Lining them up
Since sampling rates and resolutions are so important for sound quality, let's kick things off by quickly seeing how the various audio solutions we'll be testing compare. To make things more interesting, and to add a little perspective, I've also thrown in some information on the number of output channels supported by each card and on the cards' respective prices.
|Internal precision||Hardware channels||Output channels||Price|
|Audio chip||ADC||DAC||DirectSound||DirectSound 3D|
|VIA VT8235/Realtek ALC650||NA||18-bit/48kHz||20-bit/48kHz||NA||NA||5.1||NA|
|Hercules Muse LT||16-bit/48kHz||16||16||4.1||$20|
|Hercules Muse 5.1 DVD||16-bit/48kHz||16||16||5.1||$30|
|Hercules Gamesurround Fortissimo III 7.1||16-bit/48kHz||18-bit/48kHz||20-bit/48kHz||96||52||7.1||$43|
|Hercules Digifire 7.1||16-bit/48kHz||18-bit/48kHz||20-bit/48kHz||96||52||7.1||$80|
|Terratec DMX 6fire 24/96||24-bit/96kHz||32||16||5.1||$250|
A sound card's maximum resolution and sampling rate are often misrepresented by feature tables, marketing literature, and fanboys, but we've got the real dirt on the cards we're testing today. Well, most of the dirt. Determining the actual sampling rates and resolutions of audio and codec chips requires a lot of sifting and digging, but we've uncovered some discrepancies between maximum audio chip and codec ADC/DAC sampling rates and resolutions that need to be mentioned. The big problem here really has more to do with marketing than anything else. Often, an audio card's overall audio quality specs are listed according to the highest resolution and sampling rate offered by either its audio chip or codec. That can be misleading if an audio card's codecs offer higher internal precision than the card's audio chip, since overall audio quality is really dependent on the weakest rather than the strongest link.
Hercules' Gamesurround Fortissimo III and Digifire 7.1 cards suffer from the sampling rate scourge of marketing; their audio chips only have an internal precision of 16 bits at 48kHz, while the card's specs proclaim support for 18/20-bit audio recording/playback at 48kHz. The 18/20-bit audio recording and playback at 48kHz refers to the maximum supported resolutions and sampling rates of the cards' codec chips, but doesn't accurately portray the card's audio precision as a whole. Because an audio solution is only as good as its weakest link, the Fortissimo III and Digifire 7.1 are really only capable of processing 16-bit/48kHz quality audio.
Creative's Audigy is guilty of the same marketing offense as Hercules' Fortissimo III and Digifire 7.1 because of Creative's claim that the Audigy supports 24-bit audio at 96kHz. 24-bit/96kHz audio is indeed supported, but only through the card's DAC. The Audigy's audio chip and ADC are limited to 16-bit audio at 48kHz, which makes them the weakest link.
Hercules' Muses and Terratec's DMX 6fire 24/96 are the only cards to keep sampling rates and resolutions consistent across the audio and codec chips, with the DMX 6fire 24/96 having the best overall internal precision of the lot. Unfortunately, finding out just what sampling rate and resolution VIA's VT8235 south bridge integrated audio uses to process audio internally was beyond the detective skills of this mere mortal. It's probably a safe bet that the VT8235's internal precision doesn't equal the maximum 18/20-bit/48kHz capabilites of the ALC650 codec chip.
Hardware support for DirectSound and DirectSound 3D voices is up next, and there's quite a bit of diversity among the cards. The important spec here is the hardware support for DirectSound 3D voices, which can't be emulated in software. More pedestrian DirectSound mixing can be done in software, so if an application maxes out a card's supported hardware voices, it can always lean on the CPU for help. Since the number of DirectSound voices isn't necessarily limitation for audio playback, I'll let you read those numbers off the chart above. However, hardware DirectSound 3D support deserves a little special attention.
Hercules' Gamesurround Fortissimo III and Digifire 7.1 both support 52 hardware-accelerated DirectSound 3D voices, the most of any sound card in this comparison. Creative's Audigy is up next with its support for 32 hardware-accelerated voices, followed by Hercules' Muse cards and Terratec's DMX 6fire 24/96, which all support only 16 DirectSound 3D voices. While I wouldn't have expected the low-end Muses to have better DirectSound 3D support, it's disappointing to see the DMX 6fire 24/96 wallowing in the mud with them.
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