Questions about maintaining audio quality when exporting

First off, this is the audio file I’m working with:

Audio: AAC 48000Hz stereo 105kbps [A: aac he-aac, 48000 Hz, stereo, 105 kb/s]

Format: ADTS
Format/Info: Audio Data Transport Stream
File size: 16.0 MiB
Overall bit rate mode: Variable

Format: AAC
Format/Info: Advanced Audio Codec
Format version: Version 4
Format profile: HE-AAC / LC
Bit rate mode: Variable
Channel(s): 2 channels
Channel positions: Front: L R
Sampling rate: 48.0 KHz / 24.0 KHz
Compression mode: Lossy
Stream size: 16.0 MiB (100%)

What I want to do is some minor trimming and a fade out effect, and then export it again, preferably as an AAC file. However, when I export it as M4A/AAC, there’s a quality scale from 10-500, and regardless of what I choose, it seems like the final product is a constant 198 Kbps rather than being variable. So I’ve got 2 questions:

  1. Is constant 188 Kbps a good thing or a bad thing? I can’t help but notice it’s higher than the variable 105kbps of the original file and as a newbie I have no idea what that means or how much better/worse it is compared to the original file.
  2. Am I on the right track for exporting an audio file that’s as comparable to the original in terms of quality? If not, can I get some advice on a better way of going about it?

If your original is from a compressed format, your only choices are The Same Quality and Worse. The only way to get The Same Quality is export the work as an uncompressed sound file such as Audacity default WAV (Microsoft) 16-bit. All the other options produce additional compression damage. Depending on the length of the show, the WAV file size will go through the roof.

You’re not compressing to 198 (or 188). Since you’re starting with a 105 compressed file, the export will be the combination of 105 and 188, something worse than 105. If you try to go back to 105, you could get a compression quality of 60.

You can minimize that damage by using the highest re-compression quality you can get. That will give you not too much worse than 105.

There are editors which allow you to do simple editing like your trims and cuts without changing the compression damage. But not fades. Fades require re-compression.

So that’s your Google search term.

If you are using FFmpeg for Audacity 2.1.2, that’s the latest and greatest version. We don’t write FFmpeg, so we need to wait for another elf to see what could be wrong.


The slider does not work with the FFmpeg build that we recommend. See for explanation and workarounds.

Because Audacity must re-encode, matching the bit rate of the original will make the sound worse than if you maximised the bit rate (which would just make it slightly worse). Give you don’t want to apply filters, you should be able to use Macsome to make your edits losslessly (note I have not tried it, I just go on what it says).


Try [u]MP3DirectCut[/u]. It can do limited editing on MP3 & AAC files without de-compressing/re-compressing.

Oops I thought FMPIV was on Mac. Sorry. If you have MP4/M4A files, MP3DirectCut requires you to extract the audio to raw AAC, then convert back.

There is a free trial of MP3 True Edit which also claims AAC support.


Thank you for the informative replies. I’m very stubborn about the fades so programs that allow for limited editing don’t work. If I do the fade with Audacity, export it as a WAV, and re-compress that WAV to an AAC file with iTunes (stereo 320 kbps, variable bit rate encoding), would the resulting file be somewhat close to the original 105? Just want to confirm this one point. If that would still be significantly worse then I’ll probably compromise and take up the suggestion of just doing limited editing.

The applications we mention do allow fades. Have you tried them? But you can’t for example change the equalization with those tools.

Yes, reasonably close, but only you can judge based on the material. The file will be larger than before and it will not be a lossless edit that you could do in the other applications.


You don’t have a song. You have a song plus 105 damage. If you make a WAV, the WAV will have the song plus 105 damage in perfect quality and large filesize. If you then go back down again, you’re going to be compressing the song plus compressing the 105 damage.

You don’t have the original song. The ability to back out of a compression scheme to the original perfect quality music is frequently requested.

The best way to avoid additional damage is recompress at the highest possible quality. If the tools give you the option of 500 quality, use that, but the files are going to be quite a bit larger.

If I’m forced to do this with with MP3, I use Audacity’s highest export quality which I think is 320. Otherwise I go right to WAV. WAV has a quality value too, I think it’s something like 1500.

Compressed files are end products for your iPod, not steps in the middle of production. Everybody gets burned with this.


Stereo WAV quality (44100, 16-bit) is a bit over 1400. Forgive me. I had to go back to an earlier machine. The newer tools don’t tell me that value.