[sdiy] New DIY synth has born

[Thorsten Klose]

Hi,

On Monday 14 February 2005 00:35, Batz Goodfortune wrote:
> One thing I'm curious about however. How did you deal with the clock noise 
> that the OPL's are famous for? Or did you even find this a problem. Every 
> OPL3 based sound card I've ever messed with has this problem and I'd 
> wondered if that was a function of the sound card's topology or was a flaw 
> in the OPL?

I remember this problem, but unfortunately I don't have the possibility
anymore to compare the background noise of my MBHP_OPL3 module
with the noise of old sound cards (not that I cannibalized them all - I
just don't own a PC with ISA slot anymore)

I think it's an imperfection in the YMF262 and not in the YAC512 DAC like
somebody could assume, because the jittering noise can also be regognized
on the digital output stream

> I first noticed this on the venerable AWE32. If you shut down the FM input 
> to the EMU chip or so long as you never address the OPL3, you don't hear 
> that noise. Once you've addressed anything on the OPL3 and woken it up, 
> that noise just rings large. I've since investigated it on a lot of other 
> sound cards. 

here is a .wav file which demonstrates this noise:
-> http://70.84.40.25/midibox_fm/mbfm_background_noise.wav   (1.3 MB)

This sample is normalized (the 50 Hz buzz is caused by a big ground mess in
my studio ;-) --- once a single sound is played, the output volume will
never be damped completely by the EG, even if the release rate and the TLs
are set to a minimum. I've sweeped the multipliers at the end of the sample
("I'm still here") - the noise can be suppressed by setting the frequency 
multipliers to zero. This just reminds me that an automatic gate function 
could be useful :)

Best Regards, Thorsten.