[Lowfer] Re: Soundcard question and...

[Rick Kunath]

Comments inline and snipped as needed...

> Okay, Rick, others,
> Here's specs on a VXpocket Card. Are these among those you suggest for a
> suitable card? (We getting some closure here? )
> 
> • The VXpocket is full duplex, offering simultaneous and independent
> record and playback capabilities.
> • Sampling rates supported are 8, 11.025, 16, 22.05, 24, 32, 44.1, and
> 48 kHz.
> • PCM encoding/decoding rates are 8, 16, or 24 bits.

Missing the lowest sample rate likely to be used, but likely could be 
lived without, and that rate could be re-sampled if re-sampling worked OK.

> • The VXpocket can run applications that comply with Microsoft's WAVE
> protocol.
> • Digigram's Sound Manager driver for Mac OS 8.x makes the flexibility
> and features of these cards available to Apple Macintosh PowerBook
> users.
> • An ASIO driver is also available.
> • When supported by the user application, analog inputs and outputs may
> be configured as one stereo or two mono channels.

Not bad so far... but.

> Let's all realize the compromise inherent using an outboard card such as
> this for sound processing. 1) It's not performing at PCI bus speed, as a
> PC card would or one of the on-board types in a laptop. 2) The owner may
> not have another choice and attempts to make the best of what he owns.
> 3) Just how 'pure' must these sampling rates be for Ham signal work?

As I see it from reading the specs on the PCMCIA card, there are a lot 
of gotchas with this approach. I'm not sure I'd want to try it unless I 
knew for sure I could return it. Additionally, the small physical size 
of the card limits the ability of the manufacturer to select components. 
If it were me, I'd likely go with a well supported USB type card. I 
don't see any glaring advantage to going PCMCIA if PCI isn't an option.

As to sample rates, the *exact* rate isn't that important for DSP 
displays like Spectran, Spectrum Lab, etc. Either of these have the 
option of supplying a correction factor to the application to get the 
actual sample rate to display right on the screen. So no big deal if the 
rate is a little off, it shouldn't be grossly off though. The same goes 
for digital decoding apps, as long as you can supply a correction factor 
to the app, you're all set. The more important thing is that the card's 
clock does not drift all over the place. It will drift a little as it 
warms up after the PC has been off, but should stabilize like a radio 
does after warm up, and stay relatively stable. If it doesn't the 
correction factor needed would drift all over the place, and you'd never 
have it right. The best bet for stability is to ask someone who has a 
card and see what they say, or get one you know you can return after you 
test it.

> But is that among commonly published data or determined empirically by
> died-in-the-wool users?

You basically have to test a card, or know someone who has one and can 
test it for you.

I don't think that PCI based non-motherboard sound cards, or USB type 
external cards are a waste. I always add an after market card to any PC 
I intend doing audio DSP with. A low noise floor and stable clock, along 
with natively supported sample rates goes a long way to better display 
and decoding. And the card does not have to be a high ticket item to get 
good specs. Most of the super expensive stuff is tailored for 
multi-channel playback, something that makes no difference in an audio 
DSP (transmit or receive) application.

Rick Kunath