[SoundStage!]Fringe with Greg Smith
Back Issue Article
January 2000

Hoontech Digital Sound Card, Technics SH-AC500D Surround Decoder

While many audio rules of thumb can become obsolete over time, one truth that's not going away is that digital equipment becomes cheaper and better every year. Right now the DAC chips found in popular consumer electronics are so good that their performance rivals multi-thousand-dollar units from only a few years ago. So when I recently decided that it was about time for a major upgrade in my computer sound card, my first requirement was a digital output that I could connect to regular audio equipment. The benefits of that approach are two-fold. First, this moves the analog circuitry outside of my acoustically and electrically noisy computer case. But even more importantly, it allows me to utilize a more expensive DAC without having the money spent tied up exclusively in the computer. It's a lot easier for me to justify spending $100 on a sound card with digital output and connect it to a $300 DAC, which I could use in another system later, than it is to splurge on a $400 sound card that's of no use without a PC.

For those of you unfamiliar with PC sound cards, a brief history is in order. The market really started to explode when Creative Labs introduced their original Sound Blaster card, which supported 8-bit samples and helped kick off adoption of CD-ROM technology as well. The release of the Sound Blaster 16 card debuted inexpensive, near-CD-quality computer sound with 16 bits of resolution and a 44.1kHz sampling rate. That card is still the lowest-common-denominator standard to which many games are written. Since the Sound Blaster cards were popularized during a period where the ISA bus was the popular interface for add-in cards, a Sound Blaster-compatible card needs to do several things using that older technology spec. The card must respond to a number of different I/O requests on several ports. This typically means a few addresses starting with 0x220 (that's a hexadecimal address) used for the "voice" output that handles digital sound effects, while another set at 0x330 handles MIDI-style instruments emulated with a sampling table located in ROM or RAM. In order to schedule sounds, IRQ 5 and DMA channel 1 are also utilized.

Lately, all the best sound cards are PCI based. These use a considerably more complicated scheme for talking to the card, which generally allows support of the plug-and-play specification for automatic allocation of resources under most operating systems. Such cards often come with Sound Blaster-emulation drivers that map the addresses mentioned above to commands for the PCI bus. Before my recent investigation, the best cheap card of that style I'd found were ones based on the Ensoniq 1370 chipset, which typically sell for $20-$40. After Creative purchased that company, a number of cards based on the inferior 1371 chip were released, and I can't recommend them as highly. It's still possible to find 1370 cards around from some OEM sources. Today, Sound Blaster compatibility isn't nearly as important. Since most new software is written to interface with Microsoft audio standards like Direct Sound, the actual hardware implementation is irrelevant as long as there is a good Windows driver for the card. It's mostly older DOS-based game titles that require SB support.

The requirements I had for my new sound card were pretty straightforward. I wanted a PCI card with a coaxial digital output I could connect to an outboard DAC. The main two sources of cards like this are Creative, whose latest Sound Blaster cards can be outfitted with a digital output, and Turtle Beach. As for software, I wanted drivers for Windows 95, 98, NT, and Linux. I didn't hear much positive press about the quality of the digital out on the Sound Blaster, and at the time it was impossible to get a useful Linux driver. Creative has recently wised up and started supporting that operating system by giving out the technical details necessary to create a driver. As for Turtle Beach, I've tried a couple of their cards before and have been consistently disappointed with the software they provide, especially for less mainstream operating systems.

Just as I was about to give up and buy something expensive to get what I wanted, a tip from uber-geek hangout slashdot.org suggested a new alternative. Trident, best known for making an endless succession of dirt-cheap but decent video cards, had just released a new line of chips for making sound cards. Their 4DWAVE-DX chip powers a wide array of sub-$20 sound cards available from a number of manufacturers, providing most of the latest gee-whiz sound processing features used in modern games at a very reasonable cost. Even more interesting, their 4DWAVE-NX does all that and adds the capability for both TosLink and coaxial digital outputs. And the company had already released everything necessary to write a Linux driver for the card, which is already mature enough for use. Also a helpful input was a 3D Soundsurge Aliens vs. Predator review that discussed using Trident chip for gaming.

