Product Review

Behringer DSP8024
Reviewed by Charles Hansen and Bill Fitzmaurice
Behringer Ultra-Curve PRO DSP8024 2Channel Digital Graphic/Parametric Equalizer-Analyzer, Behringer Spezielle Studiotechnik GmbH, Hanns-MartinSchleyer-Strasse 36-38, Willich-Mnchheide II, Germany, +49 (0) 21 54/92 06-0, Fax +49 (0) 21 54/92 06-30, www. behringer.com; list price $230 U.S.; dimensions: 3.5 (89mm) H 19 (483mm) W 12 (305mm) D; net weight: 11 lbs (5kg); warranty 1 year; service available at Behringer USA, Edmonds, Wash.
The DSP8024 is a 24-bit digital audio processor, featuring a real-time analyzer with Auto-Q function for automatic room measurement and correction, a 31-band graphic equalizer, and threeband parametric equalizer. Additional functions include a peak limiter, an adjustable digital delay, a noise gate, and a feedback destroyer feature. Two analog line inputs and one microphone input are provided through XLR and stereo phone jacks. An optional AES8024 feature adds AES/EBU digital inputs/outputs to the DSP8024, but this was not provided with the review unit. You can copy, compare, add, or subtract EQ and analyzer curves, and 100 user memory locations are available. Three level meter references are provided: dBu (dB in reference to 1mW at 600, equal to 0.775V RMS); dBV (dB relative to 1V peak-to-peak); and DIGMAX referenced to maximum output level. If overload occurs, either from excessive analog signal levels or due to digital signal processing limitations, the green LED above the IN/OUT switch turns red. The 36-page users manual is extremely well written, with useful illustrations, examples, and connection diagrams for every application.
PHOTO 1: Front view of unit.
PHOTO 2: Rear view of unit.
TABLE 1 MEASURED PERFORMANCE
PARAMETER Analog input impedance: Max analog input level: Mike input impedance: Mike operating level: Max mike input level: CMRR: Output impedance: Max output level: Frequency response: Signal to noise ratio: THD+N: IMD - CCIF (19+20kHz): Crosstalk: AES/EBU digital input impedance: AES/EBU digital output impedance: Graphic equalizer: Parametric equalizer: Feedback destroyer: Digital delay: Level meter: Noise gate: Limiter: Power requirements: Lithium battery life: MANUFACTURERS RATING 50k balanced 25k unbalanced +21dBu balanced/unbalanced 2k balanced -60dBu to 0dBu +1dBu 40dB typ., >55dB at 1kHz 60 balanced 30 unbalanced +16dBu balanced/unbalanced 20Hz 20kHz, +0/0.5dB 103dB unweighted, 2222kHz 0.004%, 1kHz +4dBu N/S <103dB, 2222kHz 10k balanced, 310Vpp 100 balanced, 5Vpp +16dB to 16dB, 0.5dB steps +16dB to 48dB, 0.5dB steps, 1/60 to 2 octaves bandwidth Down to 48dB, 1/60 to 12/60 octaves bandwidth 0.1ms to 2.5s, each channel 60dB/s RMS, one sample peak, 20dB/s decay Threshold 44dB to 96dB, 1dB steps Threshold 0dB to 36dB, 1dB steps, 500 to 5000ms 30W maximum 3 years typ. MEASURED RESULTS 49k5 balanced 24k9 unbalanced 8.7V RMS (+21dBu) 1k97 balanced 0.87V RMS (+1dBu) 98 balanced 48 unbalanced 4.64V RMS (+15.5dBu) 20Hz 20kHz, +0/0.2dB Below noise floor 0.0039%, 1kHz +4dBu <0.0032% Below noise floor (Not provided) (Not provided) verified verified Not tested Not tested Not tested Not tested

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INSIDE THE EQUALIZER

The Behringer DSP8024 has a black painted steel chassis and 3mm thick aluminum front panel. The unit is designed to be rack-mounted, but you can easily remove the rack supports for shelf mounting. Four adhesive rubber feet are included for this purpose.
BEHRINGER is spelled out in the cooling louvers on the top cover. Photo 1 shows the front panel of the Behringer DSP8024, with its backlit LCD display. The four larger switches on the left control the equalizer (EQ), the real-time analyzer (RTA), signal path IN/OUT switch, and a Setup
key to access menus. The four, smaller vertically oriented switches are softkeys, whose functions change depending on the operating mode. They line up with corresponding pictograms on the display. Four cursor control keys are located in a diamond pattern to the right of the display.

A-2169-1

FIGURE 1: Frequency response.
FIGURE 3: THD+N versus input.

