[LAD] PCM Troubleshooting Questions

Rory Filer rflyer at gmail.com
Wed Nov 3 21:28:13 UTC 2010

2010/11/3 Jörn Nettingsmeier <nettings at folkwang-hochschule.de>:
> On 10/31/2010 08:51 PM, Rory Filer wrote:
>> I've actually heard _some_ recognizable audio - I could tell it was
>> the song I had selected, but it sounded very distorted (sounded
>> horrible) and I'm certain it wasn't because of a weak FM transmitter
>> signal. I'm guessing it was a mismatch in the formatting of the I2S
>> data between what I was sending and what the FM Tx chip was expecting
>> and that has formed the basis of my troubleshooting effort.
> i think it might be byte ordering... if you swap the lower and the upper
> byte of a 16bit signal, you will get heavy distortion-like noise, but -
> miracle of the human brain - you can still hear some of the audio in the
> mess...
Got the audio working again today and - once again - it sounds horrible.
I checked the byte ordering yesterday by writing a constant into the
PCM output buffer and noting the exact same bit ordering on the data
line monitored by a scope. So, I don't _think_ it's distortion caused by
byte ordering. However I have no experience with what these use cases
actually sound like. I'll try and describe what I'm hearing in case anyone
can offer a suggestion:

The closest I can describe it is it is like listening to a radio
through a really
cheap pair of speakers which are underpowered for the amp driving them.
But there is also a lot of static sound accompanying the voice which seems
to be coming in clusters. The voices are recognizable (I'm listening to talk
radio) so that would suggest the spectrum is intact, no?

Even though I'm using I2S normal mode, it actually sounds a little more
recognizable (but not much better) if I switch to left-justified mode.

Thanks to all for your help and suggestions to now.


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