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I ripped a CD to FLAC. Comparing the two versions of the same song with MediaMonkey, I noticed the original CD bit rate is 1411 kbps:

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whereas the FLAC file has a bit rate of 906 kbps:

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Why is this? Is this a loss of data, or just a reflection of the compression (i.e. decompression while playing reverts the bit rate back to the CD's original bit rate)?

11

It's just how bit rate is defined. It's "bits of data per second". So if you compress something, even losslessly, it's at a lower bitrate.

The association between "low bitrate" and "low quality" comes from lossy codecs like MP3, which let you trade off quality for file size. Lossless codecs like FLAC instead let you trade off CPU time (at least during compression) for file size.

4

Since FLAC by definition is lossless compression there shouldn't be any data loss unless there is an error during encoding.

In my experience, when you compress a WAV file to FLAC it reduces the size by about 1/3. (The FLAC web site claims even better compression, and as @Mulvya pointed out in the comments, this is due to the content of the recording). The bitrate for the FLAC file you have is about 1/3 less than the bitrate of the WAV file.

I would guess that the numbers you are seeing are probably due to the compression.

  • The amount of compression depends on the source material. I typically get 80% compression with voice-only tracks. 55% for typical orchestral music, 65% for solo instrumental music, and so on. – Mulvya Mar 27 '12 at 14:29
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    That explains it. The comparisons I made were of recordings of a full band. I guess the cymbals and screaming guitars don't compress so well. :) – Friend Of George Mar 27 '12 at 14:59
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FLAC is Free Lossless Audio Codec where Codec = co mpressor/dec ompressor, so yes the lower bitrate is due to compression.

And yes, the original stream is obtained upon decompression.

  • actually, "codec" is a portmanteau of "coder-decoder", according to Wikipedia (en.wikipedia.org/wiki/Codec) – Ben Sandeen Sep 5 '18 at 19:20
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    Likely, as more sources state this. But I must have originally seen a different source, the same as Adobe. – Gyan Sep 5 '18 at 19:53
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FLAC is a lossless audio encoder so the bitrate is nothing other than an indication of the compression ratio FLAC has been able to achieve. Since FLAC is not allowed to change the material at all, the better the material matches its predictions (and the more time FLAC may spend on compression), the higher the compression ratio will be.

That means that microphones and preamps and recording equipment with excellent SNR ratio (so sorry, my dear tube amps) will pay off also with better compression ratio since noise is pretty much the least predictable material (and thus compresses rather badly), so the less you have of it in your signal, the better the compression has a chance to be.

Lossy compression can decide to toss a certain amount of noise or replace it with something similar. FLAC does not have that luxury.

1

CDs came from a time when portable processing capability was relatively limited. Raw PCM data, such as what is on a normal CD or a normal PCM wav file is a direct representation of the audio waveform. It is extremely easy to reproduce the audio from, but doesn't make any attempt to limit it's size.

FLAC is a newer format which makes use of lossless compression to store the same exact data (lossless) but in a compressed manner so that it takes less space. A variety of techniques can be used to achieve lossless compression, but they effectively involve finding patterns in the data and then storing the pattern rather than every incidence of the pattern. This allows for potentially much smaller amounts of data to be used to represent the same stream, but it means that the decoder has to put the jigsaw puzzle back together before it can actually meaningfully play the file. This means that a player needs a lot more processing capability to play the audio back, but can use less space to store it.

Additionally, it has the disadvantage of not being a linear read. CDs were basically the digital equivalent of a record player. They could read the data linearly and play it back (hence Linear PCM) where as FLAC requires reading the entire file at once which wouldn't have worked for CDs in the early days even without the processing issues.

As for an example of how lossless compression can work in a general case, lets assume you had the following string

The elephant can see that the dog can see that the elephant is here.

We can notice that The, cat, see, can are all used multiple times, so we say:

1=the 2=elephant 3=see 4=can 5=that 124351dog43512is here.

As you can see, all the same information is there, but it took less space. The exact ways that patterns are recognized vary based on the format and type of data, but the result is still the same, the information density is increased resulting in the same amount of information stored in less space.

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The WAV file on the CD is normally uncompressed.

The FLAC file is compressed, with "lossless" compression, which means that decompressed it will yield the exact same contents as what was fed into the compression process.

Since the FLAC file is compressed it will normally be smaller than the WAV file.

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CD files also contain metadata in each music file, date, title, recording info and ripping leaves that behind.

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    This answer is simply flat out wrong. A) not all (many, possibly most) CDs don't have meta data. B) FLAC files DO contain meta data. – AJ Henderson Dec 8 '17 at 17:20
  • This is false in fact there is no support in the IEC 60908 standard for metadata beyond the 8 byte TOC entry for each track which just gives a 1 byte track number and the location of ther audio data start on the CD. – MttJocy Feb 22 '18 at 7:01
  • In fact many audio players on devices that have an internet connection will just go direct to querying the online metadata DB and pull track names from there rather than taking the time to scan for a second session on the disk containing a CD-Text file inside an ISO 9660 filesystem. That said probably 90% of computers can pull a <1 kB gzip compressed text response from a local internet mirror faster than an optical drive can finish re-positioning the laser to even begin looking to see if said file exists or not. – MttJocy Feb 22 '18 at 7:44