Each audio channel includes an eight-bit digital-to-analog converter driven by a direct
memory access (D11A) channel.
The
audio
D11A
can retrieve two
data
samples during
each horizontal video scan line.
For
simple, steady tones,
the
D11A can automatically
playa
waveform repeatedly; you can also program all kinds of complex sound effects.
There
are two methods
of
basic sound production on the Amiga - automatic (D11A)
sound generation and direct (non-D11A) sound generation. When you use automatic
sound generation,
the
system retrieves
data
automatically by direct memory access.
Forming
and
Playing
a
Sound
This
section shows you how
to
create a simple, steady sound and play it. Many basic
concepts
that
apply
to
all sound generation on the Amiga are introduced in this section.
To
produce a steady tone, follow these basic steps:
1. Decide which channel
to
use.
2. Define
the
waveform and create the sample table in memory.
3.
Set
registers telling the system where
to
find the
data
and
the
length
of
the
data.
4. Select the volume
at
which
the
tone is
to
be played.
5. Select the sampling period,
or
output
rate
of
the
data.
6. Select an audio channel and
start
up the
D11A.
DECIDING
WHICH
CHANNEL
TO
USE
The
Amiga has four audio channels. Channels 0 and 3 are connected
to
the
left-side
stereo
output
jack. Channels 1 and 2 are connected
to
the
right-side
output
jack.
Select a channel on
the
side from which
the
output
is
to
appear.
136 Audio Hardware
To Next Page
Loading...
