our previous denition) may transmit, and, with the above assumption, they transmit with an independent probability i. If the previous k-slot time is empty, the given k-slot time is preceded by k +1 or more empty slot times, which is exactly the denition of (k+1)-slot time, and therefore such a k-slot time is empty with probability p(ek+1 ). Applying this reasoning (see Fig. 2), p(ek ) can be written as p(ek ) = (1 p(ek ))
(1 j )nj + p(ek )p(ek+1 )
k,i where Bi,l is the average backoff time before retry l, Tslot is the average duration of a k-slot time in which the considered k,i k,i station of AC i does not transmit, and Tinter,tx and Tinter are the average duration of the time between two k-slot times when the considered station transmits and does not transmit in the rst one, respectively. Ts and Tc are the average duration of a slot time that contains a success and a collision. Fig. 4 illustrates these delay components under a given sequence of slot times following a collision of the considered station. Expressions to compute Tc and Ts , both for RTS/CTS and no RTS/CTS, are given in [2]. Bi,l is computed as
As (with our denition of N ) in a N -slot time the stations of all ACs may transmit, the following equation holds p(eN ) =

Bi,l =

CWimin 2min(mi ,l) 1 2

(1 j )

k,i Tslot is computed as the sum of probability of success, empty and collision multiplied by the average slot time duration in each case, k,i Tslot = p(sk,i )Ts +p(ek,i )+(1 p(sk,i ) p(ek,i )) Tc (10)
Starting from i i, with (5) we can compute p(eN ). Then, with (4) for k = N 1, we can compute p(eN 1 ). Applying this recursively, we can compute p(ek ) k. Then, from (3) we can compute pi from which we can compute i with (1). We conclude that with the above equations we can express each i as a function of i i, with i {1,. , n}. We therefore have a system of n non-linear equations on the i s that can be resolved using numerical techniques. Once the values i i have been derived, the average backoff delay experienced by a non-dropped packet of a station of AC i, di , is computed as di = 1 Ptx,i
where p(ek,i ) and p(sk,i ) are the probabilities that a kslot time in which the considered station does not transmit1 is empty and contains a success, respectively. We compute p(ek,i ) by applying a similar reasoning to (2), p(ek,i ) = p(ek ) 1 i (11)
and p(sk,i ) by applying the theorem of total probability on the number of empty k-slot times preceding the k-slot time,

Ptx,i,j di,j

p(sk,i ) =
p(ek,i,j )p(sk,i,j ) + p(ek,i,N k ) p(sk,i,N k ) (12)
where Ptx,i and Ptx,i,j are the probabilities that a packet of a station of AC i is not dropped and that it is successfully

1 The condition that the considered station does not transmit holds in the computation of all probabilities until (16).
R = 6, mi = {5, 5, 4, 3} CWimin = {32, 32, 64, 128} , Ai = {0, 2, 2, 4} average delay (ms) ni 16 AC1 Anal. AC2 Anal. AC3 Anal. AC4 Anal. AC1 Sim. AC2 Sim. AC3 Sim. AC4 Sim.

slot times 3-slot times

Tslot k,i,j
Tnext k,i,j =Tinter,tx k,i Tinter k,i,j

Fig. 5.

k,i,j Components of Tinter (example with k = 3 and j = 2).
where p(ek,i,j ) is the probability that a k-slot time is preceded by exactly j empty k-slot times, p(sk,i,j ) is the success probability of such a k-slot time, p(ek,i,N k ) is the probability that a k-slot time is preceded by N k or more empty k-slot times and p(sk,i,N ) the success probability of such a slot time. p(ek,i,j ) corresponds to having a generic k-slot time not empty followed by j empty k-slot times in which, respectively, ACs of sets Sk , Sk+1 ,. , Sj+k1 may transmit,

Fig. 6.

Saturation backoff delay: simulation versus analysis.
k,i,j where Tslot is the average duration of a nonempty slot time preceded by a nonempty k-slot time followed by j empty slot k,i,j times, and Tnext is the average duration between the end of this slot time and the next k-slot time, k,i,j Tslot
p(ek,i,j ) = (1 p(ek,i ))

l=k mSl

(1 m )nm,i

1 Tc +

nm m (1m )nm 1 1

pSp \m

(1p )np

(1m )nm

where nm,i = nm im (the Kronecker function im accounts for the fact that the considered station does not transmit). To compute p(sk,i,j ), we note that, after exactly j empty k-slot times, only the ACs of set Sk+j may transmit, p(sk,i,j ) =
k,i,j k,i Tnext = Tinter,tx

(22) (23)

nl,i l (1 l )nl,i 1

mSk+j \l

(1 m )nm,i (14)
p(ek,i,N k ) and p(sk,i,N ) are computed as follows,
Equations from (18) to (23) form a rst order equation on k,i Tinter,tx , from which we can isolate this term and then derive k,i Tinter , which terminates the analysis. III. S IMULATION R ESULTS

p(ek,i,N k ) = 1

p(ek,i,j )

nl,i 1 mSN \l

p(sk,i,N k ) =

nl,i l (1 l )

(1 m )nm,i (16)
k,i k,i Finally, Tinter and Tinter,tx are computed as k k,i Tinter = (1 p(ek,i )) j=0 k k,i Tinter,tx = j=0 k,i,j p(ek,i,j ) Tinter k,i,j p(ek,i,j ) Tinter
where p(ek,i,j ) is the probability that the interval between a nonempty k-slot time and the next k-slot time starts with k,i,j exactly j empty slot times, and Tinter is the average duration between the two k-slot times in this case. For j = k, p(ek,i,k ) =
k1 k,i,k (1 m )nm , Tinter = k l=0 mSl
We validated the accuracy of our analysis by comparing analytical results against simulations. Fig. 6 gives the average delays, obtained analytically (lines) and via simulation (points), corresponding to 4 ACs. The subplot in the gure gives a zoom of the y-axis for a better observation of the low delays. Experiments are performed for a varying number of stations (ni in the x axis) and mi , CWimin , Ai congurations (given on top of the gure). For all tests, a xed packet length of 1500 bytes, the system parameters of the IEEE 802.11a physical layer and the no RTS/CTS option have been used. We can observe that, for all experiments, analytical results coincide almost exactly with simulations, the error in all cases being well below 1%. We also assessed that the times required to compute the analytical results were very short (a few tenths of ms with a Pentium 4 PC of 2.66 GHz CPU speed). We conclude that the proposed analysis is accurate and computationally efcient. R EFERENCES
[1] Part 11: Wireless LAN Medium Access Control (MAC) and Physical Layer (PHY) specications: Medium Access Control (MAC) Enhancements for Quality of Service (QoS), IEEE Draft Supplement to IEEE Std 802.11, Rev. 802.11e/D9.0, July 2004. [2] H. Wu et al., Performance of reliable transport protocol over IEEE 802.11 wireless LAN: Analysis and enhancement, in Proc. IEEE INFOCOM02, June 2002, pp. 599607. [3] F. Cali, M. Conti, and E. Gregori, Dynamic tuning of the IEEE 802.11 protocol to achieve a theoretical throughput limit, IEEE/ACM Trans. Networking, vol. 8, pp. 785799, Dec. 2000.