h5100 h5400 h5500 8KHz audio

Hi,
  This message is kind of a continuation of a thread called "VoIP Sample
Rate" and "audio sample rate" from Jan19-25, 2005.

  I've been tinkering with the h5400 audio (OSS drivers and familiar 0.8
distribution) for the last week or so. I've been experimenting and
"peeling the onion" removing all the patches/fixes in pxa-i2s.c,
pxa-audio.c and h5400-audio.c that compensate for the problem with the 8KHz
sampling rate and, as near as I can tell, there is no problem at all with
the 8KHz sampling rate.

  I've been trying out all the combinations of settings and software fixes,
and I have to agree with Manu Sharma's Jan 25 posting -- there just seems
to be no fundamental problem! Both the ak4535 and PXA255 work in 256fs
mode. It is true that the spec claims 4dB more noise operating in this
mode; but like Sharma said, it is 84dB SNR in this mode versus 88dB in the
other modes -- not enough to make a major difference.

  For me the noise level was only a problem when I had the MIC gain set too
high. When the gain is turned down so that the input isn't distorted, the
MIC input sound beautiful and the background noise is not noticeable. The
8KHz output side is beautiful, too.

  Quality with voice input is just fine. I also tested this out with some
audio test gear generating pure sinewave tones as input and looking at the
outputs on a spectrum analyzer. There are only hints of distortion when
MIC/Speaker gains are set too high, which is to be expected. There are
only problems with 8KHz audio when the hardware is set to something other
than 256fs and SADIV_BITCLK_512_00_KHZ.

  Unless there is some ongoing discussion or evidence to why this isn't the
case, I'll post a patch removing all of the 8KHz work-arounds tomorrow.

Jim

-- 
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James T. Kaba                   
Sarnoff Corporation   There are 10 kinds of people in the world:
jkaba_at_sarnoff.com     those who understand binary, and those who don't.
609-734-2246