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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 29 2012, 19:04
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Anyways, anyone who ever heard a 6-bit PCM file knows this is funny. 6-bit PCM is incredibly noisy and it is the equivalent of the rough maximum resolution you can do with digital audio on the PC Speaker. Yes, I mean that little tiny beeper.

Here is a short part of a 192 kbps mp3 bitcrushed to 6-bits:
http://www.hydrogenaudio.org/forums/index....showtopic=98564
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saratoga
post Dec 29 2012, 22:21
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QUOTE (Neuron @ Dec 29 2012, 13:04) *
Anyways, anyone who ever heard a 6-bit PCM file knows this is funny. 6-bit PCM is incredibly noisy and it is the equivalent of the rough maximum resolution you can do with digital audio on the PC Speaker. Yes, I mean that little tiny beeper.

Here is a short part of a 192 kbps mp3 bitcrushed to 6-bits:
http://www.hydrogenaudio.org/forums/index....showtopic=98564


To be clear, MP3 does not work the same as PCM. 128kbit/s @ 44.1k is 2.9 bits per sample. Throw in ~ 2:1 lossless compression and you get very roughly 6 bits per sample. Actually when I tried this via the subtraction method (and using WMA rather then MP3) I got closer to 5 bits per sample. This puts a hard limit on the SNR because you only have a few bits, thus noise will be large as in your sample. However, lossy codecs are quite clever about distributing that quantization noise, and so you will find that 2.9 bits/sample on mp3 sounds quite a lot better then 6 bits/sample PCM.
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