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SNR of MP3, Split from Topic ID #96702
benski
post Aug 28 2012, 18:37
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QUOTE (jensend @ Aug 27 2012, 11:45) *
The LP noise floor is rather high- maybe -70dB under very good conditions. 12-bit sampling (RMS noise floor of -72dB) would be sufficient for LP use as long as your levels are right (peak signal above -6dB). (12-bit sampling was used for DV but hasn't seen any other widespread use).


The SNR of an MP3 is around 25-30dB. Does this mean that I only need to decode them to 6-bit PCM to capture all the details?

I am curious if anyone has ever done a detailed analysis of an LP's SNR in different frequency bands.

This post has been edited by benski: Aug 28 2012, 19:07
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pdq
post Aug 28 2012, 20:20
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QUOTE (benski @ Aug 28 2012, 13:37) *
The SNR of an MP3 is around 25-30dB.

I don't know why you say that. The dynamic range of mp3 is obviously much greater than 30 dB.

I would be more inclined to describe mp3's deviation from the original as distortion rather than noise, because it is quite capable of rendering very quiet passages with very little added noise.
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Neuron
post Dec 31 2012, 00:39
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What does "noise" mean in the case of mp3s anyways? How would that noise sound if it wasn't masked? What does a 2.9 bit depth even mean for mp3? How does a codec with ~30 dB signal to noise ratio have a dynamic range of ~150 dB? Honest questions, lossy compression is really starting to confuse me huh.gif .

And what is the effective SNR of mp3? As in, does an average mp3 sound like a linear PCM file with a SNR of 96? 90? 80? 75? 70?

If mp3 has a signal to noise ratio of only 15-30 dB, how come it is close to the original sound not only when listening but also when looking at it in an audio editor? How come the waveforms are similiar to the original and don't look or sound noisy at all? If it was all psychoacoustic tricks and the waveform was in reality a noisy, 2.9 bit mess, it would show up in an audio editor. Yet there are no obvious faults except for a lowpass for the highest frequencies.

This post has been edited by Neuron: Dec 31 2012, 00:49
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saratoga
post Dec 31 2012, 00:49
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QUOTE (Neuron @ Dec 30 2012, 18:39) *
What does "noise" mean in the case of mp3s anyways?


See Woodinville's post above.

QUOTE (Neuron @ Dec 30 2012, 18:39) *
How would that noise sound if it wasn't masked?


Masking is the process of making something in audible. Masked noise is therefore inaudible.

QUOTE (Neuron @ Dec 30 2012, 18:39) *
What does a 2.9 bit depth even mean for mp3?


(128000 bits/second) / (44100 samples/second) = 2.9 bits per sample. Thats all it means.

QUOTE (Neuron @ Dec 30 2012, 18:39) *
How does a codec with ~30 dB signal to noise ratio have a dynamic range of ~150 dB? Honest questions, lossy compression is really starting to confuse me huh.gif .


Dynamic range has nothing to do with SNR. The former is just the ratio of the largest magnitude to the smallest, while SNR is the ratio of the maximum signal value to the noise power.
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Neuron
post Dec 31 2012, 01:04
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QUOTE (saratoga @ Dec 31 2012, 00:49) *
QUOTE (Neuron @ Dec 30 2012, 18:39) *
What does "noise" mean in the case of mp3s anyways?


See Woodinville's post above.

QUOTE (Neuron @ Dec 30 2012, 18:39) *
How would that noise sound if it wasn't masked?


Masking is the process of making something in audible. Masked noise is therefore inaudible.

QUOTE (Neuron @ Dec 30 2012, 18:39) *
What does a 2.9 bit depth even mean for mp3?


(128000 bits/second) / (44100 samples/second) = 2.9 bits per sample. Thats all it means.

QUOTE (Neuron @ Dec 30 2012, 18:39) *
How does a codec with ~30 dB signal to noise ratio have a dynamic range of ~150 dB? Honest questions, lossy compression is really starting to confuse me huh.gif .


Dynamic range has nothing to do with SNR. The former is just the ratio of the largest magnitude to the smallest, while SNR is the ratio of the maximum signal value to the noise power.


So the 2.9 bit/sample figure for mp3 does not represent resolution, just mathematics? And how would mp3 noise sound if it was unmasked?

This post has been edited by Neuron: Dec 31 2012, 01:05
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