[CELT-dev] Bad artifacts at 32kbps

Andrew Lentvorski bsder at allcaps.org
Thu Apr 14 08:35:47 PDT 2011

I have been trying some different sample rate and bitrate combinations 
to get a feel for how CELT behaves.

I then encoded it with a couple of different frame sizes and sample 
rates.  There were some small differences, but nothing horrible.

So, I decided to run with 24KHz sample rate with 16 bit samples.  This 
seemed like a reasonable tradeoff against the quality degradation that 
my folks could perceive.

Then I tried some bitstream rate changes 128Kbps, 64Kbps, and 32Kbps. 
128K and 64K are fine.

32K is *terrible*.  Really, really horrendous.

Is this expected?  Is there a program I can run to estimate the error or 
something?  I expected degradation, but this just falls off a cliff with 
really objectionable artifacts.

My application is going into the embedded space, so I'm quite a bit 
resource conscious.  It's not that I couldn't live with 64kbps, but 
every factor of 2 helps.

By the way, celtenc needs some better error messages.  If you don't 
compile celt with "--enable-custom-modes" (which is no longer the 
default!), trying to figure out why celtenc just errors out no matter 
what you do is maddening.


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