[Speex-dev] Quality vs. Bitrate vs. Complexity

Randy Yates yates at ieee.org
Sat Apr 3 20:56:40 PDT 2010

Jean-Marc Valin <jean-marc.valin at usherbrooke.ca> writes:

> On 2010-04-03 22:52, Randy Yates wrote:
>> Jean-Marc Valin<jean-marc.valin at usherbrooke.ca>  writes:
>>> Quality and bit-rate are different ways of specifying exactly the same
>>> thing. Complexity is orthogonal.
>> That clears it up - thanks. Is this in the manual?
> Have a look and tell me.


In your 1.2 Beta 3 manual, on p. 7, you discuss quality: 

  Quality (variable)
  Speex is a lossy codec, which means that it achives compression at the
  expense of fidelity of the input speech signal. Unlike some other
  speech codecs, it is possible to control the tradeoff made between
  quality and bit-rate. The Speex encoding process is controlled most of
  the time by a quality parameter that ranges from 0 to 10. In constant
  bit-rate (CBR) operation, the quality parameter is an integer, while
  for variable bit-rate (VBR), the parameter is a float.

The sentence "Unlike some other speech codecs, it is possible to control
the tradeoff made between quality and bit-rate" implies to me that they
are NOT the same thing.

So, while you do discuss these terms in your manual, what you state
there seems to contradict what you've stated here in this mailing list.


> 	Jean-Marc
>> --Randy
>>> 	Jean-Marc
>>> On 2010-04-03 08:28, Randy Yates wrote:
>>>> Jean-Marc: I know you're seeing these - how about a response?
>>>> --Randy
>>>> Randy Yates<yates at ieee.org>   writes:
>>>>> If I understand these terms correctly, you cannot specify simultaneously
>>>>> all three, e.g., high quality, low bitrate, and low complexity.
>>>>> It seems that specifying any two implies the third.  For example,
>>>>> specifying a high quality and low bitrate will necessarily require a
>>>>> high complexity.
>>>>> Am I correct? If not, can someone please explain how these parameters
>>>>> interact?
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Randy Yates                      % "Bird, on the wing,
Digital Signal Labs              %   goes floating by
mailto://yates@ieee.org          %   but there's a teardrop in his eye..."
http://www.digitalsignallabs.com % 'One Summer Dream', *Face The Music*, ELO

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