Envelope tool and preserving quality

[KlarkKentThe3rd]

I have been struggling with about 40 tracks with bad fade-outs (they just do not dissolve into complete silence). I tried all adjustable fade options, and none worked perfectly (because I am not applying a fade-out; just trying to fix an existing one). And then I discovered the Envelope tool and finally it seemed I found the perfect solution.

But perfect solutions lead to further questions. I am well-aware that changing the volume of a 16 bit track requires dithering to preserve quality. But I don't want to touch the rest of he track; only the part of the fade-out I want to fix.

In other words: how to use the Envelope tool without changing or manipulating the parts of the track that are just fine? Let's say I have a 3 minute song. I want to use the tool on the last 10 seconds. How to leave the previous 170 seconds untouched?

[kozikowski]

Is the original work in MP3?
Koz

[KlarkKentThe3rd]

Is the original work in MP3?
Koz

I converted all the files into WAV, so no.

[steve]

I converted all the files into WAV, so no.

If you converted them from MP3 (or other lossy format) to WAV, then they are still essentially "MP3 quality". I'm not saying "poor" quality - MP3s can sound very good, but still we're not talking about "pristine" quality. Converting to WAV cannot restore the quality of an MP3 back to how it was before it became an MP3. The effect of dither is likely to be insignificant compared to the quality lost through MP3 encoding, so I wouldn't worry about it. Normal signal level is several thousand times bigger than dither - it's like whispering next to a rock crusher. Just apply the effect to the part that you want, check it sounds OK, export it (preferably in a lossless format), check the exported file and if it sounds good you're done.

[steve]

Oh yes, and ensure that you are using the current version of Audacity (2.0.5). There was a problem in some older versions where the dither noise could sometimes be a bit higher than it should be.

[kozikowski]

Slippery words.
You converted all the MP3 files into WAV?
Koz

[KlarkKentThe3rd]

Yes, I converted a lossy format (NOT em pi three) to WAV.

But when I mentioned quality I meant "not dithering the part that sound fine". Can I apply the Envelope tool to just one small section, and leave the rest of the track untouched? Not modified or dithered?

[steve]

Provided that you are working in 32 bit float format, dither is only applied on export.
On export, dither is applied to the entire track.

If you prefer, you can turn dither off altogether (Edit > Preferences > Quality: High quality conversion settings). You may find that interesting to do as an experiment - it does not make much difference.

I understand what you are getting at, it's something that I wondered about too. I did some experiments in which I applied dither only to certain parts (fade outs) and not to the rest. What I found was: I could not hear any difference at al between the two. The only time that I could hear any difference was if dither was "turned on" during a very quiet section - in this case the "turning on" was more obtrusive than it being on all the time.

Can I apply the Envelope tool to just one small section, and leave the rest of the track untouched? Not modified or dithered?

Yes you can. It may be worth doing as an experiment, but I would certainly not bother for any practical purpose.

1) Import the file.
2) "Edit > Preferences > Quality: High quality conversion settings" set dither to none.
3) From the track drop down menu, set the sample format to 16 bit.
4) Edit > Preferences > Quality: High quality conversion settings" set dither to "shaped".
5) Apply the fade effect (must be an "effect" NOT the Envelope tool).
6) "Edit > Preferences > Quality: High quality conversion settings" set dither to none.
7) Export (lossless format)
8) Edit > Preferences > Quality: High quality conversion settings" set dither to "shaped".

[KlarkKentThe3rd]

Apply the fade effect (must be an "effect" NOT the Envelope tool).

But I don't want to apply a fade effect. I tried it, and it is too noticeable. I want to use Envelope, but without modifying the entire track. You said it can be done.

[steve]

I want to use Envelope, but without modifying the entire track.

It can still be done, but it gets more complicated.

1) Import the file
2) select the part that you want to apply the envelope tool to.
3) Duplicate that part onto a new track. (Ctrl+D)
4) Delete that part from the original track
5) Apply the envelope to the duplicate
6) Ensure that dither is enabled for high quality conversion.
7) With the duplicate track selected, "Tracks menu > Mix and Render"
8) From the track drop down menu, set the sample format to 16 bit (this will apply the necessary dither).
9) "Edit > Preferences > Quality: High quality conversion settings" set dither to none.
10) Select all of the silence in the duplicate track.
11) "Edit menu > Remove Audio or Labels > Silence audio" (Ctrl+L). This will remove unwanted dither from the silence.
12) Export to 16 bit WAV
13) Edit > Preferences > Quality: High quality conversion settings" set dither to "shaped".

but as I said, it's really not worth the effort other than as an academic exercise.