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THE LAST ISSUE OF EDN DISSECTED THE PDAUDIO-CF SOUND CARD, WHICH TACKLES DIGITAL-DOMAIN CONVERSIONS. THIS CONCLUDING WRITE-UP DISCUSSES THE OTHER HALF OF THE PDAUDIO-HARDWARE CHAIN, MIC2496, ALONG WITH THE SYSTEM SOFTWARE THAT COMPLETES THE SYMPHONY.
Sound savings: Portable audio recorder takes on tape, part 2
By Brian Dipert, Technical Editor
or users who dont own the necessary analog-centric and analog-to-
digital-conversion gear necessary to transform the signals coming out of their microphones or who want to upgrade
AUDIO PRECISION (dBFS) 80

100 120

their setup to capture high-resolution audio, Core 140 Sound has developed the less-than-$500, dual-chan160 nel Mic2496. Powered by a single 9V battery, 500 1k 2k 5k 10k 20k 40k Mic2496 generates 48V phantom power for the miFREQUENCY RESPONSE (Hz) (a) crophones (if required) and boosts the micro20 phones outputs through an ultra-low-noise preamp 20.5 (Figure 1a). Level-adjustment controls combine with LED-clipping indicators, and the A/D con21 verters deliver sampling rates as high as 96 kHz and 21.5 output their data over both coaxial and opticalS/PDIF connections (Figure 1b). Footprint-com22 AUDIO patible, 192-kHz ADCs, which only recently became PRECISION (dBFS) 22.5 available, will enable Core Sound to develop a higher end unit if demand warrants such a move. 23 Len Moskowitz, the owner of Core Sound, which 23.5 has long catered to the audio-recording communi24 ty, estimates that Mic2496 will run for approximately six hours on a fully charged battery if the mi24.5 crophones are self-powered. Phantom-power draw 25 can reach 10 mA per channel and may notably re500 1k 2k 5k 10k 20k 40k duce the battery-powered operating life. Mic2496 FREQUENCY RESPONSE (Hz) includes both a low-battery LED indication and pro- (b) Mic2496s noise (a) and frequency response (b) curves speak highly of vision for powering via an external ac adapter Figure 1 its capabilities (courtesy Core Sound). or battery pack. In designing Mic2496,

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Figure 2

Moskowitz faced the decision of whether to employ linear voltage regulators, which have low noise but exhibit 40 to 50% efficiency loss, or switching regulators, which have high efficiency but also higher noise than linear alternatives. Core Sound chose a partitioned design that employs both linear and switching-regulator-powered subsystems; the linear portion is for low-draw, high-gain circuits that require a clean power source, and the switching portion is for higher current but more noise-tolerant parts of the design. Moskowitzs technical background both as a staff engineer and as an engineering manager aided him in determining what portions of the PDAudio project he could tackle himself (the architecture definition) and which areas were best left to others (the specifics of the hardware and software design). Un-
willing to hire and directly manage a design team, he submitted a request for proposal to several companies and accepted a quote from Elan Digital Systems, which developed both PDAudio-CF and its WDM (Windows Driver Model) and Pocket PC drivers. The WDM drivers are compatible with a diverse list of Windows 98SE, ME, 2000, and XP audio applications (see sidebar Taking a test-drive). A GLOBAL EFFORT The developers writing Pocket PC-audio applications are Pocco Software from Canada, X-Art in Australia, and US-based PocketREC and Gidluck Mastering, whose Live2496 program Ive written about (Figure 2 and Reference 1). For Linux, programmers from SuSE in Czechoslovakia are doing the driver development, targeting the ALSA (Ad-
Recording software from Gidluck Mastering (a), Pocco Software (b), PocketREC (c) and X-Art (d) lead PDAudios charge into Pocket PC territory.

TAKING A TEST-DRIVE

An audio-recording aficionado, I began my hobby with a Sony TCD-D8 portable DAT (digitalaudio-tape) deck and a set of binaural stealth microphones, but my equipment suite has since expanded. My microphone collection now includes a dual-channel cardioid Audio-Technica AT825 and a set of Oktava MC012s with matched cardioid, hypercardioid, and omnidirectional capsule sets. A Denecke PS-2 portable phantom-power supply powers the microphones, and one of four units amplifies and sometimes also digitizes their signals. These units are a Denecke AD-20, Griffin Technology iMic, Sony SBM-1, and Sound Professionals SP Preamp. The list of options for capturing the audio has also grown from its TCD-D8 foundaF tion (Figure A). I now own a Sony PCM-R300 full-size DAT recorder, along with a Sharp MD-MT15 MiniDisc recorder. My Creative Labs Nomad Jukebox 3 is seeing increasing use, including at last falls Austin City Limits music festival in Austin, TX, and at an EDN editorial meeting in San Francisco during this springs Embedded Systems Conference. When I dont need an ultracompact platform, though, I increasingly turn to a notebook computer, such as my NEC Versa UltraLite, coupled with a Digigram VxPocket sound card and software, such as Sonic Foundrys Sound Forge or Syntrilliums Cool Edit Pro. As such, I bring some expertise to bear on a hands-on evaluation of Core Sounds PDAudio components, which Core Sound owner Len Moskowitz is putting the final polish on before production. PDAudio-CF, which I will couple with my Denecke and Sony-combination microphone preamp and A/D-converter units, will come first. When Mic2496 arrives, Ill do some high-resolution recordings. Regularly visit this sidebar on the Web version of this article at www.edn.com for updates and samples of my results. Ill test the PDAudio system with my notebook PCs, running Windows 2000 and Windows XP Professional, and with my Pocket PC 2002based iPaq 3835. For the Pocket PC, Ive purchased Figure A the iPaq dual-slot PC Card-expansion pack, which embeds two 950-mAhr supplemental batteries and will allow me to simultaneously use PDAudio-CF and a high-density Ive got a plethora of recording PCMCIA or CompactFlash storage options at my disposal. device.