The only problem is actually finding a card based on this chipset. If you search the Internet for Trident-based audio cards, the vast majority of what you find will be products using the DX chipset. The main source of cards based on the better NX chips is Hoontech. They're also on the Web with a site hosted in Korea that is sometimes easier to access than the US one. Hoontech sells their cards for around $40 direct through some US e-commerce sites, but I had so many problems accessing them that I certainly wasn't going to throw my credit card at them. Instead I contacted one of their US distributors I know to be reliable, Tracer Technologies, home of the popular DART and DCART programs for cleaning up digitized LPs on your PC. Tracer sells the Hoontech Sound Track Digital 4DWAVE-NX card all ready to go, with the digital outputs mounted on the board, for $49. Tracer was easy to order from, and they delivered my card a few days later without any problems. You're on your own if you try and navigate Hoontech's site to order from them instead. I also found information and drivers for the NX chipset at www.espco.com, which appears to be another OEM that makes boards using it. I have yet to figure out where to buy their cards at, but it's nice to have another source for downloading drivers when I can't get to Hoontech's site in Korea.

The edge of the Hoontech NX looks like a regular sound card. There are mini-jack inputs for a microphone and a line-level source. A joystick/MIDI completes the input ports. Two analog outputs are present, one for the front speakers and one for the rear. The current trend for computer sound cards is to support Microsoft's 3D Sound routines, which output four discrete channels. The digital outputs are located on the rear of the card, which poses a bit of a problem. I connected a 75-ohm RCA video cable to the coax digital output and fed that cord through a random hole in the back of my PC's case. It's also possible that you might break the digital output sub-board off (it's connected to the main card with a cable) and mount that on your case somewhere, like on a customized card slot. I wasn't feeling up for such metal work myself.

There are two basic limitations of the NX chip's digital output. The most obvious is that you can't use any of the 3D sound functions with it. To get more than two channels of digital sound onto a single coaxial output, you need something that will decode that at the other end. This means a surround decoder, and the main standards for such connections are Dolby Digital's AC-3 and DTS. So to output a digital signal from your PC that supports surround, your PC would need to implement AC-3 or DTS encoding, which is not something you get with consumer equipment. Interestingly, there is no technical reason this couldn't happen. For example, DTS runs perfectly fine from a CD player, which outputs a two-channel digital signal. I'd love to see someone release a Direct Sound plug-in that converted all that 3D sound information into a AC-3 or DTS bitstream for connection to real surround equipment. Since some of the titles I like use Dolby Pro-Logic for rear-channel information, I can still get surround sound out of those even through the digital output.

Installation of the card and associated drivers was snap under Windows 95 or 98. An entry is added to the Control Panel that allows you to configure the card. By default, the digital output is disabled, so that's the first thing to change if you plan on hooking up an external DAC. Things didn't go so smoothly under NT 4.0. The driver distributed on the CD Hoontech, labeled V2.2, was missing parts of the control interface, including the ability to enable the S/PDIF digital out. I downloaded a new driver from their website, labeled V4.05.3010, which claimed to fix this problem. Installing that was tricky. NT claimed that since the driver was in use by the system, I couldn't overwrite the files I'd already installed. Undeterred, I removed the driver from the Multimedia part of the Control Panel and rebooted. The OS still claimed the driver files were in use, even though all references to the card I could see were gone. The solution to this was a bit of brute force; I went into the \winnt\system32 directory and deleted all the Trident driver files (trid*.*) there. After rebooting, I was able to install the new driver. If you're using NT, I suggest ignoring the directions on Hoontech's website, which suggest installing the original driver on the CD before applying the update. Instead, add the driver for the card from the website first. When it asks for the gm10mb.slb file, insert the driver CD and point it toward \sound\4dwave-nx\win95. After that bit of trickery, the card worked fine under NT. Most of the other things you can control on the card are related to the 3D-audio functions, including some Q-Sound effects. Since you can only get stereo when using the digital output, I switched the card into two-speaker mode and turned off all the 3D effects.

