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webby
11-06-2009, 21:15
Don't quite know how to put this...

If someone burnt a cd for me, how could I tell if they had burnt it from their mp3/aac rip or if they had copied it uncompressed? I mean, what happens when you burn an mp3 to disc as audio?

Beechwoods
12-06-2009, 06:37
You can rip a single track to WAV, load it into Audacity, select a few seconds and use the Analyse function to look at a graph of the Frequency Response. You'll see a very clear dip from about 15khz if it's MP3 sourced. Non-lossy will have good levels right up to 20khz+

You can also rip the disc to a single WAV file using xACT on the Mac and check for microgaps between the tracks; MP3 sourced CD Audio burns often have microgaps (often audible) between the tracks. Not conclusive but something to be aware of. Can also be caused by TAO burns.

And if you have access to a PC, Traders Little Helper has an analysis tool that can make a good probability recommendation about whether something is MPEG sourced, based on where the frequencies dip - a technical solution to method 1 above which relies on the user interpreting the Response Graph.

webby
26-01-2010, 14:49
So, this would be lossless yeah?

http://farm5.static.flickr.com/4017/4306777540_f8b6683cd5_o.jpg

Kris
26-01-2010, 15:01
Looks like an FM source to me (badly filtered pilot tone?). And yes, I'd say lossless.

The other problem is finding whether the original was 32kHz or 44.1kHz. Very difficult to tell at times.

webby
26-01-2010, 15:22
Well, it was maybe a flac download that I burned to cd, but I couldn't remember.

symon
26-01-2010, 15:49
Hmm, I'm not sure if that is lossless. MP3 tends to have a sharp drop at around the 15-16kHz frequency - I think. Nick will put me right if I'm wrong.
You also have to be a little careful, especially if the source is old. I think some cassettes had a similar drop off point which makes the graph look lossy, but isn't.

webby
26-01-2010, 16:05
It's a download of the 2nd disc of In Rainbows, so it's not old. I'm sure it was FLAC and I burnt it to cd, but I then put it into iTunes at 256 for some reason. I'm now re ripping so I wondered what it was.

Rare Bird
26-01-2010, 18:09
Don't quite know how to put this...

If someone burnt a cd for me, how could I tell if they had burnt it from their mp3/aac rip or if they had copied it uncompressed? I mean, what happens when you burn an mp3 to disc as audio?

If it's a live album or album where tracks continue into the proceeding track.MP-3 generally leave a micro pause between each track that should continue through as the original did.if you get my meaning.

Beechwoods
26-01-2010, 19:30
On the face of it that looks lossless, but it does look weird too.

The peak at the top end is strange; the 19khz peak looks very much like FM pilot as Kris points out. That is very odd given what you say the source was. It could be a high-bitrate MP3 or AAC which can look quite non-lossy these days. Check the track gaps in a one-wav rip, and try and get hold of a known non-lossy copy as a reference. I'd be interested to see what you find. I don't have a copy of In Ribbons to check myself.

Themis
26-01-2010, 19:53
Don't quite know how to put this...

If someone burnt a cd for me, how could I tell if they had burnt it from their mp3/aac rip or if they had copied it uncompressed? I mean, what happens when you burn an mp3 to disc as audio?


You can rip it with AccurateRip (EAC or dbPoweramp) and see if it corresponds to he Accuraterip database : if it does not, it's not lossless. ;)

Beechwoods
26-01-2010, 20:02
Nice one, Dimitri.

webby
26-01-2010, 21:55
Hmmm, I tried that with XLD and for track 1 I got this:

Track 01
Filename : 01 MK 1.m4a

CRC32 hash : 013CB88B
CRC32 hash (skip zero) : 1245E5FE
AccurateRip signature : 481371CD
->Rip may not be accurate.
Statistics
Read error : 0
Skipped (treated as error) : 0
Edge jitter error (maybe fixed) : 0
Atom jitter error (maybe fixed) : 0
Drift error (maybe fixed) : 0
Dropped bytes error (maybe fixed) : 0
Duplicated bytes error (maybe fixed) : 0

Some inconsistencies found

End of status report

But for track 2 I got this:

Track 02
Filename : 02 Down Is The New Up.m4a

CRC32 hash : 02D624EF
CRC32 hash (skip zero) : 03CE1D2E
AccurateRip signature : 6DC4CB90
->Accurately ripped! (confidence 9)
(matched with the different offset correction value;
calculated using an additional offset of 175;
the signature after correction is: 55061BE9)
Statistics
Read error : 0
Skipped (treated as error) : 0
Edge jitter error (maybe fixed) : 0
Atom jitter error (maybe fixed) : 0
Drift error (maybe fixed) : 0
Dropped bytes error (maybe fixed) : 0
Duplicated bytes error (maybe fixed) : 0

No errors occurred

End of status report