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

Paul Catchpole paul at paulcatchpole.co.uk
Sun Jan 6 23:11:50 UTC 2008


Paul Catchpole wrote:
> 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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>   
Also, as an aside, setting the frontend to the 2-channel device on this 
patch-40 frontend caused very, very quiet sound in Live TV and 
Recordings - although it might have been caused by something odd with my 
setup here. The sound I could here sounded rather odd and distorted too.

PC


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