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Producing High-quality Sound
When trying to create high-quality sound, you need to consider the following factors:
o
Waveform transitions.
o
Sampling rate.
o
Efficiency.
o
Noise reduction.
o
Avoidance of aliasing distortion.
o
Limitations of the low pass filter.
MAKING WAVEFORM TRANSITIONS
To avoid unpleasant sounds when you change from one waveform to another, you need
to make the transitions smooth. You can avoid "clicks" by making sure the waveforms
start and end at approximately the same value. You can avoid "pops" by starting a
waveform only at a zero-crossing point. You can avoid "thumps" by arranging the aver-
age amplitude of each wave to be about the same value. The average amplitude is the
sum of the bytes in the waveform divided by the number of bytes in the waveform.
SAMPLING RATE
If you need high preCISIon in your frequency output, you may find that the frequency
you wish to produce is somewhere between two available sampling rates, but not close
enough to either rate for your requirements. In those cases, you may have to adjust the
length of the audio data table in addition to altering the sampling rate.
For higher frequencies, you may also need to use audio data tables that contain more
than one full cycle of the audio waveform to reproduce the desired frequency more accu-
rately, as illustrated in figure 5-4.
152 Audio Hardware
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