How to reduce size of a FLAC file without damaging its quality?

Question

I got collection of vinyls which I paid for them to be digitized in FLAC. However my Hard Drive is getting full (91% full as of today) and the smallest of these vinyls is 2.3 GB in size!

I would like to reduce the size of these files as much as possible, but don't know much about this. What I've read is that FLAC supports different levels of compression. But since it is a lossless format, all of them contain the same information. Obviously a higher level of compression would require more time to play, but that wouldn't be a problem for me since what I want mainly is to preserve them.

So I think my questions would be:

1. How do I determine what level of compression the files have?
2. Assuming they are not fully compressed, how can I change their compression?

Answer 1

You can encode flac to flac. Not sure how much the compression level will help, though. I tested with a voice message recorded by my IP phone.

for level in {0..8}
do
    flac --verify -$level -o tam818.$level.flac tam818.flac
done

Result:

$ stat -c '%s %n' *.flac | sort
232049 tam818.8.flac
232406 tam818.7.flac
232845 tam818.6.flac
233596 tam818.5.flac
233596 tam818.flac   # so original was level 5
234490 tam818.4.flac
234991 tam818.3.flac
241091 tam818.0.flac
241091 tam818.1.flac
241091 tam818.2.flac

So it saved ~1.5K for a ~230K file. Let us know how much it helps for your vinyls... flac also has even more options, for example adding -p frees another 300 bytes for me. Not really worth the effort though, if you expect a 50% reduction you're probably out of luck.

the smallest of these vinyls is 2.3 GB in size!

Static data less than 4.7GB in size sounds like an ideal application for DVD-R media. Make at least two copies + checksum/parity, lock them in a dark place, refresh every X years (although most like you'll have a large enough HDD until then), and keep a high quality OGG/MP3/??? for day-to-day use.