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FIGURE 2: THD+N versus frequency.

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FIGURE 4: THD+N versus output.

A-2169-4

audioXpress February 2003 53
The rear panel (Photo 2) has the IEC power receptacle, with the power switch just above it. The unit is furnished with a heavy power cord. A line fuse is located in a drawer in the IEC receptacle. The third pin of the AC receptacle is connected to the chassis. To the right of the IEC are a number of connectors. A blanking plate covers the cutouts for the AES/EBU digital input/output jacks on the review unit. Just below this plate are MIDI out, through, and input DIN connectors. Next are stereo pairs of analog output
phone jacks and gold male XLR jacks. To their left are stereo pairs of analog input phone jacks and gold female XLR jacks. Finally, there is a gold female XLR mike connector that also provides +15V phantom power. Photo 3 shows the interior of the DSP8024. With the eight cover screws and the cover removed, the side and bottom plates are interlocked with tabin-slot construction that wiggles around quite a bit. The cover provides a fair amount of rigidity, so the unit is solid with the cover in place. You can con-
CRITIQUE: BEHRINGER DIGITAL 8024

By Bill Fitzmaurice

Not so long ago, if you wanted to have a graphic EQ, an RTA, an auto feedback controller, a limiter/noise gate, and a DDL for loudspeaker management, it would have required a rack full of processors. Now, thanks to the digital revolution, you can get all of those toys combined in a single piece of gear, at a price less than any one of those separates might have cost only ten years ago. The generic term for a processor that combines all of those elements is LMS, for Loudspeaker Management System. One such unit is the Behringer Ultra-Curve Pro DSP8024. Behringer is a German company that engineers its products with typical German attention to quality and detail, but avoids Mercedes-like pricing by having its factory in China. With a street price of less than $400, the 8024 offers both versatility and value. When Ed Dell asked me if Id like to review the DSP8024 for audioXpress, it was serendipitous to say the least, since Ive owned a DSP8024 for about a year now. My experience with the 8024 has been almost totally positive, and I wouldnt hesitate to recommend it to anyone looking to upgrade his or her sound system. While intended primarily as a tool for professional sound reinforcement and studio duty, the DSP8024s capabilities may well make it a worthwhile addition to most home stereo systems as well. Why? Because the RTA and EQ features of this two-rack space box can correct the sonic deficiencies inherent in practically any room/speaker combination. WHAT IT CAN DO First, you may use the 8024 as a stereo graphic EQ. It does that job exceedingly well, far better than analog designs, as its digital filters reduce the overlap between EQ bands to negligible. I find the EQ to be very natural sounding, adding no texture of its own to the sonic palette. Claimed S/N ratio is 103dB unweighted, and I have found no reason to doubt that spec. Even with high frequencies boosted to the max, there is no self-noise added, as is the case with analog circuitry. In addition to its dual -octave EQs, the 8024 also offers a pair of three-band shelving filters with user adjustable corner frequencies, and a pair of three-band parametric filters. Whatever EQ chore you want to accomplish, this rig will do it and do it well. Next is the RTA [Real Time Analyzer]. When that function is engaged, the units LCD screen displays a graphic representation of the signal passing through the unit, broken down into -octave bands. You may select the displayed signal from the stereo program input, an external microphone, or onboard generators capable of producing pink noise, white noise, and sine waves. In RTA mode the 8024 can measure everything from speaker response curves to room resonance nodes with dB resolution. One drawback, however, is that while the unit will show you the frequency content of a speakers output, it cannot measure the output level. If you wish to determine a speakers sensitivity as well as its frequency response, youll need a separate dB meter. Perhaps the most useful function, especially for home stereos, is the auto-Q. Hook the 8024 up to your system to play pink noise through your stereo, and it will use the microphone input [Behringer offers a reasonably priced and surprisingly accurate mike for the purpose] to measure the system/room response. The unit then automatically adjusts the graphic EQ for flat response. I use my 8024 in my recording studio for just this purpose, and the difference it makes is quite dramatic, even with accurate speakers in a non-resonant room. The 8024 is even more useful in live sound-reinforcement applications. Auto-Q will appreciably clean up a PA system, especially in the typically poor acoustic environments that most clubs tend to have. Once youve used the auto-Q to get the room/system response flat, you can tweak the individual EQ bands as necessary to fine-tune to your personal preference [since the 8024 will set response flat to 20Hz, its also a good idea to roll off mains response below 60Hz and monitors below 120Hz to protect your speakers and preserve amp headroom]. Having done that, you next engage the Feedback Destroyer function, which uses the parametric filters to search out and destroy microphone feedback. Then you set the output threshold of the limiter, adjustable from 36 to 0dB. This will protect your speakers, and your audiences ears, by limiting how much signal can go into your power amps. Got a noisy PA? Set the noise gate threshold to allow the music through when youre playing a song, but stop the noise when youre in between tunes. If you dont run your PA in stereo, you can split the 8024s two channels, using one to control mains, the other monitors. If you have a really big PA systemand Im talking Woodstock big herethe 8024 has a built-in delay line to adjust the feed to speakers flown over the audience. The only feature lacking is an active crossover, which you probably already have in your rack anyway, and the 8024 costs about a hundred bucks less than LMS processors that include one.

