If I have a MP3 file compressed at a certain bitrate (without having the original source media or a lossless other source file) and I convert it to FLAC or any other lossless format will the resulting file be equal to a lossless file of the original source?
My thinking is the following: If I compress a data file using ZIP I will always will be able to get back to the original data file content when unzipping, i.e. no data is actually removed.
Does MP3 compression actually remove something or does it just and only compress the data?
If I have a MP3 file compressed at a certain bitrate (without having the original source media or a lossless other source file) and I convert it to FLAC or any other lossless format will the resulting file be equal to a lossless file of the original source?
My thinking is the following: If I compress a data file using ZIP I will always will be able to get back to the original data file content when unzipping, i.e. no data is actually removed.
Does MP3 compression actually remove something or does it just and only compress the data?
Hi,
Codecs fall into two categories, lossy and lossless.
Once source material has been encoded using a lossy codec there is no way to get back the lost information (other than re-encoding from the original source material using a lossless codec).
Source material that has been encoded using a lossless codec can then be converted to another lossless format with no loss in quality. Lossless codecs can also compress the data as part of the encoding process, but that is not necessarily a property of a lossless codec.
Zip is an example of a lossless codec (that also compresses the data). Zip therefore would fall in the same category as Flac.
David
Thank you very much !!
Just in case this wasn't obvious - MP3 is a lossy codec, and so you will not regain the lost information by transcoding to FLAC. The lower the MP3 bitrate, the more data that's been lost.
'Source material that has been encoded using a lossless codec can then be converted to another lossless format with no loss in quality.'
I beg to differ on this common wisdom that conversion from one format to another, whether lossless or not, gives the same results. My ears just don't bear this out after repeated lossless conversions.
There are others in the forums here who would agree that the different lossless formats don't exactly sound the same. By the same token is it so far-fetched that conversions between them would also not sound the same?
I find it's still best to rip from the original source.
manicm,
It is feasible that media in different file formats might sound marginally different. Each format requires a different amount of processor effort to decode and a different amount of network activity to fetch. It is not impossible that the marginally altered balance between these fetching and decoding activities might alter the electromagnetic environment in such a way that might be discernible.
In my opinion this difference would be at a similar level to the difference in listening experience that occurs when ones heart-rate goes up or down by one beat per minute or the air pressure adjusts by a few millibars, or a different set of large vehicles are situated on the road outside your house, etc
However, it is nonetheless possible that a systematic difference might be detectable by some.
Lets us call this SONIC FORMAT DIFFERENCE.
Now what you propose is that there might be a sonic difference between, for instance, the following:
a) Rip to WAV -> Convert to ALAC -> Convert to FLAC -> Convert to WAV -> Convert to FLAC
b) Rip to FLAC
Let us call this the SONIC GENERATION DIFFERENCE.
You seem to be asserting two things:
a) The existence of SONIC FORMAT DIFFERENCE implies the possibility of SONIC GENERATION DIFFERENCE
b) SONIC GENERATION DIFFERENCE exists.
I would claim that both these assertions are wrong.
Graham
You said that in a more restrained way than I feel I would have, Graham.
:-)
You haven't proved those assertions are wrong, in fact you're contradicting yourself by admitting different lossless rips can give different results.
The truth is unless someone knows the innards of audio compression we'll never really get the full picture.
I maintain to obtain the best results always rip from the original source if possible and never from copies.
I can give you one example:
I purchased the CD-quality WMA rip of Palladian's Devil's Trill from Linn, and subsequently ripped to MP3 at 320k. I was then allowed a download of the MP3 files from Linn (after a lost CD order). And I can tell you the two MP3 sets did not sound the same. The direct MP3 download sounded better and smoother.
manicm,
Quite a few people know the truth about the innards of audio compression. I am one of those people and I am trying to avail you of that knowledge.
Graham
manicm,
A lossless audio file, such as an ALAC or FLAC file, is a compressed, yet faithful representation of an audio waveform. They use different techniques to achieve this faithful compression, so the resulting compressed files are different. But if you decompress an ALAC and a FLAC file of a particular track you will get exactly identical waveforms in both cases.
This means that you can compress and decompress in and out of any lossless format as many times as you wish without making the tiniest change to the waveform that is represented.
This is what is meant by the term 'lossless'.
Naturally, this does not apply to MP3, which is a lossy compression system.
Graham