[RichD]

On Apr 22, Tim Little wrote:
I was listening to a talk where the speaker put on a Jazz song with
at least a 13-member band (lots of instruments). *He stated, not
that song has some entropy. *This confused me as the song did have a
lot instruments, but was very clear, not full of noise and enjoyable.

Entropy can be characterized as unpredictability. *Sure, a totally
chaotic mess would be more unpredictable, but I would expect
a 13 member jazz band to be more unpredictable than many other
examples of music.

Yes, he meant its complexity, relative to pop.

Claude Shannon estimated music at 40 bits/sec entropy.
What does MP3 achieve?

--
Rich

[Joel Koltner]

"RichD" wrote in message
...
Claude Shannon estimated music at 40 bits/sec entropy.
What does MP3 achieve?

It's an apples and oranges comparison: Claude there is talking about how many
bits of information the musicians need to know what to play, but it's assumed
they already know how to proficiently play their instruments as part of an
orchestra, which is itself a MASSIVE amount of information. MP3 has nowhere
near as much already-known ("dictionary") information. Indeed, about the only
thing that MP3 "knows" at all is how the human ear behaves in terms of masking
behavior, and hence has a pretty good idea as to what of the "raw audio bits"
it takes in can be safely thrown away without anyone noticing too much.
(...and some early MP3 encoder didn't even know much about that... :-) )

A better comparison would be with a speech encoder such as Speex: Speech
encoders typically model the physics of the human vocal tract, and therefore
can often get away with upwards of an order of magnitude less bandwidth
(bits/sec) for a given quality of speech relative to something like MP3.
....but they tend to fall apart completely if asked to reproduce something
other than human speech, such as music (...just as, e.g., a flute can never
sounds like a saxophone...).

---Joel

[RichD]

On Apr 22, "Joel Koltner" wrote:
Claude Shannon estimated music at 40 bits/sec entropy.
What does MP3 achieve?

It's an apples and oranges comparison: Claude there is talking
about how many bits of information the musicians need to
know what to play, but it's assumed they already know how
to proficiently play their instruments as part of an orchestra,

No, he wasn't.
Evidently you don't understand Shannon entropy.

Indeed, about the only thing that MP3 "knows" at all is how the
human ear behaves in terms of masking
behavior, and hence has a pretty good idea as to what of the
"raw audio bits" it takes in can be safely thrown away without
anyone noticing too much.

A better comparison would be with a speech encoder such as Speex:
Speech encoders typically model the physics of the human vocal
tract, and therefore can often get away with upwards of an order of
magnitude less bandwidth
(bits/sec) for a given quality of speech relative to something like MP3.

Then the speech playback decoder generates
sound through a model of the human vocal tract?
Very impressive, if true -

--
Rich

[Tim Little]

On 2011-04-22, RichD wrote:
Claude Shannon estimated music at 40 bits/sec entropy. What does
MP3 achieve?

MP3 bitrate is a tunable parameter, though it doesn't go as low as
40 bits/s. In fact MP3 typically has about 40 frames per second, and a
frame header requires a lot more than 1 bit.

However, the format encodes a *lot* more than a musical score. Every
note from an instrument in a performance is different, and people can
hear many of those differences. A performance compressed to 40 bit/s
would be much more regular and "mechanical" than any real performance.


Still, it is true that MP3 is poor at compressing very similar sounds
that are temporally separated. Frames are mostly independent of one
another, so that even most short-range temporal structure is
completely ignored.


--
Tim

[Tim Little]

On 2011-04-22, RichD wrote:
No, he wasn't. Evidently you don't understand Shannon entropy.

Shannon did quite a lot of work on entropy of music. Which particular
work are you citing with your quote of 40 bits/s?


Then the speech playback decoder generates sound through a model of
the human vocal tract? Very impressive, if true -

A mathematical model, yes. Such models do usually have more free
parameters than any human can achieve, but close enough to allow very
substantial compression ratios.


--
Tim