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AAC encoding from dff files
hlloyge
post Jan 31 2012, 10:51
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Hello all.

I have a question; I have a tune in dff (sacd rip) format which I obtained by shady sources, and it is not relevant for this discussion.

What I want to know is, how to encode it to aac? I am using foobar2000, and I loaded dff decoder plugin, and the song plays fine. But drum at the beginning peaks far above 0 dB, I guess it goes to +6. When I encode it to AAC, I use sox resampler plugin to convert it to 44100, but then it also peaks far above, but a bit less, I guess something about +3 or +4. I think it is because it is decoded AFAIK to 32bit float, which can handle higher peaks. I don't hear distortion whatsoever in original and encoded file, at least not on my desktop speakers, I haven't done any ABX test.

The question is - is this OK? I know mp3 doesn't have bit depth in the normal way wav file has; but I don't know about AAC. Can it handle that high input for encoding and decode it properly, without artifacts, or would I have to use some sort of peak limiting before encoding, or just decode it to wav and then load it up in Audacity and normalize it's peak limits to zero?

Thank you.
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benski
post Feb 2 2012, 01:28
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One thing I've always been curious about - and perhaps Chris could answer - does the PNS tool (Perceptual Noise Substitution) create any non-determinism in decoding? Or is the random number generator seeded from the bitstream somehow? I'm asking mainly from the point of view of peak value detection in ReplayGain (and compensation during playback) .

This post has been edited by benski: Feb 2 2012, 01:29
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saratoga
post Feb 2 2012, 01:47
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QUOTE (benski @ Feb 1 2012, 19:28) *
One thing I've always been curious about - and perhaps Chris could answer - does the PNS tool (Perceptual Noise Substitution) create any non-determinism in decoding? Or is the random number generator seeded from the bitstream somehow? I'm asking mainly from the point of view of peak value detection in ReplayGain (and compensation during playback) .


I don't know what the spec says, but libfaad's pns_decode uses a random number generator which is always initialized to the same value.

WMA Standard does something similar.
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benski
post Feb 2 2012, 02:27
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QUOTE (saratoga @ Feb 1 2012, 20:47) *
QUOTE (benski @ Feb 1 2012, 19:28) *
One thing I've always been curious about - and perhaps Chris could answer - does the PNS tool (Perceptual Noise Substitution) create any non-determinism in decoding? Or is the random number generator seeded from the bitstream somehow? I'm asking mainly from the point of view of peak value detection in ReplayGain (and compensation during playback) .


I don't know what the spec says, but libfaad's pns_decode uses a random number generator which is always initialized to the same value.

WMA Standard does something similar.


So playback from the start of the file would be OK, but "random" seeking could potential cause peak values to differ?
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saratoga
post Feb 2 2012, 02:34
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QUOTE (benski @ Feb 1 2012, 20:27) *
So playback from the start of the file would be OK, but "random" seeking could potential cause peak values to differ?


Ha, I suppose it would.

This post has been edited by saratoga: Feb 2 2012, 02:35
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