Quality loss exporting .wav and reloading into audacity?

[noneleft]

I am recording old cassette tapes into Audacity, which I then process a little (with say normalise or amplify). Sometimes I want to save my project before finishing the processing. My question is why would I save as an audacity project (.aup) if .wav is a lossless format? Saving work in .aup project directories/files seem unecessary to the my uninitiated mind. In an attempt to understand can I ask the following:
1. Presumably I can save a new recording as .AUP and reload it into Audacity as many times as I want with no loss due to saving.
2. If I export a recording as .wav, then reload into audacity and re-export as .wav again, is there a loss? Can I do that infinitely with no loss?
3. What if I alternate between saving the project as .aup, then reloading it, and then exporting as .wav, then reloading it, then saving as .aup project etc. Is there any loss by switching between these two lossless save/export formats each time I want to save my work to be continued later?

Thanks, sorry for the simple questions, I just have a hunch that .wav is not quite lossless in some of these scenarios during processing phase before a final cut, otherwise why mess about with saving audacity .aup projects?

[kozikowski]

1. Presumably I can save a new recording as .AUP and reload it into Audacity as many times as I want with no loss due to saving.

You're not saving an AUP. You're saving a Project and the AUP file is merely the manager of the project. The show stuff is in the _DATA folder. Keep them together. Audacity Projects do not save UNDO.

Can I do that infinitely with no loss?

No. Audacity works internally at the insanely high quality 32-floating format. There is always some conversion damage, but it's reeeeely tiny. Going into Audacity is really lossless, but coming back out isn't.

3. What if I alternate..

Any time Audacity makes a 16-bit sound file, there is that tiny damage. You can eliminate all the damages by doing everything in 32-floating.

Koz

[steve]

There is always some conversion damage, but it's reeeeely tiny.

about 10000% smaller than the background hiss on a reasonably good cassette recording.

[kozikowski]

Oh, one more. Audacity Projects save your environment -- exactly what you were doing when you pressed Save (except UNDO). A sound file is just a sound file.

http://manual.audacityteam.org/o/man/au ... jects.html

We recommend exporting sound files periodically as you work to guard against the computer going into the mud and taking all your work with it. You can also Save Projects as different names as you go.

Also please note that Audacity has a mode where it doesn't make personal copies of external sound files. That can be dangerous and I think our default is to include them. It used to be default not to and people would "clean up" all those external music files and the Project would drop dead.

Koz

[noneleft]

Thanks for your swift answers. Do I conclude correctly then that saving work in progress as an audacity project is less lossy than saving work in a .wav file? If I repeatedly save work in a .wav file does it lose more each time I reload and export it (compared to if I had saved it using a project)? Or is it only the first time I export the .wav after recording? Perhaps I am asking if the audacity project saving keeps the 32 bit format when saved and reloaded? And if the .wav is constantly being converted between 16bit and 32 bit each time it is exported and reloaded into Audacity again?
Sorry if these are stupid questions.

[kozikowski]

Going from 16 to 32 is lossless. The quality of the target is very much higher than the source, but the return trip you're going "downhill" to a lesser quality format, so Audacity has to "guess" at some of the data values.

And again, we're talking vanishingly small errors in Music CD quality sound -- 44100, 16bit Stereo PCM.

Do all the production in 32-floating including the protection exports if it bothers you.

If your goal is a Music CD, then that's going to be 44100, 16-bit Stereo. There is no other option for Music CD. If you're headed for MP3, the compression quality is going to be the determining factor, not the WAV file that made it.

And all of these formats are pure gold compared to any sound you're likely to get from a cassette.

Koz

[noneleft]

OK thanks, I appreciate the general points you are making but I would really like to understand specifically what is the purpose and advantage (why / if it is actually superior) to save 'work in progress' using audacity projects rather exporting to and from wav files, in between edits.

Is it because the files saved in audacity projects are 32 bit whereas the wav files are 16 and therefore need to be converted between 16 - 32 each time they are exported and reloaded into the tool?

[Trebor]

... I would really like to understand specifically what is the purpose and advantage (why / if it is actually superior) to save 'work in progress' using audacity projects rather exporting to and from wav files, in between edits.

"dither noise" is usually added to WAV exports, ( unless it's 32 bit-depth, or you switch dither off ), so this noise can accumulate every time you open, modify then save the WAV file ... http://forum.audacityteam.org/viewtopic ... 178#p45178

[noneleft]

Thanks Trebor - those links have helped quite a bit. Without labouring the point I am concluding that audacity projects are not only processed in memory as 32 bits, but audacity projects are also saved to file in 32 bits, unlike wav, and this is where the dithering problem for wav comes in.

Sorry to all for being a pain, but this is mostly all new to me, and I like to understand things myself rather than just do what I'm told

[noneleft]

This leads me to (hopefully) my final question: Is there any reason NOT to use 32 bit wav as an export format for work in progress, other than file size?

If this can be successively loaded and exported with no accumulation of noise, or any other degradation, then it seems (at from a quality perspective) audacity projects do not add anything useful, but rather complicate matters (seeing as they proliferate their own directory structures and are not readable or as portable as wav files, and are more susceptible to corruption).

Thanks for all your answers.