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Old 03 March 2009, 11:37 pm   #1
dev
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Default What is that?

Hi

I have no doubts about Musepack quality i`m just curious as to why and what for there is added constant sinwave on actual sound.
Test file sweep 50-22000 Hz



Can somebody please explain this to me.
thx
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Old 04 March 2009, 01:18 am   #2
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1. your "graphs" are undetailed, to say the least.

2. it can't be simply explained in one sentence or even many. You should learn how various forms of audio processing, and specifically, audio coding formats work if you want to understand exactly what you can see in graphs.

3. In short, with a sine wave sweep, more than with any other audio content, you will see lots of interesting "artifacts" when you apply any form of audio processing. Be it dividing the audio into bands (as Musepack does, among many other things), applying simple filtering, various forms of FFT processing, resampling, etc. etc.
What you see in a graph (and especially one of a processed pure sine wave), doesn't necessarily reflect what you hear.

Suggestion: try to generate a sawtooth tone or sweep, then look closely and ask yourself how come while what you're hearing is a sawtooth wave, the actual graphical representation of it looks more like a swirly ramp.
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Old 04 March 2009, 08:22 am   #3
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Quote:
Originally Posted by Shy View Post
1. your "graphs" are undetailed, to say the least.

2. it can't be simply explained in one sentence or even many. You should learn how various forms of audio processing, and specifically, audio coding formats work if you want to understand exactly what you can see in graphs.

3. In short, with a sine wave sweep, more than with any other audio content, you will see lots of interesting "artifacts" when you apply any form of audio processing. Be it dividing the audio into bands (as Musepack does, among many other things), applying simple filtering, various forms of FFT processing, resampling, etc. etc.
What you see in a graph (and especially one of a processed pure sine wave), doesn't necessarily reflect what you hear.

Suggestion: try to generate a sawtooth tone or sweep, then look closely and ask yourself how come while what you're hearing is a sawtooth wave, the actual graphical representation of it looks more like a swirly ramp.

1. Yes, I wanted to put it simply, but to correct that; on my spectrum analizer original PCM is shown above, the "Musepack" graphs, I wanted to show that added sinwave in slideshow, as it goes from left to right and gets biger... .

2. Problem is that there is not much specification on Musepack from what I could find, and from technical point of view I`m intreested as to why this sinvawe goes louder and louder as sweep goes up on frequency, I`m not asking as "why the hell it`s there? :evil: ", simply what for what that gives, some ath, noise normalization... ?

3. "What you see in a graph (and especially one of a processed pure sine wave), doesn't necessarily reflect what you hear." - I know they don`t
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Old 04 March 2009, 09:32 am   #4
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Coming from me or anyone with little knowledge, the answers to why it increases as the frequency of the sine sweep rises could be many, neither of which is accurate. I'm sorry, but any answer I give can only be very partially accurate, as I can only refer to parts that make up Musepack's analysis and synthesis and not the sum of the parts (in essence the entire audio coder, psychoacoustic model and all, which you have to be very knowledgable to understand), which is the only thing to refer to if you want a real, accurate answer.

You may find a detailed specification of MPEG-1 Layer 2 coding tools and start from there. Musepack was based on it, and extended with various own tools/psymodel. It includes subband-based selectable channel coupling (search channel coupling info), adaptive noise shaping (or "ANS". various info available as well), clear voice detection (no info. basically, it helps the psymodel perform better during changes of the base frequency of harmonic signals). The spreading function that depends on the mid frequency and sound pressure level of critical bands is non-linear. Temporal masking with a variable time constant is used.

To give a superficial answer: it's probably related to the way the psychoacoustic model treats audio differently at different frequencies, the nature of polyphase quadrature filters, and maybe as high as 5th order filters are used in the adaptive noise shaping when the audio is a pure sine wave, and all that contributes to the non-linear, colorful and variable representation you may see on a graph.
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Old 04 March 2009, 09:50 am   #5
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thx

btw, who is that on Your avatar?
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Old 04 March 2009, 09:55 am   #6
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A girl I don't know, with a face I like .
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Old 04 March 2009, 05:09 pm   #7
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One more question; encoder in SV8 is 1.16 it`s "development" stopted from SV7 to SV8 becouse of lack of time or that the development of SV8 whose more important or the 1.16 encoder is just "rock solid" and there is nothing to change in the way it works ?.
What is the approach here: constant, never ending development and optimization to encoder or make it good once and enjoy it`s quality ?.
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