PROFESSIONAL SOUND PROGRAMMING ON THE ST by Holger Gehrmann
The fashion of programming complex pieces of music on home
computers started already at the very beginning of home
computing, when the VIC 20 from Commodore hit the market. The
soundchip has one noise-and three tone generators, that could
only produce a pulse waveform. The volume could only be
controlled for all tone generators at once. The idea of
programming complex musical compositions didn't even find its
origin then, because the musical capabilities were simply too
All changed when the Commodore 64 appeared. And already two years
after its launch, very complex songs were finding their way to
the users which were packed with sound effects. No wonder: The
sound capabilities of this computer could easily match those of a
small and cheap synthesizer system.
One would think that a new computer like the Atari ST should even
outdo the sound possibilities of the 64, but the ST unfortunately
contains a regular Yamaha chip. It offers three pulse tone
generators, to which noise can be mixed individually. The volume
can be defined for every voice independently (that is quite an
advantage). Except for these, a kind of waveform also is
implemented, that can not be used properly.
The musical qualities of the ST are thus significantly less than
those of the Commodore 64. The tone reproduction, however, is
better: The SID of the 64 works analogue (so there'll be more
ground noise), whereas the Yamaha chip of the ST works digital
(which takes care that a clearer note appears).
After programming many songs on the VIC 20 and Commodore 64, I of
course wanted to expand my sound programming experience to the
ST. Since I had already programmed small test-compositions on
the Amstrad (which has the same soundchip), it wasn't that
difficult to re-program my soundtool for the ST. But I did want
to build in a few extra options into my soundtool (which I, by
the way, called SOund PROgramming Language) that would allow some
extra sound effect possibilities.
The following sound effects can be established:
The GLIDE effect:
The current note is continually increased and decreased.
The MODULATION effect:
The current note is increased and than decreased all the time.
This produces a kind of VIBRATO, which makes the very 'flat' note
of the ST sound a bit 'weaker'.
The DOUBLE-TONE mode:
This takes care that two different notes are toggled using only
one tone generator. This creates the impression that one sound
generator becomes two sound generators. The use of chords is much
easier this way, and doesn't use that much sound generators.
The BEND effect:
The next note is not directly played, but the program starts from
the last played note and then increases/decreases to the current
note (a bit like the GLIDE effect). This is often used with
This is much alike the MODULATION effect, but here the volume is
continually increased or decreased.
The TWO-VOLUMES mode:
Much like the DOUBLE-TONE mode, but here the volume is toggled
between two values continually.
The NOISE-GLIDE effect:
This sound effect is just like the GLIDE effect, but this time
the noise genarators that can be mixed into the sound are
increased and decreased all the time. This effect can very well
be used to imitate drumming sounds.
Even with all these features, a proper tone quality cannot be
reached. That's why I simulate the on the Commodore 64 so well
known waveform generator (ADSR). With SOPROL, this functions much
like that on the 64, but I included an additional option: The
Attack-, Decay-, Sustain-and Release TIME is not the only
variable thing, but it's also possible to specify the step size
of those. This feature makes it easy to program alienating
The last problem is the use of the sound data in the source code.
Since I only work with the K-Seka assembler from Kuma, this whole
business became a bit tough, also because Seka doesn't offer that
SOPROL controls every byte that it reads, to check if it's larger
or equal to $F0. If it is, that means that is has encountered a
The commands are:
$F0 JUMP Jump to another position of the song
$F1 CALL Call a sound-subroutine (e.g. if a part of a song
has to be used several times)
$F2 RECALL Jump back from a sound-subroutine
$F3 CHANGE Change the sound effect settings
$F4 NOP No operation
When the byte that was read comprised no command, SOPROL checks
if the byte is larger than $C0. If so, that means that the
current tone-length has to be changed. The new tone-length can be
calculated by: Length=Byte-$C0.
Whenever the byte that was just read is smaller than $C0, SOPROL
knows that an actual note is meant here. The high-nibble
comprises the octave and the low nibble the tone you wish.
Since SOPROL works on Interrupt (using the Vertical Blank
Interrupt queue, ED.), the main program has to write a certain
value on a certain memory location (I call this SONGFLAG most of
the time). The song corresponding with that number will be played
until the value 0 is stored on SONGFLAG.
The first time I used SOPROL on the ST, I used it in my program
called "Extensor", which features five different songs. The next
program I used it for was "Hollywood Poker". Both programs were
published through Golden Games, which I owned for 50% until
recently. Since I retreat from this company and will be running
my own software company called "ReLINE Software", only programs
from "ReLINE" will feature SOPROL songs in the future.
I hope to have stimulated you to program sound on the ST by means
of this article. Professional music is not only possibile through
MIDI, but can also be used if one works good enough with the
generators of a sound tool or so.
Holger Gehrmann is a guy that programs software for Amstrad,
Commodore 64, Commodore Amiga, Atari ST and no doubt several
other computers. It is amazing that he does things like this with
the means he has (remember? He only uses K-Seka!). I hope he will
continue this article in the future, in which he will then
explain the specific routines, etc. But that's not sure. Anyway,
he will soon supply us with some pieces of music that can be
included into our Synth Sample V...
The text of the articles is identical to the originals like they appeared in old ST NEWS issues. Please take into consideration that the author(s) was (were) a lot younger and less responsible back then. So bad jokes, bad English, youthful arrogance, insults, bravura, over-crediting and tastelessness should be taken with at least a grain of salt. Any contact and/or payment information, as well as deadlines/release dates of any kind should be regarded as outdated. Due to the fact that these pages are not actually contained in an Atari executable here, references to scroll texts, featured demo screens and hidden articles may also be irrelevant.