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nect the power transformer on the right for 115V or 230V mains. The beautiful glass epoxy PC board is the picture of digital convergence, looking as though it would be just as much at home in a personal computer. Most of the parts are surface-mount types, including resistors and non-electrolytic caps. The PC board connects to the display and front-panel switches via three ribbon cables.
input to an NJM4580 dual op amp connected as a servo-balanced amplifier. The right input is dedicated, while the left input can select either the left line signal or the mike input. Another 4580 boosts the mike input by +20dB. The StereoLink function can form the two channels into a stereo pair, even if unrelated. The analog stereo signals are then input to an AKM AK5392 24-bit 48kHz
analog-digital converter (ADC). The digital output goes to a pair of TI TMS57002 DSP chips, which are very popular in musical synthesizer effects and computer gaming boards. These DSP chips perform all the gain control, digital filtering, equalization and limiting functions, as well as the digital delay. An Intel 80C31-12 microcontroller running Behringer software stored in a large EPROM handles func-

TOPOLOGY

A schematic was not furnished with the unit, but the manual has a detailed block diagram. Each analog signal is
OPERATION The controls of the 8024 are typical of todays processor-controlled gear in that you use pushbuttons and the LCD display to access its parameter controls. There are no sliders or rotary potsin fact, no knobs at all and unlike analog gear, there is very little about controlling this unit that is intuitive. I figured out how to use the controls with little difficulty, but then I already owned a similarly operated digital console. If this is your first CPU effects box, getting used to the menu scrolling process could be daunting. There is a comprehensive 50-page owners manual, but even getting through that may require the aid of a 12-yearold computer wiz. Unfortunately, this situation is pretty much true with any gear that squeezes as many functions as this one does into such a small package. However, once you set everything the way you want it, you can put everything into memory and store it, with 100 memory locations available. This is most valuable for live-sound work, because you can store the settings for a venue and recall them when you go back for a return engagement, instead of having to reprogram from scratch. The 8024 is MIDI controllable if youre into that, and you may also use its MIDI interface to integrate the 8024 with a computer for both remote control and remote display. For home use you might consider many of the 8024 features to be unnecessary, which is probably true if the auto-Q function is likely all youd want. But if you want to buy a processor that only offers digital EQ and RTA functions, youll likely end up spending just as much. When I bought my 8024 I shopped around for pure RTA/EQ units, found there are very few on the market, and none of them offer a better performance and price value than the 8024. While you may not need its live performance features, youre getting them essentially for free. As to spending about four hundred bucks on an EQ for home stereo, consider this. You can spend thousands on a set of high-end speakers that may give response within 2dB of flat, or you can use auto-Q to achieve near perfect response from even modestly priced speakers, while compensating for room acoustics at the same time. Purists may recoil at the thought of using an RTA/EQ in their system, but the reality of the situation is that many studios today use RTA/EQs, and there is a good chance that a recently produced CD was engineered with an RTA/EQ in the signal chain. Mine was.

PHOTO 3: Interior view.

