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In converting your MP3's the data rate governs the quality of the MP3 when
played back. The higher the data rate, the more information from the original
track can be stored and a better quality playback is achieved.
If your music is to be played back via headphones and computer, we recommend
at least 192. For higher quality Hi-Fi we strongly recommend 192 or above.
1. The higher the bit
rate, the better the sound quality (and size) of the resulting file. Lower the
bit rate, and your sound quality goes down. But your file sizes go down too.
Depending on your particular needs, you can move off the benchmark of 128 kbps.
You can go higher than 128 kbps for less compression and even better sound
quality. Or you can lower the bit rate to further shrink the size of your mp3
files. Of course, sound quality will suffer the lower you go, but you can get
some amazingly small files in the process.
The table below can help you estimate the kind of mp3 quality/compression and
bit rates to use for your own applications. We also give you approximate file
sizes to help you compare.
| Format |
Bit rate |
File size
per minute |
Min per GB |
Notes |
| CD
or WAV |
Uncompressed |
10
MB |
100
Mins |
If
the wave wav file was sampled at 16 bits/44.1kHz, you've got CD quality
sound |
| MP3 |
320
kbps |
3.0
MB |
333
Min |
Very
low compression, superior sound quality - We recommend |
| MP3 |
192
kbps |
1.8
MB |
555
Mins |
The
standard "CD quality" bit rate |
| MP3 |
160
kbps |
1.5
MB |
666
mins |
Very
low compression, superior sound quality |
| MP3 |
128
kbps |
1.0
MB |
1000
Mins |
The
standard "CD quality" bit rate |
Anything below 128 kbps is going to affect
your audio quality, but you might want to experiment and see how low your
file sizes can go. For instance, you'll be surprised at how well
"voice only" audio can sound at the lower bit rates.
Constant bit rate vs. Variable bit rate
To further complicate the bit rate game, many encoders allow you to
customize the encoding process by selecting either constant or variable
bit rates.
Constant Bit Rate encoding (CBR) maintains a steady bit rate stream
through the entire mp3 file. This means a consistent level of compression
and predictable file sizes. CBR has also been around longer, and is
supported by all MP3 players. It's the safe, reliable, consistent route to
take when in doubt. Settings range from 16 kbps to 320 kbps depending on
the file size you're targeting. Remember that files encoded faster than
128 kbps may have little or no detectable improvement in sound quality.
CBR has its drawbacks, especially when encoding certain kinds of music.
Consider this rhetorical question: is your music always consistent in
terms of dynamic range, complexity, polyphony, and stereo separation? Many
times, a single piece of music will vary some or all of these qualities.
Some passages are complex, some are silent with narrow stereo separation;
other passages are dense, complex, and busy with wider stereo separation.
And yet, Constant Bit Rate encoding pays no mind to all that and keeps its
bit rate steady as she goes. You run the risk here of using more bits than
is necessary for the music's quiet parts, and not enough bits than you'd
optimally want for encoding for the busier, more dense musical sections.
What can happen (experiment with CBR encoding to see if you can hear it)
is that the complex/difficult parts don't sound as good as other parts of
the music. On the flip side is the impact of things you can't hear: the
wasted bits encoded during the simpler, quieter sections.
Which brings us to rule of thumb number two:
2. Constant bit rate encoding = consistent, limited file sizes but
variable sound quality.
To address the shortcomings with constant bit rate encoding, Variable bit
rate encoding (VBR) was developed. VBR is newer than CBR; most mp3 players
don't support VBR…yet. The most recent upgrades to FreeAmp, Winamp, and
MusicMatch support it. And the Xing encoding program supports it too.
If you seek consistently high audio quality, and file size isn't as much
of a concern, you should consider using it. VBR makes intelligent
decisions before allocating its bits to the encoding process. It adapts
the bit rate to the complexity of the audio, based on a scale you can set
in the preferences of your encoder. The low end of a scale from 1 to 100
would result in the lowest quality/highest compression. The high end of
the scale would result in the highest quality/lowest compression. The
results? Overall, you'll get better and more consistent sound quality
compared to CBR encoding at the same bit rate.
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