Next up, I ran some coax cable around to where my DAC and amplifiers are. This brings us to the second major limitation of the Trident NX chipset. Its sampling rate is fixed at 48kHz. You must have a DAC that runs at that speed or you won't be able to use the card's digital output. Most surround decoders support that frequency, as it's used often on DVDs, but some stereo-only digital converters won't support anything higher than 44.1kHz. From a sound-quality perspective, playing back 44.1kHz CD audio files and re-sampling them to 48kHz will definitely lower the sound quality some. In practice, I found the improvements from using an external DAC were so big that any sampling-rate-conversion problems were at worst minor flaws. If you're putting together a world-class audiophile system around this sound card, you might be disappointed when playing CD-rate material. With my modest computer-audio system, I was hard-pressed to tell the difference between playing CD quality .WAV files over the Hoontech card and my Rotel RCC-945 CD changer's digital output.

There are a few glitches in the current state of computer sound with a straight digital output to be aware of. First, cards like the Hoontech may not support changing the master volume or balance control, since those two are often part of the analog output stage. Second, some computer functions that are very CPU or memory intensive can interrupt the sound card's ability to keep the digital bitstream rolling, which results in drop-outs. This is most frequently noted when using video cards that hog the PCI bus; you may be able to adjust this with your video driver or BIOS settings. Finally, and most importantly, many people like to play audio CDs in their computer. If you hook up CD-ROM to the sound card using the usual analog connection, you've just lost much of the potential performance improvement of using a digital sound card. I use a Plextor CD-ROM, which includes software for Windows 98 and late revisions of Windows 95 called AudioFS. This allows Digital Audio Extraction (DAE) from the Plextor drive in real time to the sound card, which keeps the entire signal path inside the computer digital (albeit with a sampling-rate conversion). If you have a different brand of CD-ROM, this won't work for you. I suggest reading up on the workarounds for using a CD-ROM drive with the current crop of USB speakers, which have the same problem -- needing to extract constantly digital audio from a CD-ROM to a digital output device. Two places to start are Microsoft's notes at www.microsoft.com/hwdev/devdes/digitaudio.htm and www.microsoft.com/ hwdev/devdes/cddigital.htm, which suggest some tests you can use on your CD-ROM to see how it handles extraction of digital audio.

Technics SH-AC500D

Surround decoders come in all price ranges. The Lexicon DC-1 I used exclusively for a year was nice in a cost-no-object kind of way, but was clearly excessive for the computer-based system I was trying to put together. Since I listen to both Dolby Digital and DTS recordings regularly, I needed something that would handle both formats, but not cost a whole lot. The Technics SH-AC500D has a few limitations, but it's overall a quite handy piece to have around. Street price on the unit is generally under $300; I got mine for $285 at a local store. It appears the retail price is currently at $350, which is up $50 from when I made my purchase six months ago.

For digital inputs, the AC500D has one TosLink-only port, one coax port, and a third port that can use one of either type. There is also a six-channel line-level input using RCA jacks. For the output of the decoder, there are the usual five surround channels and a subwoofer. Front-panel controls are similarly sparse. You can choose between stereo mode, a surround mode that uses Dolby Digital or Dolby Pro-Logic as appropriate depending on the input source, and DTS. There's no auto switching here; if you don't have the right mode for the source you're trying to get, you'll hear nothing. Setup of the unit involves a somewhat bizarre mix of front-panel buttons and controls on the remote. You can turn off speaker channels you don't have, but there's a limited ability to mix the material in missing channels into the front. Dolby Digital material can be shifted from the center or surround to the main speakers, but DTS requires that all channels be connected. There isn't even support for a phantom center channel in that mode. Bass management is also minimal. Any speaker can be set up as Large, which runs full-range, or Small, which removes bass from that channel below 100Hz and sends that to your subwoofer or main speakers.

