Typical signal to noise ratio of ADPCM Options

[Neuron]

So, I have decided to return to this forum (despite my little conflict with greynol) and I have kind of a weird question. I would like to know what is the rough SNR of a 4-bit ADPCM recording (IMA and Microsoft). For those curious why I am asking this, well, I like ripping music and sound effects from old games, and I would like know the technical side as well.

[Neuron]

Thank you, but what does "signal: -19 db", ratio of signal to what? If the next values compute the RMS of noise.
Can you try doing it with regular 8-bit PCM vs. 16-bit original? The results seem counter-intuitive, MS ADPCM sounds better than IMA (and I provided an ABX test to prove that I indeed hear a difference and that it is the IMA file which sounds noisier to me). The SNR you got corresponds to a 5-7 bit signal which sounds much worse than either of the ADPCM or an 8-bit version.

I understand that in for example mp3, dynamic range and SNR don't really relate and mp3 has a dynamic range of about 144 dB while frequently having a SNR of 20 dB or even lower. However, mp3 masks the noise by clever psychoacoustic methods. ADPCM does not do any psychoacoustic tricks so if the SNR is about 38 dB it should sound as bad as 6-bit PCM but it doesn't. When I'm thinking about it, what is the dynamic range of ADPCM anyways? Will it be 96 dB because of being decoded to 16-bit PCM, but with a low SNR, thus explaining the paradox?

[extrabigmehdi]

Thank you, but what does "signal: -19 db", ratio of signal to what? If the next values compute the RMS of noise.

It's the value returned by the normalize function of soundforge.
If you have -19 db for signal, and -38.2 db for noize, then you can deduce,
that the signal is 19.2 db louder than the noize (38.2-19).
I guess 0 db, would represent the loudest signal that the normalize function could measure on a file.

Regarding 8 bit , well I decreased the bit depth of your file "Eric_Brosius___02___Med_Sci_1___44_Khz_lossless.flac"
to 8 bit using the most straightforward algorithm (no noise shaping).
Then again using most straightforward algorithm, I've converted it to 16 bit,
and calculated difference with original file.
RMS of difference measured , is -96 db, which could be interpreted that there's no meaningful (or no) difference.

EDIT: I've done the same experience, with a random file, similar result, not sure what to conclude.

EDIT 2: Listened to 8bit version of my random file from speakers, it doesn't sound bad to me. I won't do an ABX test though.


This post has been edited by extrabigmehdi: Jan 30 2013, 16:06

[Neuron]

Thank you, but what does "signal: -19 db", ratio of signal to what? If the next values compute the RMS of noise.

It's the value returned by the normalize function of soundforge.
If you have -19 db for signal, and -38.2 db for noize, then you can deduce,
that the signal is 19.2 db louder than the noize (38.2-19).
I guess 0 db, would represent the loudest signal that the normalize function could measure on a file.

Regarding 8 bit , well I decreased the bit depth of your file "Eric_Brosius___02___Med_Sci_1___44_Khz_lossless.flac"
to 8 bit using the most straightforward algorithm (no noise shaping).
Then again using most straightforward algorithm, I've converted it to 16 bit,
and calculated difference with original file.
RMS of difference measured , is -96 db, which could be interpreted that there's no meaningful (or no) difference.

EDIT: I've done the same experience, with a random file, similar result, not sure what to conclude.

It is not an 8-bit file converted to 16-bit. I've done the same thing as you did and I got a normal noise signal at -48.2 dB as expected with an undithered 8-bit file (and the result was usual 8 bit noisy music), as I said in the post before. The other results of my experiments are very weird through...