Need some information regarding "lossless" editing

Hi. So the situation is that I have a lot of ripped CDs and vinyl records in various formats: most of them are 44.1 khZ / 24-bit, but there are also a lot of files in 16-bit, either FLAC or WAV. I want to edit these audio files in a lossless way - cut out and move around only the parts of the songs that I like, then export them as WAV. I would also like to clean some songs (mainly the vinyl ones).

Here are the questions:

  1. As I understand, if I import a WAV/FLAC of a song and only use cut, copy, delete, paste, trim, and do nothing else (no volume changes, no FX), I can safely export the file to the exact same sample rate and bit depth (e.g. 44.1 khZ / 24-bit) as the original file, and the end result will be lossless, correct? Do I need to apply dither in this case?

  2. By default, Audacity uses 32-bit float bit depth. Let’s say I have two files, 1st one is 16-bit, 2nd one is 24-bit. I’m not doing anything else than cutting, copying, deleting, pasting, trimming to these audio files. When exporting them, to the exact same bit depth, do I need to dither because Audacity is in 32-bit and the files are in lower bit depth? Should I change the Audacity settings to either 16-bit or 24-bit respectively before importing those files?

  3. Is Repair tool “destructive”? Meaning that there will be some quality loss? If it is, then I’m fine with that because I would use it to remove unwanted cracks and pops on my vinyl rips. Because the Repair tool will be altering the audio file, I need to apply dither, even when I’m not changing the bit depth, correct?

  4. If I use “Split Stereo to Mono” and then export only mono left or mono right channel (I delete the channel I don’t need) without doing anything to it - is the exported file still lossless?

  5. Let’s say that the right channel has reverb only. I use “Split Stereo to Mono”, then I select and invert this channel - now, when I play both channels together, the end result is that this technique reduces the overall level of the reverb of the left channel due to phase cancellation (that’s what I want). If I understand correctly, this is not lossless anymore, right? So it means when I export the WAV (Audacity mixes it as a mono before exporting), is it still lossless? Do I need to dither even if I export to the same bit depth?

Thanks in advance!

Audacity normally works internally at 32-bit floating-point. The conversion from 16 or 24-bit integer to floating-point and back is lossless.

  1. As I understand, if I import a WAV/FLAC of a song and only use cut, copy, delete, paste, trim, and do nothing else (no volume changes, no FX), I can safely export the file to the exact same sample rate and bit depth (e.g. 44.1 khZ / 24-bit) as the original file, and the end result will be lossless, correct?

Correct.

Do I need to apply dither in this case?

No, and since dither “changes something” it’s not lossless.

You’re “supposed” to dither when you down-sample. (But not if you simply up-sample and then down-sample to where you were without otherwise changing anything.) Dither is added noise and it’s supposed to be preferable to the “natural” quantization noise. But, at 16-bits or better you can’t hear dither or the effects of dither (under normal-reasonable listening conditions) so it’s no big deal one way or the other. (At 8-bits you can hear quantization noise.)

  1. By default, Audacity uses 32-bit float bit depth. Let’s say I have two files, 1st one is 16-bit, 2nd one is 24-bit. I’m not doing anything else than cutting, copying, deleting, pasting, trimming to these audio files. When exporting them, to the exact same bit depth, do I need to dither because Audacity is in 32-bit and the files are in lower bit depth? Should I change the Audacity settings to either 16-bit or 24-bit respectively before importing those files?

Don’t change the settings, and you can turn-off dither.

  1. Is Repair tool “destructive”? Meaning that there will be some quality loss? If it is, then I’m fine with that because I would use it to remove unwanted cracks and pops on my vinyl rips. Because the Repair tool will be altering the audio file, I need to apply dither, even when I’m not changing the bit depth, correct?

Anything that changes the “data” is not lossless. But this kind of everyday editing is not considered “lossy” and of course if you remove a click or pop, that’s an improvement! (You don’t need to dither after using Repair.)

  1. If I use “Split Stereo to Mono” and then export only mono left or mono right channel (I delete the channel I don’t need) without doing anything to it - is the exported file still lossless?

Yes, that’s lossless.

  1. Let’s say that the right channel has reverb only. I use “Split Stereo to Mono”, then I select and invert this channel - now, when I play both channels together, the end result is that this technique reduces the overall level of the reverb of the left channel due to phase cancellation (that’s what I want). If I understand correctly, this is not lossless anymore, right? So it means when I export the WAV (Audacity mixes it as a mono before exporting), is it still lossless? Do I need to dither even if I export to the same bit depth?

Again, anything that changes the data is not lossless. And this inversion/subtraction technique will generally have unwanted side effects. If left & right are identical except for the reverb (unliklely) you can kill the channel with reverb and make a mono file (which will play through both speakers).

A couple more thoughts…

because I would use it to remove unwanted cracks and pops on my vinyl rips.

There are specialized applications for cleaning-up vinyl. [u]Wave Corrector[/u] is fully-automatic and FREE. I’ve also used [u]Wave Repair[/u] ($30 USD) which is "manual’ like Audacity’s Repair effect. But it has several different repair methods and usually you can get an audibly perfect click or pop removal.

You can use Audacity’s Click Removal and or regular Noise Reduction for low-level hiss. But you have to “be careful” with any automatic noise reduction/filtering because there can be side effects and sometimes "the cure is worse than the disease". That’s the advantage of the manual methods… They only touch the audio where you identify a defect. And, sometimes I’ll just apply noise reduction during the fade-ins and fade-outs where the noise is most noticeable.

Although Normalization (volume adjustment) isn’t mathematically lossless, it’s considered lossless and it doesn’t hurt the sound. Rather than trying to get the “perfect” recording level, it’s actually better to leave some headroom (for unexpected peaks) and then boost the volume digitally after recording. The LAST thing you want is to record “too hot” and clip (distort) the audio!

A lot of older records are a bit dull sounding (rolled-off high frequencies) and in that case I’ll use a little equalization to boost the highs.

If you want to add album artwork to your files, Audacity can’t do that. I use MP3Tag (which works with most digital formats, not just MP3s).

One more thing about dither… As I mentioned, dither is nose and since vinyl noise is way “worse” than the dither noise you can consider it “self- dithered” and adding the dither won’t make any difference. That’s generally true of ANY analog source… There is usually more “analog noise” than dither (unless you are making 8-bit files).

P.S.
Don’t get too hung-up about lossy/lossless!
The usual idea of lossless audio is to have confidence that the audio hasn’t changed. But if you’re editing you usually WANT something changed. Professional audio production involves LOTs of technically-lossy (irreversible) processes and most of the changes are good!!!

Lossy file compression (MP3, etc.) is a different story. A good quality (high bitrate) MP3 can often sound identical to the uncompressed original but ALL of the “data” is changed (and most of the data is thrown-away) and sometimes you can hear compression artifacts. If you open an MP3 in Audacity (or any “normal” audio editor) it gets decompressed. If you then re-export as MP3 you are going through another generation of lossy compression and some “damage” does accumulate. If you want MP3 (or other lossy format) you should compress ONCE as the last step after all other editing.

Thank you so much for taking your time to write such a detailed reply, DVDdoug! I don’t have any more questions as your answers explained everything very clearly. Thanks.