R.Schrijvers, 00-00-00
This is the English version of a Dutch article that will be published in MCCM
70 and on Sunrise Magazine #14.
M O O N S O U N D
===================
Almost one and a half year ago the Swiss MSX-Hndlergemeinschaft asked me to
write the software for the soundchip they were going to develop for MSX. They
had plans to build a cartridge with an OPL3 from Yamaha. The whole project
took some time so meanwhile Yamaha released the sequel: the OPL4! After
reading the OPL4 specifications I asked them to use the OPL4 in stead of the
OPL3 and fortunately they agreed. The name of this cartridge with OPL4 will be
Moonsound.
Unfortunately I didn't receive an OPL4 evaluation board yet but fortunately I
have had an OPL3 evaluation board for over 6 months now. This means that
everything in this text concerning the FM synthesizer has been tested by me,
but that everything concerning the PCM synthesizer comes from the Yamaha
manuals without testing.
To start I'll give a list of the most important possibilities of the chip.
I'll try not to get too technical, but sometimes this cannot be avoided
completely. Some experience with using MSX-AUDIO (Music Module) and
MoonBlaster will be of great help. The OPL4 has two main parts. An FM
Synthesizer Unit (the OPL3) and a PCM Synthesizer Unit. This last one is
better known in the PC world by the name Wave Table Synthesis.
FM:
- Upto eighteen 2-Operator FM channels or fifteen FM channels with five drum
sounds
- Upto six 4-Operator FM channels (together with another six 2-Operator
channels)
- Eight different waveforms
- Possibility to specifiy right, left or both for each channel
PCM:
- Upto 24 waves simultaneously! (this means 24 channels)
- Replayfrequency of 44.1 kHz
- 8, 12 or 16 bits wavedata
- Stereo signal in 16 positions for each channel
THE FM SYNTHESIZERS
The best way to judge the FM synthesizer of the OPL4 is by comparing it to
MSX-MUSIC (FM-PAC) and MSX-AUDIO (Music Module). The possibilities of these
chips should be known by everybody nowadays. The OPL4 resembles the MSX-AUDIO
the most. This is not so strange because the MSX-AUDIO is actually the OPL1.
The FM synthesizer of the OPL4 is 100% compatible with the FM synthesizer of
MSX-AUDIO. But the OPL4 has twice as many channels!
On top of that there are the so-called 4-Operator instruments. Normally an
instrument is created by adjusting two operators in the right way. Compare
this to the Make Own Voice part of MoonBlaster. Now it is also possible to
create voices using four operators. It speaks for itself that you can create
much better instruments than with only two operators. Another improvement is
that the waveform can be selected for each operator. On the MSX-AUDIO the
waveform is always a sinus, now that can be changed.
Finally a stereo possibility was added to the FM synthesizer. With MoonBlaster
we had to go through a lot of trouble using two different soundchips to get
stereo, now you can select for each channel if it should be heard left, right
or both.
THE PCM SYNTHESIZERS
This part of the OPL4 makes it possible to play samples. A sample is a piece
of digitized (sampled) sound. You can use this to get very realistic
instruments, because it's an exact copy! A drawback of samples is that a large
difference between the record and play samplefrequency will give bad quality:
the instrument doesn't sound like the original. To get a good piano for
example, it would be necessary to sample each note seperately. To prevent this
the sample will be influenced by the PCM synthesizer. A lot of things can be
done with this, a lot of them are also used for FM synthesis, like attack,
decay, etc. An extra advantage of this synthesizer is that the samples can be
short because, for example, the decay of the tone can be done by the
synthesizer. Playing a sample with these extra 'effects' is known as Wave
Table Synthesis and a sample with this extra information is called a 'wave'.
The quality of a sample is determined by two things: de sample resolution and
the sample frequency. With a sample resolution of 16 bits and a frequency of
44.1 kHz the OPL4 has sound of CD quality!
The PCM synthesizer has stereo possibilities too. These are even better than
those of the FM synthesizer, because here there is no left/right/both but a
real balance with 16 positions! This balance can be set for each of the 24
channels seperately.
PCM data takes a lot of memory, even with the synthesizer stuff of the OPL4.
Especially on an MSX it is not nice at all to load 300 kB of wavedata for one
song. The solution for this is the 2 megabyte ROM which will be in the
cartridge too. This ROM was designed by Yamaha especially for the OPL4 and it
contains all General MIDI sounds! These are 128 instruments and 47 drum
sounds. On top of that there will be 128 kB RAM in the cartridge so can you
can use your own samples too. For the real freaks it will be possible to
replace this 128 kB RAM by 512 kB RAM.
To erase any doubts: the OPL4 is not able to digitize sound, it can only
replay it. This is not really a problem because wavedata is just PCM data with
some extra information. It should be simple to use samples created by a Music
Module, turbo R or another computer.
SPEED
Programmers will be interested to know that the OPL4 is much faster than
MSX-MUSIC and MSX-AUDIO. Even the quite slow Z80 had to wait when accessing
those chips. But the OPL4 is so fast that even the R800 doesn't have to wait
anymore. Another advantage is that all (!) registers can be read.
It is a mayor advantage for the relatively slow MSX computer that the OPL4
handles almost everything itself. It would never be possible to play 24 waves
simultaneously if this hadn't been the case. Just think about the MODplayer by
XelaSoft. It takes all the CPU time on a turbo R to play 4 samples. The OPL4
makes it possible to create demos and games with fabulous background music.
The 128 kB RAM can be used perfectly for sound effects in games. It should be
possible to make a MODplayer for Z80 that leaves enough CPU time for other
programs to run simultaneously!
THE SOFTWARE
When you buy the OPL4 you'll get it with two music editors. Both of them are
special MoonBlaster versions. There is an FM version and a Wave version. The
FM version supports upto 18 FM channels in combination with 6 Wave channels
for drums. The Wave version will 'only' support the 24 Wave channels. There
are two versions to keep the songdata small and to let the programs run on
computers with 128 kB RAM.
Both programs will look a lot like MoonBlaster so everybody who is used to
those programs will get used to these new programs very soon. The main
advantage with MoonBlaster that these programs run under DOS. If there is a
memory mapper of 256 kB or more DOS2 (and harddisk) will be supported. It will
be possible to load MoonBlaster v1.4 songs in both programs.
As soon as these MoonBlasters are finished I'll start programming a General
MIDI file player and a MODplayer. I can't say when they will be finished yet,
but if everything is as easy as it looks from the Yamaha manuals it won't take
too long.
A lot of groups already announced that they will support the OPL4, on the
large International MSX fair in Tilburg (April 7th 1995) the first demos and
games with OPL4 music will be released.
Moonsound (the cartridge for MSX with OPL4) will probably be available in
October or November. The price will be approximately US$ 200. On the MSX fair
in Zandvoort on September 17th 1994 the exact price will be announced. Visit
the Sunrise stand for a demonstration of the OPL4. You can order Moonsound
there as well.
Remco Schrijvers
Translated by Stefan Boer
(c) Sunrise Foundation 1994
P.O. Box 178
1530 AD Wormer
Netherlands
E-mail: smboer@cs.vu.nl
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