Associated Equipment
  • Lexicon DC-1 preamp/DAC/surround processor
  • Rotel 955 Amplifierr
  • Proton D1200 Amplifiers
  • DH Labs BL-1 Interconnects
  • AudioQuest Type 4 and Type 2 Speaker Cable
  • Genesis APM-1 and 750 Speakers
  • ACI B-Flat In-wall speakers

The SH-AC500D is capable of driving power amplifiers directly, and is calibrated so when its volume control is set to 0dB you'll get 2V of output, which is the standard for a normal CD player. So if you're connecting the unit to a receiver or other device with a line-level input, you can keep the Technics volume control at 0dB for best compatibility. I connected the decoder to a variety of amplifiers without any intervening processing, including some older Rotel and Proton units. If your power amp requires more than 2V to reach its full output, you'll need a preamp in the middle to boost the output to that level. Also worth noting is that the line input goes straight through the unit without any change; the volume control doesn't affect it. This effectively makes it impossible to utilize that input and simultaneously drive a power amp directly.

Comparing the sound quality of the SH-AC500D to the Lexicon DC-1 isn't really fair, but I couldn't help but listen anyway. The most obvious flaw of the inexpensive Technics unit is its lack of low-level resolution; subtle details were often lost when playing complicated mixes. It was noticeably harsher on all material, most glaringly films. Compared with the smooth output of the DC-1, less forgiving DVD material like The Fifth Element was more abrasive. But to keep this in proper perspective, this cheap decoder sounded considerably better than the analog output of the circa 1996 Rotel RCC-940AX CD changer I use. On stereo material, the DAC I recall that the SH- AC500D most resembles in sound quality is the CAL Gamma, which sold for about the same amount a few years ago but only handled stereo. With two-channel material, I think the Technics is bettered by the current generation of DVD players; the Pioneer DV-414 I've been playing with recently, which uses 24/96 DACs, has a much clearer top end and smoother overall presentation. If you're buying a new DVD player right now and DTS isn't a big priority, you might be better served getting a model that includes built-in Dolby Digital decoder than buying the Technics decoder. This should only set you back $100 or so, the sound quality will probably be better, and the bass-management features in the DVD player should be equivalent or better.

The main problem Technics SH-AC500D owners are likely to run into is with its poor digital locking. Any digital decoder that handles multiple formats and input frequencies is prone to losing synchronization with the input signal occasionally, which can result in either a brief silence or (as is most frequently encountered with DTS) a burst of noise. Usually this is limited to a fraction of a second when a new disc is first inserted, and an occasional glitch during things like DVD layer changes. On the SH-AC500D, digital lock is lost far more frequently, and for much longer. It's not unusual for the decoder to lose a full second of audio at the beginning of every single track on an audio CD. While this doesn't sound so bad on paper, it's quite annoying in practice. DVDs tend to hold up better, with only the usual clicks between layers and at the beginning of the playback. Using the Hoontech sound card as a source was the worst combination of all. The Trident chipset apparently doesn't transmit anything to the digital output unless there's some signal to propagate, which is good from a noise perspective. The down side is that when you play a short computer sound like the typical "beep" that comes from an error, the sound can frequently start and end before the Technics locks on the signal at all. So short computer sounds never get heard at all.

No, none of this technology is perfect yet. But the Hoontech 4DWAVE-NX sound card is inexpensive enough that I can forgive its few faults, many of which it shares with every digital-output sound card at any cost. The Technics SH-AC500D's locking issues and only adequate sound quality make it a bit harder to recommend unhesitatingly, but it certainly has its place as well.

...Greg Smith


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