my first SID is making notes, but sometimes not when i want it to

[tarzan boy]

Hello,

yesterday i got my first set of control surface done, the step A (5 menu buttons and encoder for LCD) and my whole thing is up and running. I'm super psyched.

I have one problem though: If i go "too crazy" with the settings i do on the sid (more than a few mod matrix settings on, use the 'delay' feature -the one next to attack in the osc menu, change envelope or LFO or LBH pass filters quickly) then I get this high pitch whine that I hear whenever a note is not being played.

I was messing around with the LBH filters while this whine was on last night and they affect the sound.

Is this problem something in the SID chip?

I read a thread from a  year ago with this problem

http://www.midibox.org/forum/index.php?topic=1689.15

but it was mentioned at the end of long thread with no follow-up. Anyone?

thanks

[TK.]

There are a lot of threads about this SID typical issue, it's really a FAQ!

At least you can read something about this in the interview with Bob Yannes:

http://stud4.tuwien.ac.at/~e9426444/yannes.html

The issue wasn't budget, it was development time and chip size constraints. The design/prototype/debug/production schedule of the SID chip, VIC II chip and Commodore 64 were incredibly tight (some would say impossibly tight)--we did things faster than Commodore had ever done before and were never able to repeat after! If I had had more time, I would have developed a proper MOS op-amp which would have eliminated the signal leakage which occurred when the volume of the voice was supposed to be zero. This lead to poor signal-to-noise ratio, although it could be dealt with by stopping the oscillator. It would also have greatly improved the filter, particularly in achieving high resonance. I originally planned to have an exponential look-up table to provide a direct translation for the equal-tempered scale, but it took up too much silicon and it was easy enough to do in software anyway.

There are some 6581 with less noise, but it's hard to identify them - you have to try it out.

The issue doesn't exist on the 8580

Best Regards, Thorsten.

[tarzan boy]

Well I am aware of this problem, yes, i have indeed read about that. and noticed it inside the C64 when using Prophet64...

and i don't really consider it a problem because the 'ghost note' is just as loud as the noise floor anyway.

What i'm talking about is a LOUD, SHRILL high pitch steady note that is on when a note is not being played. This note does not correspond to the note played previous, whether i do a C-0 or a F-4, its still the same high pitch squeal.

[TK.]

Very strange, could you please post a mp3 sample?

Best Regards, Thorsten.

[Niijaooh]

Mine does this to, but only when using the Delay function in the OSC envelope. When raising the value it makes same noise and then it gives out this hi pitched scrill and I can only stop it by changing patch or reset.

[pwx]

I had a similar prob when I made my first MBSID.... I don´t really know what it was, but after triple-check my soldering(Ground!!!!) and after putting  heatsinks at the 7805 and 7812... the problem was gone and never came back ::) :P

sorry, no better idea at the moment

pwx

[Niijaooh]

Try the bended engine SID 1.7 303 engine http://www.ucapps.de/mios/midibox_sid_v1_7_303beta9.zip

It solved my Delay-feedback-shrill problem (but I still have a portamento bug)

[tarzan boy]

can the 303 engine coexist with the normal one? i dont know too much about the 303 one, i was hoping to get all my normal midibox sid stuff straight before i delved into that.

Yeah, it does sound like you had the exact same issue as me.

to all though: sorry i havent uploaded a sample of the problem, I've been picking pears for the past 2 weeks (only one week left YESS!) on a farm so when i get home i'm so exhausted that i just look at the soldering iron, the half completed bankstick board, and my dissasembled core/sid/din/lcd and sigh..

but this weekend i hope to get back on that train again. or if it rains this week....