Encoder Options for aac / m4a Files
Here you can choose how you would like the audio to be compressed inside the m4a file. AAC is a "lossy" format and will provide a higher degree of compression at the expense of some quality (similar to mp3). ALAC is a "lossless" format which guarantees no quality loss, but can't compress your file as much.
Here you can select the sample rate to use for the output file. A higher sample rate will generally result in better quality output, but only if the files which make up your project were also recorded at that same high sample rate.
This number describes how many bits of resolution each sample has. A higher number means a greater resolution. CD quality audio is 16 bits and is generally enough for most applications
This selects whether the output file will be Mono or Stereo (one channel or two channels respectively).
Average Bitrate Encoding (ABR)
Select this option to encode the audio using an average bit rate. The specific bitrate value can be selected from the bitrate drop-down list.
Variable Bitrate Encoding (VBR)
Select this option to encode the audio using a variable bit rate, which is considered to produce superior results to ABR encoding. For this mode you only need to select a Quality value from the respective drop-down list. Values range from 10% to 500%, with higher values producing higher quality audio and a larger output filesize.
The advanced options box gives a choice of encoding options that are not normally used for encodings, but may be of value to advanced users who understand the complexities of the format. The options are presented as below.
Advanced Options - Force MPEG2 Output
Forces encoding using AAC MPEG2 audio (if not checked the default is AAC MPEG4 audio)
Advanced Options - Disable Temporal Noise Shaping
Disables usage of Temporal Noise Shaping, a feature that may or may not produce better sounding output audio.