[opus] Issue with decoding 8-bit PCM data

Amit Ashara ashara.amit at gmail.com
Mon Jan 11 09:05:33 PST 2016

Hello Mark,

The resulting 8 bit file has a lot of squelching noise compared to the 16
bit output from OPUS decoder.
During encode I am using

popi16fmtBuffer[ui32Loop] = (opus_int16)pcRdBuf[ui32Loop];

And during decode since the data is in the lower 8 bit I use

pc8bitSamples[ui32Loop] = ((unsigned short)pcop16OutBuf[ui32Loop] ^ 0x80);


On Sat, Jan 9, 2016 at 2:39 PM, Amit Ashara <ashara.amit at gmail.com> wrote:

> Hello Mark,
> Thanks. Let me try the proposed configuration first to make sure that
> linear 8-bit PCM is retrieved.
> Regards
> Amit
> On Sat, Jan 9, 2016 at 12:28 PM, Mark Harris <mark.hsj at gmail.com> wrote:
>> opus_decode() produces 16-bit signed linear PCM, and
>> opus_decode_float() produces 32-bit floating point PCM that is useful
>> when you want a higher bit depth.
>> If you need 8-bit linear PCM then a simple solution would be to use
>> only the top 8 bits of each 16-bit sample from opus_decode().  Note
>> that the WAV format uses unsigned rather than signed integers for
>> 8-bit linear PCM.  (It uses signed for larger sample sizes and AIFF
>> uses signed for all sizes.)  So if you are writing 8-bit linear PCM to
>> WAV then you would need something like (((unsigned short)sample ^
>> 0x8000) >> 8) to convert from signed to unsigned and get the top 8
>> bits of each sample.
>> You will achieve better quality, however, if you apply dither.
>> opusdec applies dither by default if the output is not floating point,
>> although it does not support 8-bit output.
>>  - Mark
>> _______________________________________________
>> opus mailing list
>> opus at xiph.org
>> http://lists.xiph.org/mailman/listinfo/opus
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