Jump to content
  • 0

How do you use vera's psg?


lamb-duh
 Share

Question

The waves available (triangle, sawtooth and square) all have lots of overtones, which make them inappropriate for additive synthesis (I think?), but there's no phase shift which makes it impossible to do subtractive synthesis (I think?). The only thing that's left is the pulse width modulation controller, but I don't understand how it could be used to control the overtones. Is there a name for this kind of synthesizer? Have I completely misunderstood it?

Link to comment
Share on other sites

7 answers to this question

Recommended Posts

  • 0

I believe the VERA PSG is meant to be an analogue to the SID on the C64. Nothing complicated, just some voices and simple waveforms. In fact, despite having more voices, the PSG lacks an ADSR envelope, which was a feature that the SID had. If you want more advanced features, you should try using the YM2151, an FM synthesizer chip also included in the Commander X16 (but not yet in the documentation).

Link to comment
Share on other sites

  • 0

Indeed admittedly I haven't heard VeraSound yet but my feeling is that it's a bit like the NES, but with lots of channels. You can do some synthy things with it, such as a chorus (heard often in Mega Man and Ninja Gaiden). And actually since the Vera has basic panning you could do a stereo chorus and some other crazy things I'd imagine. But if you're comparing it to the rich osillators of say a Dave Smith Prophet, well adjust your expectations a bit 🙂 No filters for one (so in this regard it is lacking from a true SID as well). And a feature I would like is multiple noise types (staticy noise and buzzy noise ala the NES) as that would be really useful for sound effects, but can also be fun musically.

Now that said, the fact we have 16 channels of chippy goodness is pretty neat! And though it has no hardware ADSR, the hope is for being able to use software envelopes perhaps. Some ideas have been tossed around the forums on how to do that. I'll admit it's not ideal but may be decently efficient for the CPU to manage (and actually I'm not sure if the envelopes you see in, say, FamiTracker for the NES are actually software vs hardware envelopes...).

Anyways I wouldn't discount it, but I would consider it more of a chiptune instrument than a juicy modern subtractive synthesizer. I think combining it with the FM sound is where things can get really interesting though!

 

Link to comment
Share on other sites

  • 0

Well the triangle waves don't have a lot of overtones. If N is the number of the overtone, the amplitude of overtones decays like 1/N for square and sawtooth, but like 1/N^2 for triangle (and triangle, like the equal duty square wave,has only odd harmonics). I.e. their amplitude decays much quicker. A triangle is a "good enough" approximation of a sine wave so that you can do some additive stuff with a bunch of 'em. 🙂

  • Like 1
Link to comment
Share on other sites

  • 0

Hmm good point, I hadn't though of that! On a modern synth, you'd typically mess about with FM by tying one oscillator to the other though as I recall? (I don't use triangles much on my hardware synths but perhaps I should)

Link to comment
Share on other sites

  • 0

VERA PSG is definitely not as powerful as SID. Like mentioned before, there are no hardware supported ADSR envelopes and no filters.

I wrote a music player with software envelope support that can be called from BASIC programs (and of course also from assembly or C) with some predefined envelopes and ability to test your own. I also wrote stripped down version with four simple sound effects for BASIC programs. I use standard VSYNC interrupt to update the envelope so it can only be adjusted 60 times per second. They both come with source code if you want to tinker with it.

Music Player:

https://www.8bitcoding.com/p/music-player-library-for-basic-programs.html

Sound Effects:

https://www.8bitcoding.com/p/simplest-sound-effects-library-for.html

  • Like 3
Link to comment
Share on other sites

  • 0

The PSG does lack some of the SID HW features, e.g. ADSR, Filters etc, but it can still pump out some great sounds.

Something like ADSR can be achieved in SW using timing and the volume control for the voice.

Take a look at the link below. It's a C64 Rob Hubbard routine with its SID values being translated (approx) to PSG values. 

 

 

  • Like 1
Link to comment
Share on other sites

Join the conversation

You can post now and register later. If you have an account, sign in now to post with your account.

Guest
Answer this question...

×   Pasted as rich text.   Paste as plain text instead

  Only 75 emoji are allowed.

×   Your link has been automatically embedded.   Display as a link instead

×   Your previous content has been restored.   Clear editor

×   You cannot paste images directly. Upload or insert images from URL.

 Share

×
×
  • Create New...

Important Information

Please review our Terms of Use