Selecting The Data Output Rate - Commodore Amiga Hardware Reference Manual

Table 5-2: Volume Values
Volume Decibel Value
64 0
(maximum volume)
48 -2.5
32 -6.0
16 -12.0
(12 db down from the
volume at maximum level)
For any volume setting from 64 to 0, you write the value into bits 5-0 of AUDOVOL.
For example:
SET AUDOVOLUME: MOVE.W #48, AUDOVOL
The decibels are shown as negative values from a maximum of 0 because this is the way
a recording device, such as a tape recorder, shows the recording level. Usually, the
recorder has a dial showing 0 as the optimum recording level. Anything less than the
optimum value is shown as a minus quantity.
SELECTING THE DATA OUTPUT RATE
The pitch of the sound produced by the waveform depends upon its frequency. To tell
the system what frequency to use, you need to specify the sampling period. The sam-
pling period specifies the number of system clock ticks, or timing intervals, that should
elapse between each sample (byte of audio data) fed to the digital-to-analog converter in
the audio channel. There is a period register for each audio channel. The value of the
period register is used for count-down purposes; each time the register counts down to 0,
another sample is retrieved from the waveform data set for output. In units, the period
value represents clock ticks per sample. The minimum period value you should use is
124 ticks per sample and the maximum is 65535. For high-quality sound, there are other
constraints on the sampling period (see the section called "Producing High-quality
Sound "). Note that a low period value corresponds to a higher frequency sound and a
high period value corresponds to a lower frequency sound.
140 Audio Hardware