Peter,
One subtlety that was mentioned once but not emphasized very much is
that some of what you may be seeing as "noise" is actually deliberate
dithering in the card, which has the effect of pushing quantization
noise out to inaudible frequencies. 8-bits seems a bit much for
dithering to me, but still, a "perfect" non-dithering card, i.e., one
that outputs a pure string of '0's for a shorted input, is arguably
_worse_ than a dithering card that outputs a controlled spectrum of
noise on shorted input. It can all get rather weird when there are
non-linear, low S/S+N psychoacoustic detectors at the end of the chain,
i.e., ears.
Chris - AE6VK
-----Original Message-----
From: Peter Martinez [mailto:[EMAIL PROTECTED]
Sent: Friday, May 19, 2006 11:20 PM
To: Flex Reflector
Subject: Re: [Flexradio] 16 versus 24 bit audio
>From G3PLX:
Alberto: Thanks! That's the information I was seeking. It looks as if
I
was half-right, if there are, at best, 18 good bits in a 24-bit card. As
Phil says, if 16-bit cards turn out to be worse that 16-bits, then there
is
some reason to go for a 24-bit card (which is worse than 24bits!). But
for
sure, 24 bit cards are not going to be 256-times (48dB, 8-bits) better
than
16-bit cards.
I will now continue working to convert my own 16-bit SDR code to
24-bits,
but I think I will add a button on the front panel which zaps the bottom
8
bits. It will be VERY interesting to see if it makes any difference. To
take
Frank's point, as far as I can see from both the ASIO and WMME
interfaces,
there IS an accessible point in the software where this can be done
before
the audio data becomes floating-point.
Thanks to all who replied.
73
Peter
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