Psg instruments

Por PingPong

Prophet (3460)

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15-10-2019, 14:29

Time ago i have found a music composer for msx. On the menu there was a choice betweeen various musical instruments.
But afaik i only know two instruments doable with psg: piano (or bell) and organ.

Are there others?

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Por JohnHassink

Ambassador (5417)

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15-10-2019, 19:39

Our sweet little MSX PSG does not have any 'instruments' to speak of. At default, it generates a plain square wave, which we can influence using 'software voices'. This particularly means using volume and tone offsets (think ADSR envelopes) to simulate the timbre of certain actual instruments.

It also has 8 different 'hardware voice' presets, which allows us to change the square wave into a sawtooth or a triangle. It cannot generate sine waves.

Technically, you may regard the PSG as a very, very rudimentary synthesizer.
But if you want a more visual idea, imagine 3 straight flutes, or organ pipes, of which you can non-permanently cut the tubes in different shapes to modify the way the sound comes out.
Ofcourse, with an additional white noise generator, but I think that's a bit less relevant here.

Now, some music programs may come with ready to use presets which shape the sound using a software envelope and/or a hardware envelope.
Ofcourse said presets need to have names (which would usually be something which their resulting sound kind of approaches, like a "piano" or a "violin" or a "snare drum"), but nothing as such is already internally present in the actual chip.
So, sure, for example we can create:

  • A staccato sound, which comes up quickly and fades off relatively early again, and call that "Harpsichord"
  • A sound that gradually swells on to be louder and results in a bit of frequency modulation, and call that "Violin" or "Slow Strings"
  • A sound that rapidly pitches downwards tone-wise, accompanied with some crashing white noise, and call that "Snare Drum"

...etcetera, etcetera, but it will only approach such a sound, or the name simply serves to differentiate the 'instruments' that we can use.

The PSG is far from being like an FM-PAC or an OPL4 - it does nothing "by itself"; you have to tell it exactly what to do. The same is actually true for SCC, but that's a different story.

I hope this answers your question.

Por PingPong

Prophet (3460)

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16-10-2019, 13:35

thx, but,

Quote:

The PSG is far from being like an FM-PAC or an OPL4 - it does nothing "by itself"; you have to tell it exactly what to do. The same is actually true for SCC, but that's a different story.

OK, this was already clear to me, but my question was more like ' i haven't heard nothing similar to a violin from PSG', anyone know what types of instruments we can throw out from the PSG by altering volume, tone, hw envelope frequencies and wave forms? Is there anyone that got a violin or somewhat instrument from the PSG? While a organ was simple i cannot see how a violin could be simulated.
if the PSG was able to do sinusoidal waves and have a lot of channels a good choice of instruments could have done but with a square wave only....

Por JohnHassink

Ambassador (5417)

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16-10-2019, 16:33

I don't think a PSG can actually sound like an organ, either. It's just a matter of perception.

Por zPasi

Champion (474)

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17-10-2019, 07:30

JohnHassink wrote:

I don't think a PSG can actually sound like an organ, either. It's just a matter of perception.

More complex "instruments" are done by software. Add some vibrato and modulation in a tracker (e.g. Arkos 2) and you almost get an organ.

Por Grauw

Ascended (8515)

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17-10-2019, 08:15

I guess the basis of an organ sound is chords of overtones (e.g. base + a fifth + an octave), even if you're working with square instead of sine waves. It costs you all three tone channels though so if it's really practical...

Por DarkSchneider

Paladin (880)

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17-10-2019, 11:02

The problem of the Envelop Generator is that it works at different scale than tone generator, so it is not easy to make them work together as wanted.

Por zPasi

Champion (474)

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17-10-2019, 11:19

Grauw wrote:

I guess the basis of an organ sound is chords of overtones (e.g. base + a fifth + an octave), even if you're working with square instead of sine waves. It costs you all three tone channels though so if it's really practical...

Yeah. A single tone "organ" done with PSG is kinda thin, of course. With 3 PSGs you could do an organ with overtones and three voices, to play triads Smile2 Even less practical.

DarkSchneider wrote:

The problem of the Envelop Generator is that it works at different scale than tone generator, so it is not easy to make them work together as wanted.

I don't know, I just let Arkos 2 do its magic Wink

Por Grauw

Ascended (8515)

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17-10-2019, 11:34

DarkSchneider wrote:

The problem of the Envelop Generator is that it works at different scale than tone generator, so it is not easy to make them work together as wanted.

The envelope generator does go into audio range, but the period is specified as 1/16th of the tone generator. This also means that the envelope generator range is 4 octaves less than the tone generator, so it works best for low tones and you get into serious precision problems above the middle A, the pitch will be out of tune and certain notes can’t be played at all.

If you want to combine the envelope and tone generators to make more complex waveforms (through ring modulation), just make sure to set the tone period to 16 times the envelope period and keep the bottom 4 bits zero. Also briefly set the tone period to 0 prior to note-on to make sure they sync consistently. If you use the exact tone period or set some of the bottom 4 bits their frequencies will desync and the timbre will be beating (pulsating), this may or may not be an effect that you want.

I wrote more about it here. Also I made a video experimenting with it.