[ghost-dev] Quantization of sine params

[Anup K C]

Hi Jean-Marc

This is what I have been trying.

Frequency quantization
----------------------
Based on the methods mentioned in those references, the following is a kind
of scheme that does seem to depict the sinusoids appearing in a generic
music stream.

1. Group the sinusoids in each frame as
{F1,2*F1,3*F1,4*F1,...},{F2,2*F2,3*F2,4*F2,...} and so on. So this takes
care of the harmonic nature of the sinusoids.
2. Compare the groups for the current frame with the groups used for the
previous frame. If there is a new group appearing send it. If there are some
haromonics added or removed from the groups for previous frame send that as
well. Else don't send any new information to the decoder. Also take care of
the situation where a group in the current frame is
{(F1+f),2*(F1+f),3*(F1+f),4*(F1+f),...}. But in most of the cases it has
been found that it is better to start sending a new group altogether rather
than sending these shifts (f).

Problems faced for this model: The harmonics do not fit into a simplisitc
model of (n*F1). it is rather (n*F1+f) is some cases. I guess we will have
to have the key-frame concepts here to avoid inter-frame dependencies, as
you suggested.

As of now I am testing this model based on how frequently I have to send
extra information to teh decoder.

Amplitude Quantization
----------------------
I was trying to obtain some patterns for the amplitude deviations for each
sine component. But could not really see a pattern like exponential decay in
most cases. Except for the obvious time-differential coding I could not try
anything else. I am kind of unsure about how to go ahead here.

As for quantization I have not done anything yet.

Other methods tried:
-------------------
1. Sorting. Does not seem to yield much. As you pointed out, just for the
sake of amplitude quantization the pattern of appearance of sinusoids is
sacrificed here. So not much progress with this
2. Quantize frequencies of a few selected sinusoids and recreate other
values using interpolation: Idea was to sampe the frequency curve in each
frame and send only a few selected tones to the decoder. th rest of the
tones will be obtained using interpolation from them. But the harmonic
grouping seem to work better than this.

Still to be tried
---------------
1. Removal of non-perceptible sinusoids based on psych model.
PS: I didnt quite get what you meant by encode-simulation.

-Anup
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