Compression Level Audio Quality

[Pyrosma]

Hi,

This morning I ran a FLAC batch conversion of Level 5, 7, and 8 compression and saw zero difference in the size of each. My original original FLAC files are all uncompressed, so that library is 50% larger in size.

My question is whether there are any real differences between the audio quality of each compression level to the human ear?

Thanks in advance.

[Dat Ei]

Re: Compression Level Audio Quality

Flac uses data compression, not audio compression.


Dat Ei

[garym]

Re: Compression Level Audio Quality

No difference in audio quality (and not just perceived; literally NO difference). All FLAC files are lossless. Regardless of which compression level used, all FLAC files are decoded back to the original pcm data of the CD upon playback. More data compression simply means the computer works a bit harder when encoding the files (a one time thing). But generally the *decoding* of the files is virtually the same processing independent of FLAC file compression level.

SHORT ANSWER: No, and using uncompressed FLAC is simply a waste of hard drive space. But at least it is better than WAV files, because it allows better tagging capabilities.

[schmidj]

Re: Compression Level Audio Quality

The compression part of FLAC is the equivalent of zipping a data file (although the actual methodology is very different). What goes in is what comes out. Bit by bit the same. Lossless audio codecs just use more storage space efficient methods of encoding the data before writing it to the storage media. The different levels of compression are simply less or more space efficient methods of encoding the same data, the decoded output is bit identical.

The more space efficient (higher number) levels of compression are more computationally intensive, and therefore take longer to process when being encoded. (the decoding time varies little with compression level.) So the tradeoff is storage space versus processing time for an identical playback result.

The WIKI on FLAC deserves a read. There is a table there from a study of encoding efficiency (file space saved), encoding time, and decoding time for a sample audio file. The results were that the higher levels saved almost no more space (at least for the sample file that was used in the study) but took much more processing time to encode. All of this is pretty much academic these days with fast processors and cheap storage. I have always used the default level 5.

The only folks that might seem to have good reason to use the higher levels would be those storing the files on small removable media (USB sticks, HD cards) But first, most people will use a lossy codec with those storage devices, as the generally slight loss in quality due to "reasonable" (the end user has to determine what "reasonable" is, what is reasonable in my car might not be in my home theater) amounts of lossy compression is typically a fair trade-off for being able to store a lot more content on the same size storage media. But second, it appears that, again with the example file used in the study, using higher levels of FLAC compression was an exercise in futility, the processing time went way up, but the resulting file was almost the same size.

So take your pick, with FLAC the bits come out the same, therefore the audio playback is identical to the source.

But even FLAC 0 saves close to 30 percent of your storage space compared to the PCM (read .wav) source audio data, and as Gary says, tagging in FLAC is much more standardized, and therefore supported, than .wav files. The metadata support should be reason enough to use FLAC irregardless of the storage space savings.

[Pyrosma]

Re: Compression Level Audio Quality

Thanks, you guys rock.

I've had the Pioneer XDP-100R hi-res audio player for some time, which has two Micro SD slots, so it can easily fit my collection. However, I recently picked up a FIIO M7 my wife and it only has a single slot, which is why I was testing the size of data.

Schmidj, I'll go take a look at that FLAC table, too.

Thanks, again, all.

[Michael Sargent]

Re: Compression Level Audio Quality

I'm not sure what article schmidj was referring to (no link), but I found this:

http://z-issue.com/wp/flac-compression-level-comparison/

It shows that higher levels do keep compressing better and since compression is done in the background, who cares how long it takes? I encode everything at level 8 and have never had a problem. And with 2.81 TB of digital music, I can use all the disk space saving possible.

Mike

[Pyrosma]

Re: Compression Level Audio Quality

Here's the link to the FLAC Wiki:



My goal was to decide what size Micro SD to purchase, because they have a much higher storage cost than hard drives. My library is less than a 400 GB, but now that me and my wife both have players now I just needed to understand if compression compromised audio quality.

Agreed, re: higher compression rates vs. encoding time.

Appreciate all the info.

[schmidj]

Re: Compression Level Audio Quality

Look at https://en.wikipedia.org/wiki/FLAC. Look at 3.3, compression. I cannot vouch for the study, only that I saw and read the table. Your link has a similar table that shows that going from FLAC4 to FLAC8 gained about 3/10ths of one percent in additional compression. Now, if space is of the essence, sure, why not use FLAC 8. Just be aware that the resulting file has only gotten ever so slightly smaller. But nothing lost but a little processor time in encoding, not an issue these days, and it will play back bit perfect like FLAC 0 or .wav.