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During the audio encoding process for analog modem delivery, your sound files go through drastic changes as bits of data are thrown out and compressed to reduce file sizes. This process eliminates certain frequencies and accentuates background noises that you may not have noticed in the original audio source. Generally, the two areas to focus on are the highest ¼ of your audio frequencies and the lowest ¼ of your audio frequencies. The higher frequencies (above 10,000Hz) tend to carry a lot of background noise, such as hiss and scratchiness in an audio file. Whereas the lower audio frequencies (below 75Hz) tend to carry a lot of the rumble that can occur from background noises, such as H/VAC systems or microphone rumble caused by wind.
To correct this problem, eliminate the low-end frequencies between 20Hz and 75Hz and the highest frequencies above 10,000Hz with the equalization faders in your sound editor. Then boost the low-end bass frequencies between 75Hz and 110Hz to compensate for the elimination of the bass sounds below 75Hz. It's also a good idea to boost the mid-range vocal frequencies between 2,000Hz and 7,000Hz to add brightness to a mix and make the vocals clearer after Web conversion, as shown in Figure 1.
It seems this tutorial is aimed at very low bitrate compression, for 56k modem streaming. Dismiss the
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