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Date: Wed, 18 Apr 2001 11:22:45
To: rsgb_lf_group@blacksheep.org
From: "Rik Strobbe" <rik.strobbe@fys.kuleuven.ac.be>
Subject: Re: LF: WOLF test results, soundcard trouble
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>The true sample rates of the soundcard were then measured by other means, 
>they were:
>
>8002.87 samples / second for the DAC (used to transmit)
>7938.09 samples / second for the ADC (used to receive)

One shouldn't expect too much accuracy from the soundcard ADC's. Errors up
to 1% in the sampling rate won't effect their use for games etc... so why
should the manufacturer make them more accurate (and expensive). I wonder
if someone ever tested the linearity, the error will be likely in the same
range.

If we want to go more accurate we either have to calibrate each soundcard
individualy (and hope that there isn't too much drifting) or go to another
device.
A good 16 bit ADC with 'no missing code' and a max. sample rate of 10kHz
and up costs no more than a few $, even high quality 18 or 20 bit ADC's are
available for 10$ or less. So the hardware isn't a real problem. Question
is how to get the data from this ADC into the computer ? 
One way would be to make a plug-in card, but that would :
- require us to open the PC and plug in a card
- require to convince windows that the card is there
- rule out most portable PC's
Another way is tranfer the data via a port into the PC. Most suitable are
either the serial port or the USB port.
Advantage of the serial port is that also the older PC's have it,
disadvantage is the maximum baudrate of 115kB/s (would mean a max. sample
rate of +/-5.5kHz).
The USB port can transfer many MB/s, but isn't available in older PC's.

A well designed external ADC board could solve many of the problems that
occur with the soundcard and shouldn't be too expensive. 
The first question is : is there a 'market' for such a device
A second question : if there is a 'market', are the software developers
willing to adapt their software for such a device.

73, Rik  ON7YD