audioXpress February 2003 55
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tion switching and display control. Lots of high-speed CMOS glue logic is evident on the board. Two Alliance 1MB 4 DRAM chips and a Windbond 32K 8 SRAM chip handle memory requirements. A lithium backup battery maintains the RAM memory when power is turned off. A Dallas DS1210 nonvolatile controller monitors the battery status and writeprotects the RAM contents. The unit always returns to its last used functions when turned back on. Once processed, the analog signals are restored by a Cirrus Logic CS4390 24-bit, 48kHz stereo digital-analog converter (DAC). The DSP8024 has adjustable system sampling rates including 32kHz (AES/EBU only), 44.1kHz, and 48kHz. The default analog signal sampling rate is 48kHz. Digital de-emphasis is provided for 32kHz (AES/EBU only), 44.1kHz, and 48kHz. Finally, the analog signals are connected to the output jacks through their own 4580 servo balanced op-amps circuits. As with the inputs, the output amplifiers maintain the same gain whether balanced or unbalanced output connections are used.
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al AES/EBU digital interface, so testing is limited to the analog inputs and outputs at 48kHz. I found that there was no change in gain going from balanced to unbalanced inputs or outputs. You would normally expect 6dB more gain through the balanced connections, but the DSP8024 servo-balanced output stage detects the type of signal and adjusts the gain accordingly. I ran both channels at 0.5V RMS in, 2V RMS out for one hour into 600. The DSP8024 preserves normal polarity. The tips of the phone jacks and pin 2 of the XLRs are wired hot. You can use a standard mono phone plug as an unbalanced input. The input impedance measured 24k9 unbalanced and 49k5 balanced, independent of volume setting. The output impedances for both channels measured 48 unbalanced and 98 balanced at 1kHz. The DSP8024 showed unity gain when the equalizer and master sliders were all at 0dB. Hum and noise (+16dB gain setting, input shorted) measured 0.18mV, with a DC offset of 0.27mV. Viewing the analog output on an oscilloscope showed only random noise. Relays mute the output during startup and shutdown, and bypass the entire electronics section MEASUREMENTS when you select the OUT mode. The review unit did not have the optionThe frequency response for the DSP8024 is shown in V mV Fig. 1. I made these 3 measurements at a 2 volume setting cor1 responding to 2V RMS output with a -0.5V RMS test signal --(12dB gain), with -0dBr defined as 2V -RMS at 1kHz into -10 100k. It measured -20 0.0 0.2 0.4 0.6 0.8 1.0 1.2 1.4 1.6 1.8 2.0 ms +0/0.2dB from 20Hz to 20kHz. A-2169-5 FIGURE 5: Residual distortion. With a 600 load,

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PHOTO 4: octave RTA screen shot.

56 audioXpress 2/03

the response was down 1.4dB with a slight bit more droop at the low end, possibly due to coupling capacitors in the analog output stages. The mike input showed the same flat response. Its output was actually at 14.9dBr, so I shifted the curve up to 3.7dB to keep it on the graph. HF response rolls off rapidly above 22kHz, where the LP digital filter kicks in. The octave RTA display of my 0.0025% THD 1kHz sine wave test signal is shown in Photo 4. The fundamental is 3dB, with the two adjacent bars (800Hz and 1.25kHz) showing 14.5dB. Crosstalk performance was impeccable, being near the noise floor until 20kHz, where it increased to 90dB. The DSP8024 provides a master gain range of 16dB. Volume control tracking between channels was perfect. When I started measuring distortion, I found the DSP8024 had a somewhat limited range of input/output level combinations where the distortion was below 0.01%. The input voltage clipping point was 8.7V RMS (+21dBu), beyond which the DSP8024 goes into hard brick wall clipping. For any combination of volume setting and input signal level, the output clipping point was always limited to 4.64V RMS. You must take maximum advantage of the input level overhead to keep the distortion low. Low-level analog sources or mikes with low output will tend to produce more output distortion. The least distortion occurs just below where the red digital overload indicator activates. Operating the DSP8024 at the 10dBV consumer reference level will limit the dynamic range much more than the pro-audio +4dBu reference level. The DIGMAX reference level represents the true maximum output level (0dB peak, 3dB RMS). In all cases, the red overload LED signals the start of digital clipping. You should avoid this at all times because it is not harmonic distortion, but rather harsh and objectionable noise. Figure 2 shows the THD+N versus frequency. I engaged the test-set 22kHz low-pass filter to limit the out-of-band noise. The top curve is with a 0.65V RMS input level and +10dBu volume setting, 100k and 600 loads. Next, I intentionally set the input
level to 2V RMS to obtain lower distortion. The middle curve is 0dBu into 600. The bottom curve is at +4dBu with a 600 load. Figure 3 shows THD+N versus input voltage, plotting a 1kHz signal into 600 loads for +12dB, unity gain, and 16dB volume settings. Here you can see the relatively high distortion when input signals are at lower levels. You can also see that output clipping limits the amount of input signal that can be applied. Figure 4 shows THD+N versus output voltage into 100k and 600 loads, using a 1kHz 0.65V RMS input signal. I varied the volume settings to increase the output signal rather than increasing the input signal. Output clipping limits the amount of gain that can be applied. There was very little difference in performance whether I used the master volume slider or the 1kHz EQ slider for gain changes. When I switched the DSP8024 out of the loop, sending the input signal directly to the output connector via the units bypass relays, the THD+N dropped from 0.0042% to 0.0035% (the test set residual THD level is 0.0025%).

