Here is a compiled table of recommended bitrates for phycoacoustical
compression of audio that is derived from
- Compact Disks
- FM Radio, Analog Tape & LPs
- Speech sources
Raw bitrates (32 kbs, 56 kbs, 192 kbs etc...) as a measure of the
quality of encoded phycoacoustically compressed audio are a poor source
of reliable information.
- The sampling rate of the incoming audio can be at (8000 Hz, 22050
Hz, 32 kHz, 44.1 kHz, 48 kHz, 96 kHz etc ...).
- One can also resample from one digitization rate to another (48
kHz to 44.1 kHz is quite common).
- The incoming audio itself may be encoded at bit depths of either
8 bits, 16 bits, 24 bits or 32 bit integers -- as well as 32 bit
floating point.
- In some cases the incoming sampling system may be signed or
unsigned, as with mu-Law or A-Law sources related to telephony.
- Even digital origin sources may have been thru a phycoacoustical
encoding stage at some earlier point, leading to generational coding
issues.
- Variable Bitrate Coding (VBR) can also produce quite varied audio
output quality if one does not take care to learn the behaviors of the
encoder.
- Magnetic tape and vinyl audio sources have tape hiss and source
rumble -- as well as wow and flutter. A sampling rate that is too low
coupled with a bitrate that is too low can lead to these noise sources
becoming overpowering.
- Analog recording artifacts in general can produce substantial
distortion if not factored into the digitization process.
- Analog sources, namely 16 mm and 32 mm film and Dolby encoded
magnetic tape can produce dynamic range compression and failed
decompression artifacts if not put thru the proper decoder.
Source : CDs and DVDs (True Stereo [DDD], 20hz-20khz)
Compression Format
|
Musicam (MP2)
|
MP3
|
Ogg Vorbis |
MP3 Pro |
AAC
|
AAC + SBR
|
| Lowest Bitrate |
192 kbs
|
128 kbs
|
112 kbs
|
92 kbs
|
80 kbs
|
80 kbs
|
Highest Bitrate (best)
|
256 kbs
|
160 kbs
|
128 kbs
|
112 kbs
|
128 kbs
|
128 kbs
|
VBR "best effort"
|
= NA =
|
[80...128] kbs
|
= NA =
|
[80...128 kbs]
|
[60...112] kbs
|
[60...112] kbs |
Source : FM Radio, Analog Tape & LPs (Joint Stereo or Matrix
Stereo, [AAD] or [ADD], 20hz-16khz)
Compression Format
|
Musicam (MP2)
|
MP3
|
Ogg Vorbis |
MP3 Pro |
AAC
|
AAC + SBR
|
| Lowest Bitrate |
112 kbs
|
92 kbs
|
92 kbs
|
80 kbs
|
60 kbs
|
60 kbs
|
Highest Bitrate (best)
|
128 kbs
|
128 kbs
|
128 kbs
|
92 kbs
|
112 kbs
|
92 kbs
|
VBR "best effort"
|
= NA =
|
[80...128] kbs
|
= NA =
|
[80...128 kbs]
|
[60...112] kbs
|
[60...112] kbs |
Speech sources : MW Radio, Talking Books (Parametric Stereo, [AAA],
120hz-12khz)
Compression Format
|
Musicam (MP2)
|
MP3
|
Ogg Vorbis |
MP3 Pro |
AAC
|
AAC + SBR
|
| Lowest Bitrate |
48 kbs
|
32 kbs
|
32 kbs
|
32 kbs
|
28 kbs
|
28 kbs
|
Highest Bitrate (best)
|
60 kbs
|
48 kbs
|
48 kbs
|
48 kbs
|
48 kbs
|
92 kbs
|
VBR "best effort"
|
= NA =
|
[16...48] kbs
|
= NA =
|
See MP3
|
[16...28] kbs
|
See AAC
|