Questions about the filter for the multi engine and the Lead Arp LFO

[JRock]

I've been making patches with the multi engine but I'm having a tough time getting filter definition.

I can hear it in the background but I don't feel like it's really latching on to the oscillators. It's fuzzy and noisy. Not at all like the filter for the bass and the lead engine. If I trun the resonance up or the cutoff too high I get squealing too. I've tried different Chips and it seems to be the same. It seems to work better if I turn the sustain down for the oscillator and use the ADR...

Almost the same thing happens when I route the filter to the LFO for the Lead engine Arp.

Is this common or am I doing something incorrectly? I thought maybe it was the 6581s but now I have it running 6582s and I'm having the same thing happen...

I'm pretty sure the board is built correctly and for the multi I have the filter routed to all the oscillators and as a single polyphonic instrument.

Also when I try to route the filter to the LFO for the Arp on the lead engine I get some squealing too. Is this just cause I'm pushing the filter too much? Both of these instances kinda sound like they might be related... Is it just an artifact of the SID ie: it happens to everyone, ooorrrrr Am I doing somehting wrong?

Also, I am just setting the envelope and everything for Ins 1 since I do not have any oscillators configured for individual voices. Should that make a difference?

Edited September 20, 2010 by JRock

[Wilba]

One thing that might be related to your issue... the 6581 and 8580/6582 have different filters (obviously), and also there's a difference in how the cutoff frequency registers work. TK has made allowances for this by making the filter range adjustable in the Ensemble.

ACh: selects the audio channel: L (Left), R (Right) or LR (both)

Min/Max: this is a global, patch independent minimum/maximum value which scales the Cutoff between the given range. It allows you to calibrate your SID (especially the 6582 and 8580) for a suitable operation range. In general 000/FFF (full range) is fine for a 6581, 000/600 are recommented for 6582 and 8580.

Log: this function applies a logarithmic curve over filter CutOff values which are sent to the SID. By doing so, it linearizes the CutOff of a 6582/8580. It should especially activated, if the keytracking function is used. It shouldn't be activated for 6581s.

The default for all Ensembles is related to whichever version of the firmware was present when the Ensemble "bankstick" was formatted... so if you switch SID types, the Ensemble might have filter settings which don't match the SID.

So check those settings and see if it makes a difference, if not, I'll try to help diagnose your problem some more.

[Wilba]

Also, I've never heard SIDs have any self-oscillating filter squeal unless I used feedback pots (audio out -> audio in, with filter "Ext In" param enabled). Are you using feedback pots? Are you using the typical filter capacitors (470pF for 6581, 22nF for 8580/6582)?

[JRock]

Thanks for getting back to me Wilba.

Well the 6581s are working great. I turned up the cutoff range (for the 6581s) to FFF and it's BZZOOOO BBWWEEEERRRRRNNNGGGG!! :thumbsup:

The 6582s are still not as dramatic as I think they should be (only for the multi engine). Especially after hearing what the 6581 are doing now. The envelope is working and the filter has some effect but I'm not hearing the resonance like I do with the lead and the Bass Engines....

It sounds more static then dynamic. Also I get a steady tone in the background if I put it on Bandpass?

I have the 22nf green rectangle caps in for the 6582s.

About the filter noise for the Lead LFO; I am not using feedback pots and I don't think it's self oscillation. It's more in the background, like it's part of the SID noise. All my SIDs are pretty noisy. But it kinda sounds like a tea kettle in time with the LFO :rolleyes: It's like a tone.

BTW I added the default assignments for the knobs to your wiki... I changed your text a hair where it said about being redundant. You may wanna check it out and make sure it's kosher. I'm not trying to step on your toes or anything :flowers:

[Wilba]

What version of MIDIbox SID are you using?

I vaguely recall there was an issue with Multi engine and control of the filter... but I got TK to fix it a long time ago. It was an issue with how the filter cutoff depth for a SID was the sum of the filter cutoff depth for each single osc "voice"... thus each voice played in isolation could only get up to 1/3 the maximum depth. I may be remembering it wrong... I'll have to dig through my old emails.

Perhaps this is related somehow... what's hard to determine is whether you are observing a difference in SIDs, a firmware bug or a hardware fault.

I'll have a play on my MB-6582 and see if I can get a difference between a single-osc Lead patch and a single-osc Multi patch.

[JRock]

I'm using V2 ORC37. I have 6582 2392 25 :)

Thanks

[JRock]

Duh!!! I had the filter cap placement wrong!

Apparently I thought it didn't make a difference since there were 6 holes. I've been fiddlin' with moving them in their sockets since I built it knowin' that it changed the way they sounded.... :rolleyes:

0

x

x

x

0

x

I apologize for leading you on a wild goose chase Wilba. Thanks so much for your Patience with me :thumbsup:

[Wilba]

ahh... good to hear you worked it out. If you're in the mood, try replacing 22nF caps with something bigger, up to 100nF, this will reduce the max cutoff frequency but it will be better resolution (less steppy) at the bottom end... i.e. good for bass patches.

[JRock]

Good to know! Thank you :thumbsup: