[mythtv] [mythtv-commits] Ticket #1104: multichannelaudio support

Paul Catchpole paul at paulcatchpole.co.uk
Sun Jan 6 16:14:31 UTC 2008


Mark Spieth wrote:
>> But, I'm seeing the same clipping/conversion-clicking issue that I saw
>> in TV, in mythmusic. TV is still fine. It's the centre channel only
>> again, and seems to happen on any album I pick.
>>
>> Any ideas?
>>     
>
> does the same clipping happen in 2ch mode?
> I had an issue with mad (mp3) in that the audio was distorted (clipped) but 
> no clicking.
> I think it got introduced with the latest upgrade of libmad but not sure.
> I saw it in the stereo wave visualization where the waves went all the way 
> peak to peak with rounding of the peaks which provided the clue.
>
> my fix was the following. note it shouldnt be happening but this is where 
> the clipping occurs.
>
> mark
>
> --- maddecoder.cpp      (revision 15263)
> +++ maddecoder.cpp      (working copy)
> @@ -448,6 +448,7 @@
>  static inline signed long fix_sample(unsigned int bits, mad_fixed_t sample)
>  {
>      mad_fixed_t quantized, check;
> +    sample >>= 1;   // MRS fudge for clipping problem
>      quantized = sample;
>      check = (sample >> MAD_F_FRACBITS) + 1;
>      if (check & ~1) {
>
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>   
Sorry about the delay in testing this, Mark, been a busy week back at work!

It works fine with the audio device for the frontend changed to a 
2-channel one. It's only when using the real 6-channel device and hence 
the upmixer where the clipping occurs.

Is there anything I can do to narrow this down further?

PC


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