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velopment tools, and the opensource-software community; all have been a significant help during the definition and development stages of PDAudio. In addition to the organizations previously mentioned, other InFigure 3 ternet resources that he and I find particularly helpful include discussion groups, such as DATHeads (www.solorb.com/datheads), Etree (www.etree.org); Laptop-Tapers (http://groups. yahoo.com/groups/laptoptapers), and the Oade Brothers Core Sounds plans extend to forums (www.oade.com/Tapers_ the Linux environment, too. Section); newsgroups such as alt.audio.minidisc and the rec.audio.* family; and Web sites such as Ecasound (www.wakkanet.fi/~kaiv/ ecasound/), Handhelds.org (www.handhelds.org), the Linux Audio Users Guide (www.djcj.org/ LAU/guide/index.php), and Sound and MIDI Software for Linux (http://sound.condorow.net). Reference 1. Dipert, Brian, Software tackles tough times with sound savings, EDN, Sept 5, 2002, pg 20. Authors bio graphy Technical Editor Brian Dipert is looking forward to toting his gear to concerts such as the High Sierra Music Festival and the Seattle Bumbershoot Festival. Contact him at 1-916-454-5242, fax 1-617-558-4470, bdipert@edn.com, and www.bdipert.com.
vanced Linux sound architecture). PDAudio-CF driver source code and a user guide will be freely available to third-party audio-software developers, and Core Sound also plans to open-source the Linux-based PDAudio Recorder application (Figure 3). PDAudio-CF will transfer incoming S/PDIF information at any supported sample rate and size to the system for subsequent processing. Its left to application software to be aware of the system capabilities and limitations and to appropriately handle audio that falls outside those boundaries. Possible actions, dependent on available processing horsepower and also bounded by system-battery-life goals, include rate- and -size-reducing the audio samples or simply displaying an error message that indicates that the user should adjust the operating parameters of the A/D converter before reattempting recording. How much storage space will you need to use the PDAudio system? Dual-channel, 16-bit, 48-kHz recordings require slightly less than 700 Mbytes of storage per hour. Triple that figure for 24-bit, 96kHz audio capture, and double it again for 192-kHzsampled sound. These figures might at first glance seem extravagant, but consider that 512-Mbyte Secure Digital, 1-Gbyte CompactFlash, and 5-Gbyte PCMCIA cards are widely available, and higher density offerings are due to appear by year-end. Manufacturers are also now shipping 60-Gbyte, 2.5-in. hard-disk drives, enhancing the appeal of notebook PCs as high-resolution audio-capture and -editing devices. Moskowitz extols the virtues of Internetbased research, low-cost programmablelogic intellectual-property cores and de-

FOR MORE INFORMATION.

For more information on products such as those discussed in this article, go to www.edn.com and click on the Reader Service link under the Tools & Services section. When you contact any of the following manufacturers directly, please let them know you read about their products in EDN.
Core Sound 1-201-801-0812 www.core-sound.com Enter No. 316 OTHER COMPANIES MENTIONED IN THIS ARTICLE
Elan Digital Systems www.elandigitalsystems.com Gidluck Mastering www.shoptheozarks.com/ GGM Griffin Technology www.griffintechnology.com NEC www.nec.com Kludge Audio www.techwood.org/kludge Oade Brothers www.oade.com
Oktava http://oktava.tula.net Pocco Software www.poccosoftware.com PocketREC www.pocketrec.com Sharp www.sharp-world.com Sonic Foundry www.sonicfoundry.com Sony www.sony.com Sound Professionals www.soundprofessionals.com
SuSE www.suse.com Syntrillium Software www.syntrillium.com X-Art www.x-art.at SUPER INFO NUMBER For more information on the products available from all of the vendors listed in this box, enter no. 317 at www.edn.com/ info.
Audio-Technica www.audio-technica.com Creative Labs www.creative.com Denecke www.denecke.com Digigram www.digigram.com

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