Old 29th March 2009, 03:01   #1
DamageIncM
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FLAC Compression Factor?

So, I've been wondering the following for a while now:

You know how you can set a slide from '0' to '8' under 'CD ripping preferences...',
'Encoder'-tab and then using the FLAC-encoder.
When the slide is farthest to the left it's described as 'Fast Encoding' and to the right would be 'Best Compression'.

Now, I assume the first would mean faster ripping
and the latter would mean smaller files but longer encoding (if that actually refers to the ripping-process).

If so, is that all it does, or is there a (slight) quality-difference?
Which is actually my main concern.

If not, would the descriptions refer to the quality of the ripped audio?


I've checked both the file-sizes in the files their properties and the qualities (kbps-number in Winamp's display),
setting the slide to each farthest end, ripping the same track from the same (original) CD.
But it turns out the files are exactly the same, as far I can determine without additional software.
So what does this actually do at all?...

- Damage Inc.
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Old 29th March 2009, 03:45   #2
millercommamatt
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Without getting too technical, I'll say that the setting for FLAC encoding sets the amount the file gets compressed. The change in compression ratio between the highest and lowest settings is a rather small difference. Regardless, of what setting you choose, the playback quality should be identical. The setting you choose just determines small differences in the compression ratio of the file and the trade off is that slightly more compressed files require more time to encode.

If you're looking for a more technical explination of what exactly the setting does, read up on the FLAC standard and specifically Golomb-Rice coding.
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Old 29th March 2009, 06:58   #3
DamageIncM
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OK, that pretty much explains it.

And what is the Golomb-Rice coding exactly?
It's what... I guess, FLAC is built on? Like it's platform...

Thanks for your reply.

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Old 29th March 2009, 07:16   #4
millercommamatt
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Golomb-Rice coding is a lossless data compression method. Here's a wikipedia link that explains the technical details:
http://en.wikipedia.org/wiki/Golomb_coding
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Old 29th March 2009, 16:24   #5
DamageIncM
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Quote:
Originally posted by millercommamatt
Golomb-Rice coding is a lossless data compression method. Here's a wikipedia link that explains the technical details:
http://en.wikipedia.org/wiki/Golomb_coding
So, it's a different one from FLAC?
Or is the method used Ã_n FLAC?

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Old 29th March 2009, 22:14   #6
millercommamatt
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FLAC uses that type of encoding.

Wikipedia provides a simplistic explanation of the whole FLAC encoding process.
http://en.wikipedia.org/wiki/Free_Lossless_Audio_Codec
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Old 30th March 2009, 09:21   #7
DamageIncM
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Thanks! I'll look into it.

Another thing about FLAC-files though:

Of course the bitrates are quite high, which represents the quality right?
But what I noticed is that some rips are over a thousand kb/s and some are hundreds below a thousand.
That can be from different CDs but also different tracks from the same disc.

Now, I also noticed that usually the shorter tracks have the lower values.
For example, out of my rips, the track with the lowest value of 553kb/s is 0:13, because it's an intro to an album.
But the next lowest one, with 560kb/s, is a song of 2:10.
Then the one with the highest value, of 1227kb/s, is 4:44.
Only the longest track is 13:54, which is 1012kb/s.

Is this because there are just less kb's in the file or... how does that happen?
Does the lower amount of kb/s also mean the quality is lower or is it,
as said, just an indication of how many kb's there are in the file.
Then again, it does say how many per second...

Or, does this actually really show what quality the audio on the disc is?
As it's lossless, so it might take the same quality directly off the disc.


A little confusing. :P

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Old 30th March 2009, 09:31   #8
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FLAC is lossless, basically means you are getting CD quality. (Lossless meaning no loss, as compared to lossy compression such as MP3 or WMA which information and quality is lost). Compression factors can be based on a lot of things, so I wouldn't say it is a measurement of original quality. (A track with a lot of silence or repetitive sounds may compress a lot more then a track that is totally unique all the way though).

Pure CD Audio is 1411.2kbps. FLAC will be varying degrees below that. But with FLAC (or any lossless encoder, in theory, you can compress the file and the uncompress it and it will be a perfect match to the original CD).

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Old 30th March 2009, 09:58   #9
DamageIncM
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Quote:
Originally posted by Sawg
FLAC is lossless, basically means you are getting CD quality. (Lossless meaning no loss, as compared to lossy compression such as MP3 or WMA which information and quality is lost). Compression factors can be based on a lot of things, so I wouldn't say it is a measurement of original quality. (A track with a lot of silence or repetitive sounds may compress a lot more then a track that is totally unique all the way though).

Pure CD Audio is 1411.2kbps. FLAC will be varying degrees below that. But with FLAC (or any lossless encoder, in theory, you can compress the file and the uncompress it and it will be a perfect match to the original CD).
Hm, well I understand it's lossless and what it means.

So, FLAC actually compresses it in size, only despite that it would let through a lower bitrate, it's just not audible?
Which I guess is the purpose of it.

But you're saying that I could uncompress it to get a perfect match.
You mean with software like 'ExactAudioCopy' or something like that?
(Unless that specific one is only meant to rip with, but you know.)
But would it uncompress to FLAC once again or would it have to become another file (I would guess WAV)?

Still, how does it determine which bitrate to go at?
Or rather, why are all these bitrates so inconsistent?
I mean, of course, throughout different tracks, because throughout one track it IS consistent.

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Old 30th March 2009, 10:26   #10
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The decoded flac file is identical to the wave file you encoded it from. The encoder doesn't determine any "bitrate to go at". It just encodes the audio with the settings you told it to use. Most programs only report the average bitrate which is (almost) as simple as filesize / length. This is because flac is VBR, different parts of a file can be encoded into any amount of bits.

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Old 30th March 2009, 10:31   #11
DamageIncM
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Quote:
Originally posted by J_Darnley
The decoded flac file is identical to the wave file you encoded it from. The encoder doesn't determine any "bitrate to go at". It just encodes the audio with the settings you told it to use. Most programs only report the average bitrate which is (almost) as simple as filesize / length. This is because flac is VBR, different parts of a file can be encoded into any amount of bits.
It's variable? I thought it was fixed.
Anyway, I didn't think so because the "counter" in Winamp always stays the same when playing FLACs.
Not to say it's some highly advanced deal,
but just that it would usually jump around with downloaded MP3s that have variable bitrates.
Maybe it just can't do that with FLAC-files, I don't know.

So there is also no need to uncompress it to like get the full files?

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