WOLF test results, soundcard trouble]

[Andre' Kesteloot]

Stewart Nelson wrote:

> Hi all,
>
> Thanks for the interesting posts on frequency errors in sound cards and
> drivers.
>
> It appears that WOLF should use 11025 Hz, rather than 8000 Hz, as its
> standard sample rate.  Upsampling or downsampling by a factor of 4
> should pose no problems for drivers, and I would guess that hardware
> sample rate generators would also be accurate, limited only by the
> oscillator's calibration error and drift.
>
> Version 0.53 can handle 11025 Hz files on receive, but there is currently
> no way to set that value in the .wav header on Tx.  I'll add that feature
> if it will be useful.  Let me know what actual Tx and Rx sample rates
> are seen from your card at 11025 Hz nominal.
>
> Rik's idea of bypassing the card is another good solution.
> One alternative that already exists is the VE2IQ interface.  See
> http://cafe.rapidus.net/bill1/bbs.htm and download SDPCX.ZIP .
> This is a home brew Sigma-Delta A/D which drives a serial port.
> Many PSK and CCW programs can use it, and it has also been used with WOLF.
> You can buy kits from Bill for US$54, or build your own from scratch.
> Sample rate is a precise 7200 Hz.  Resolution is only 8 bits,
> but IMO that is plenty, unless the audio signal is dominated
> by a strong interfering carrier.  If most of the audio power is
> random noise and/or static crashes, then even 1 bit is pretty good!
> Steve VK2ZTO has shown impressive results sampling this way.
>
> If you really need high resolution and linearity, there are several USB
> audio systems on the market.  They offer up to 20 bits at 96 kHz, costing
> ~$150.  I've never tested one, but they are popular in the "semi-pro"
> marketplace, so I would guess that linearity and noise is pretty good.
>
> 73,
>
> Stewart KK7KA