Commodore Amiga A1000, Hardware Reference Manual

Page: 144 / 380

Sound data is organized as a set of eight-bit data items; each item is a sample from the
waveform. Each data word retrieved for the audio channel consists of two samples.
Sample values can range from -128 to +127.
As an example, the data set shown below produces a close approximation to a sine wave.
NOTE
The data is stored in byte address order with the first digitized amplitude value at the
lowest byte address, the second at the next byte address, and so on. Also, note that the
first byte of data must start at a word-address boundary. This is because the audio DMA
retrieves one word (16 bits) at a time and uses the sample it reads as two bytes of data.
To use audio channel 0, write the address of "audiodata" into AUD0LC, where the audio
data is organized as shown below. For simplicity, "AUDxLC" in the Table below stands for
the combination of the two actual location registers (AUDxLCH and AUDxLCL). For the
audio DMA channels to be able to retrieve the data, the data address to which AUDOLC
points must be somewhere in chip RAM.
Table 5-1: Sample Audio Data Set for Channel 0
audiodata ---> AUD0LC * 100 98
2 ** 92 83
4 71 56
6 38 20
8 0 -20
10 -38 -56
12 -71 -83
14 -92 -83
16 -100 -98
18 -92 -83
20 -71 -56
22 -38 -20
24 0 20
26 38 56
28 71 83
30 92 98
NOTES
* Audio data is located on a word-address boundary.
** AUD0LC stands for AUD0LCL and AUD0LCH.
- Audio Hardware 135 -