[Lowfer] Re: Soundcard question and...

[Rick Kunath]

Peter Barick wrote:
> For the on-going soundcard matter--harrump--now saga...
> 

<Snipped>

> Here's some specs from Creative Labs and their Sound Blaster application for a PCMCIA add-on.
> 
> It's for their S-B Audigy-2 Z5 CardBus version.
> Playback: 24-bit Digital-to-Analog conversion of digital sources at 96 kHz to analog 7.1 speaker output,
> 192kHz for Stereo DVD-A 

No mention of sampling rates supported for playback, likely not any 
under 44.1 KHz.

> Recording: 24-bit Analog-to-Digital conversion of stereo analog inputs at 96 kHz sample rate 
> Supports Sony/Philips Digital Interface (SPDIF) format of up to 24-bit/96 kHz quality at selectable sampling
> rate of 44.1, 48 or 96 kHz

Again, no input sampling rates supported below 44.1 KHz.

Many audio DSP radio related applications expect the sound card to 
support sampling rates as low as 5512 Hz, 8000 Hz, 11,025 Hz, and 22,050 
Hz, in addition to 44.1 KHz and 48 Khz.

This card does not natively support these sample slower rates, so 
re-sampling will have to be done when sample rates slower than 44.1 KHz 
are used. And this will be a lot of the time on audio DSP apps.

One of the most important things to look at is supported sample rates on 
a card you want to use for audio DSP purposes. This one isn't the best 
choice because of it's limited set of natively supported sampling rates.

In addition to fully supported sampling rates, on-board clock stability 
is important to an audio card. Some of the DSP modes require a stable 
audio card on-board clock so that the actual sampling rate remains 
constant. Being close to the stated sample rate in important, but this 
can generally be corrected with a correction factor entered into the 
apps setup screen. If the card drifts a lot, clock speed wise, it isn't 
going to maintain the expected sample rate exactly, or hold the entered 
correction factor, and DSP performance will suffer.

Additionally, any USB based card is already at a disadvantage because it 
does not have direct memory access or direct microprocessor interrupt 
access like a PCI card does. If you're trying for really low latency, 
this is a problem.

Rick Kunath