[CELT-dev] Artifacts in One Channel of Stereo C55x Implementation

Bob Bang bob.bang2 at gmail.com
Thu Feb 3 06:51:00 PST 2011

Yes, the integer overflow was my first thought as well. I tested the the
code on a PC with the "celtenc" and "celtdec" exe's.  I assume if I
configured the compilation with "--enable-fixed-point" that the behavior
would manifest itself. It did not, so it may be an issue specific to the
DSP. I can try to track this down, or I may upgrade the CELT revision. What
revision contains the newer constraint on frame size? (The prime factors of
2,3 & 5) My system is quite defined on a 100 sample frame size so obviously
that newer constraint won't work.

Also, in debugging my system I have seen that for a static frame input to
the encoder, I see the exact same encoded buffer output , byte for byte,
every call. Is this expected behavior? Is there no state information passed
along to the decoder in the compressed buffer? So basically, for every input
X[n], there is a defined output Y[n]?

thanks for getting back to me, I appreciate the help and love what you're
doing here.

On Mon, Jan 31, 2011 at 9:46 PM, Jean-Marc Valin <jmvalin at jmvalin.ca> wrote:

> I guess the first question is whether you can reproduce the problem on a PC
> with the same code. If not, then the most likely issue is a 16-bit integer
> overflow. CELT *attmpts* to only use the "int" type for values that won't
> overflow a 16-bit int. However, because we have no 16-bit platform to test,
> it's likely that we missed something.
> Cheers,
>        Jean-Marc
> On 11-01-31 03:34 PM, Bob Bang wrote:
>> Hi guys,
>> I am on a C55x stereo implementation of CELT 0.7.1; I am using 100
>> sample frame size and writing 58 Bytes per Packet. At the output of the
>> decoder I see one channel reconstructed perfectly, but the other channel
>> has random corruption that appears to be a sinusoid with a period of the
>> frame size.  The artifact is non-periodic and appears to happen randomly
>> during the audio stream.
>> Anyone ever run across this? Have any insight?
>> thanks
>> _______________________________________________
>> celt-dev mailing list
>> celt-dev at xiph.org
>> http://lists.xiph.org/mailman/listinfo/celt-dev
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