SV: Re: [sdiy] Roland DCOs

karl dalen dalenkarl at yahoo.se
Wed Feb 27 16:39:17 CET 2008


--- Dave Manley <dlmanley at sonic.net> skrev:

> There are still a few 
> mysteries - I never got around to figuring out what that PA381 dual VCA 
> is doing, or what the mystery chip is next to the DAC.

Most likely a buffer for the DAC since they often are not capable
to deliver the current to the storage caps.The PA381 may be used as
final volume setting + velocy.

> I was also 
> surprised by the ceramic chip caps used in the filter, after hearing 
> discussion about the suitability of different cap materials for audio 
> use (makes me wonder if the Moog LP uses chip caps in their filter).

Its peculiar indeed, i have studied the Andromeda and it seams to
use ceramic caps as well.

> There was also the unresolved issue about what exactly the "oscillator 
> slop" parameter does.  Regarding the code, you could always get a hold 
> of one and plug into that RJ-45 debug port ;-)

Does the DSPIC have memory protection or tampering blocking function?

KD
> 
> -Dave
> 
> Eric Brombaugh wrote:
> > Thanks for posting that. I note that I also got the SPI DAC details 
> > wrong - it's not an 8-chl SPI DAC, but a single channel SPI DAC with a 
> > 24-chl analog demux & S/H configuration.
> >
> > Don't know about you, but I think that's a fairly elegant use of 
> > resources. I bet the code for the voice processors is something to 
> > behold...
> >
> > Eric
> >
> > On Feb 26, 2008, at 11:42 PM, Dave Manley wrote:
> >
> >> Here's a labled pic of the voice ckt I posted to AH at the time:
> >>
> >> http://www.sonic.net/~dlmanley/p08VoiceLabeled.jpg
> >>
> >> Unfortunately, the pics (I believe taken by Stephen Johnson) were a 
> >> bit blurry and made it impossible to dig all the details out, but 
> >> what Eric describes is essentially correct (except there's one dsPIC 
> >> per two voices).  Looking at the pics again, the clock osc labeling 
> >> is not clear enough to make out, but looks like 4?00, so perhaps it 
> >> is 40MHz.
> >>
> >> -Dave
> >>
> >>
> >>
> >> Eric Brombaugh wrote:
> >>>
> >>> I seem to recall a similar discussion on AH back when the first 
> >>> internal photos of the DSI P08 came out a few months ago. From what 
> >>> I recall of that thread, the P08 uses a bunch of the motor control 
> >>> dsPIC chips. There's one dsPIC per voice controlling a CM3396-like 
> >>> chip. The motor control variety has a bunch of nice PWM outputs that 
> >>> can presumably provide the digital divider output, plus there's an 
> >>> 8-channel SPI DAC being used for the numerous voltage control points 
> >>> on the '3396. To top it all off there's another dsPIC that talks to 
> >>> the keyboard, panel controls & MIDI, coordinating the behavior of 
> >>> the per-voice dsPICs.
> >>>
> >>> At the time, I sat down and figured out the frequency resolution 
> >>> you'd get from the dsPIC dividers and it looked pretty decent. 
> >>> Here's what I wrote then:
> >>>
> >>> -----------------
> >>> I was curious about which dsPIC was being used. Notice that it's the 
> >>> 'MC' version - that probably means that he's using the motor control 
> >>> PWM channels to generate the waveshaper drive pulses.
> >>>
> >>> The motor control time base has 15-bit resolution with a 1/4/16/64x 
> >>> prescaler - that should give plenty of frequency accuracy. I've no 
> >>> idea what the dsPIC clock rate is, but assuming it's running near 
> >>> it's maximum, 40MHz is a good ballpark. Given that, you get the 
> >>> following resolution at the various prescaler settings:
> >>>
> >>> 1:1 - Range is 2441Hz and up. Resolution is ~0.15Hz at 2441, ~2.3Hz 
> >>> @ 10kHz.
> >>> 1:4 - Bottom of range is 610Hz. Resolution there is 0.03Hz, 0.6Hz at 
> >>> 2.4kHz.
> >>> 1:16 - Bottom of range is 152Hz. Resolution is 0.009Hz, 0.15Hz at 600Hz
> >>> 1:64 - Bottom of range is 38Hz. Resolution is 0.002Hz, 0.04Hz at 150Hz
> >>>
> >>> Those resolutions give about 1/10 cent accuracy at the low ends of 
> >>> the range and 1/2 cent at 4x higher. Not too bad.
> >>>
> >>> Not sure what the overall frequency range of the '08 is, but if it 
> >>> goes lower than 38Hz then the dsPIC is may be running slower than 
> >>> 40MHz.
> 
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