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w w w. s i l ve r s o n i c. c o m

dB 100 0.0

kHz 0.2 0.4 0.6 0.8 1.0 1.2

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dB 0 -10 -20 -30 -40 -50 -60 -70 -80 -90 -100 0

kHz 15 20

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FIGURE 6: Spectrum of 50Hz sine wave.
FIGURE 8: Spectrum of 19kHz + 20kHz intermodulation signal.
V 2.0 1.6 1.2 0.8 0.4 0.0 -0.4 -0.8 -1.2 -1.6 -2.0 0.0 0.2

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ms 0.4 0.6 0.8 1.0 1.2 1.4 1.6 1.8 2.0

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FIGURE 7: Spectrum of 1kHz sine wave.
FIGURE 9: 1kHz square-wave response.
The distortion waveform for 2V RMS into 600 at 1kHz is shown in Fig. 5. The upper waveform is the amplifier

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output signal, and the lower waveform is the monitor output (after the THD test-set notch filter), not to scale. This distortion residual signal shows just a bit of high-frequency noise, which is of no significance since THD+N at this point is just 0.0039%. As the input level is reduced this noise increases rapidly. Since data is theoretically processed at 24-bit 48kHz, this suggests either the input ADC or (more likely) the output DAC may not have true 24-bit performance. The spectrum of a 50Hz sine wave at 2V RMS into 600 is shown in Fig. 6, from zero to 1.3kHz. The THD+N measured 0.0042%, with no obvious harmonics present. The only peak above the noise floor is at 60Hz, and this is almost 80dB down. I expanded the spectrum to 20.8kHz using a 1kHz test sine wave (Fig. 7) with similar results. Figure 8 shows the output spectrum when the DSP8024 reproduced a combined 19kHz + 20kHz intermodulation distortion (IMD) signal at 11Vp-p into

600. The 1kHz, 18kHz, and 21kHz products are lost in the noise floor of my test equipment. Repeating the test with a multi-tone IMD signal (9kHz + 10.05kHz + 20kHz, not shown) produced similar results.

SQUARE-WAVE TESTS

The 2Vp-p square wave into 600 at 1kHz (Fig. 9) exhibits the Gibbs phenomenon ringing associated with the steep digital filters used in the DSP section of the DSP8024. For the same reason, the 10kHz square wave (not shown) was rounded over into nearly a sine-wave shape. A 40Hz square wave (also not shown) had very little tilt at 100k load, and only slightly more tilt with a 600 load. During sine testing, as the sine-wave output level increases beyond the initial clipping point, there was an increased amount of this Gibbs phenomenon ringing.
Manufacturers response: The ULTRA-CURVE DSP8024 represents digital mainframe technology at its best. Some remarkable engineering went into the design of the unit. The impressive result is an all-in-one professional equalizing solution for live, studio, and even home stereo system applicationsyet it retails at a price thats
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more consumer electronics than typically pro audio oriented. The ULTRA-CURVEs digital 24-bit dualDSP mainframe architecture is based on two extremely powerful, high-speed DSPs, firstclass 24-bit A/D and D/A converters from either CIRRUS LOGIC or CRYSTAL, ensuring impressive specs that were nicely underscored by the reviews meticulous test results. With its broad range of functions and outstanding audio quality, the ULTRA-CURVE PRO DSP8024 is ideally suited for demanding users and applications. Left to mention is the relay-controlled hard bypass with auto bypass function that guarantees uninterrupted operation in case of power failure. No matter what your application, the ULTRACURVE PRO puts you in total command. For example, Scott Schenk, monitor engineer for Dwight Yoakam, Smashmouth, Third Eye Blind, and others, likes the DSP8024 because it provides him with perfect control over individual signals. For Scott, the equalizer is also top-notch for in-ears, parametric and third-octave equalization, while the units limiter and delay enable him to line up his musicians in-ears with monitor speakers. In order to keep up with the fast pace of technological progress, the 8024 features an open architecture for easy software updates. Free Windows editor software and a new firmware release v. 1.3 is downloadable from the BEHRINGER website. For those who prefer a more purist equalization approach, the TUBE ULTRA-Q T1951 24-band parametric tube equalizer with 12AX7 vacuum tubes and BEHRINGERs trademark ULTRA-TUBE circuitry technology may be the solution. BEHRINGERs range of equalizers currently embraces four parametric and graphic tube and solid-state equalizers. Torsten M. Notzke BEHRINGER Public Relations

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