Why re-compress unchanged audio tracks

[DickN]

I often save a compressed project to work on later, eventually doing Export Multiple to MP3. Typically all I do in these projects is filtering or noise removal and then add or edit a label track. When I re-save it as a compressed project, it updates all the audio tracks. They 'always' get smaller, so I must be losing something each time. If I just Save it (Ctrl-S), my .aup file references an uncompressed e0 directory, which appears in the folder. Also, before I started using compressed projects, I copied pieces of audio liberally into new tracks and exported by track name rather than label knowing that Audacity wouldn't actually copy the data to use it in a new track. Now I keep it all in one track.

What I'm requesting is this: If the audio in a track has not been altered, then don't update the .ogg file. My workaround for this has been to save the compressed project somewhere else, copy the .aup file back from there and delete the newly saved project. This wastes a lot of time generating .ogg files that will be discarded.

One more request: A warning when saving a project that was loaded from a compressed project.

[billw58]

Why are you saving compressed projects? Are you short on disk space? Every time you compress (using OGG, MP3 or any other lossy format) you lose quality. Forget compressed projects and just save the Audacity project. Just remember to keep the .aup file and the _data folder together. Some people find it convenient to put them together in their own folder.

-- Bill

[DickN]

I use compressed to squeeze several church services onto a thumb drive 'cause my laptop is getting full. Since I'm exporting MP3's anyway for this I don't think the loss in the ogg will amount to much. Also there are parts I don't export for the podcast and I want to keep the projects around for a few weeks in case I'm asked for something I might have recorded but didn't put in the podcast.

Just opening the project replaces the .aup file with one that references the uncompressed e0 folder it just made.
Before I found out about compressed projects I was exporting a flac and label file. I could recreate the project from just those. Save Compressed Project seemed simpler.

[waxcylinder]

You can get quite big thumb drives these days.

And you can get (relatively cheaply) portable 0.5TB & 1TB pocket USB disks - of a size that easily fits in a jacket pocket. Here's an example found at random on Amazon: http://www.amazon.co.uk/including-Softw ... 68&sr=1-10

My son has one (not the one referenced above) for his work use and finds it very rugged and reliable in use.

With bigger storage you can export the recorded project to an uncompressed WAV file on the portable drive.

WC

[bgravato]

With bigger storage you can export the recorded project to an uncompressed WAV file on the portable drive.

DickN mentioned he was already exporting as FLAC+labels file before founding about compressed projects, so I guess that's not the issue here.

Regarding external hard-drives I'm pretty happy with my iomega 2.5" 320GB (they make it in 500GB now too). It's quite small and light. Nonetheless it's still considerably bigger than a flash drive and harddisks always require more careful handling than flash.

[waxcylinder]

Yes, but the poster did go on to say that he was using <<compressed to squeeze several church services onto a thumb drive 'cause my laptop is getting full>>. Hence the bigger external drive suggestion

And yes, I like Iomega drives too. I have one of their 1TB desktop USB disks (my wife has two, bouught after seeing mine), but it is certainly small enoungh to be portable in a briefcase, or a laptop bag 20cm x 12cm x 3cm. I carry it to my son's house occasionally to make an offsite backup of all my production/archive WAV files.

WC

[DickN]

Actually the thumb I use for this currently has a couple of uncompressed projects taking up most of it. I only compress the less critical ones (i.e. those that will wind up as MP3's). I apply effects (noise removal, filtering, volume compression etc.) before making a compressed copy. Thanks for the USB HD suggestion though, will look into it.

My original post was not about why one would ever use the feature, but about already-compressed sound files that didn't need updating getting rewritten by compressing Audacity's working files which were derived from them, as I often edit the label track before exporting and may do this in multiple sessions.

Also, as I discovered recently, I lose the "compressed project" version of the .aup file just by opening the project. The workarounds for these issues are simple but one has to know about the behavior and remember to use the workaround. If one does not use the workaround, which is to make a copy of whatever files one is not going to alter and copy them back later, then the degradation due to lossy compression is compounded unnecessarily. Moreover, the needless rewriting of "unchanged" files takes a long time due to the compression algorithm.

[bgravato]

I haven't used the compressed project feature yet, but if it behaves like DickN said, then I must generally agree with what he says. If this goes to the wiki add a +1 vote for me please.

[steve]

My original post was not about why one would ever use the feature, but about already-compressed sound files that didn't need updating getting rewritten by compressing Audacity's working files which were derived from them,

That suggests that Audacity is accessing compressed audio files within the project, but that is not the case. Audacity always works with uncompressed audio and can only work with uncompressed audio. This means that when you open a "Compressed Copy" of a project, all of the audio data is immediately uncompressed. When you save the project again, it is the current audio data (the uncompressed audio data) in the project that is saved.

Before I found out about compressed projects I was exporting a flac and label file. I could recreate the project from just those. Save Compressed Project seemed simpler.

So how about if there was an option to select FLAC as the compression format for compressed projects rather than Ogg?

[DickN]

When you save the project again, it is the current audio data (the uncompressed audio data) in the project that is saved.

I understand that when saving a Compressed Project, Audacity is compressing its current audio data regardless of its original source, but what I'm saying is that if a track's audio data has not been altered and the original source for this session was a Compressed Audacity Project, it should not update the .ogg file for that track.

So how about if there was an option to select FLAC as the compression format for compressed projects rather than Ogg?

I'm in favor of having that option, and I would use it quite a lot. My previous statement would still apply, however, if only because of the time involved in generating the compressed data.

My other issue was losing the "compressed project" version of the .aup file when opening a compressed project.