Moog Music Forum

kvitekp wrote:Hi Amos,

Please shed some light on how external CVs are handled in Sub37 -- are they mixed into CV after the main CPU DAC, or they are ADC'ed first, and then added to a calculated value before it is sent to DAC. If the latter, what's the digitization frequency?

Thank you,
/Peter

Hi Peter,

It depends on the CV. The filter cutoff external CV is mixed into the final CV sum for the filter cutoff, after the CPU DAC. The pitch and volume CVs are scanned and added to the internal values pre-DAC. The raw inputs are scanned at something like 40kHz, although the sound engine values for external pitch and volume don't update that quickly (they are more like 4 kHz although this rate could be increased in the future).

Amos wrote:It depends on the CV. The filter cutoff external CV is mixed into the final CV sum for the filter cutoff, after the CPU DAC. The pitch and volume CVs are scanned and added to the internal values pre-DAC. The raw inputs are scanned at something like 40kHz, although the sound engine values for external pitch and volume don't update that quickly (they are more like 4 kHz although this rate could be increased in the future).

This is great, we can modulate filter at audio frequency, time to patch phone out into VCF CV

Am I correct to assume that internal modulation buses are currently updated at 4KHz too?

Thank you,
/Peter

i suspected you were from Moog...thanks Amos. Keep in mind that this whole thread was sparked by the comment in SOS about the Sub37 in the review.

so my question is, are you going to set Sound on Sound straight, and ask for a repeal in the next issue?

Cheers,
Blackout

What am I missing about the SoS article ?


R.

"The Sub 37 is an analogue/digital hybrid..."

for starters.

is it really? the Prophet 12 is an analogue/digital hybrid. is the Sub37 the same as the Prophet 12 then?

answer = no....

you can see how readers would get confused. i mean, i sure did

Hi Blackout

I think the problem here is simply if you read analogue/digital hybrid and think this automatically just means DCOs a là some DSI synths then you will believe that the description in SoS is incorrect.

Forgive me in advance if I am telling you what you already know. As with all forums you don't always know a lot about the background of other posters… unless they are Amos or DemonDan that is

My reading, and here I declare here a background of being both an Electronics Engineer and old enough to have built my own synth back in the 1970s, is that the 'Signal Path' of the Sub37 from Oscillator through VCF and VCA is entirely analogue in true Moog tradition BUT there is a lot going on digitally to support this.

Some of what follows might be guess work but….

Unless I am wrong the keyboard will be scanned digitally otherwise you could not derive paraphonic or polyphonic key presses from tapping off from a simple resistor divider tree like in the good old days . The keyboard position of the note or notes pressed are read by the processor which then outputs to note value, via a DAC, as an analogue CV to the VCO(s). This allows the processor to digitally add or subtract both an octave shift plus, if required, a small 'fine-tune' to keep the keyboard on track. Meantime the MIDI value(s) are also derived and output

The three curve glide options and legato/mono mode are likely to be digitally determined from one note to the next and output as a sliding CV to the VCO(s). You only used to get the exponential glide curve in t'old days due to the charge curve of the glide capacitor (I guess that is why that curve is still simulated).

As I read the SoS article and, I think Amos on Youtube, the Envelope/Contour Generators are also digitally derived before being converted to analogue CV for the VCAs.

The front panel is read digitally before conversion, where required, to analogue CV.

My reading of 'hybrid', for the Sub37 is … analogue where it matters supported by digital where it is needed


R.

In that case, Rufus, should we call th Little Phatty an hybrud too? My own interpretation is that an analogue synth has its signal flow all analogue, no matter what is digital around it: LFOs, MIDI, memory...

The point is digital/analogue hybridations can be of a zillion kinds... To me, that's mainly a matter of wording (and/or marketting), and quite subjective in the end of the day.

Damn, I had made the promise to myself I would never enter again a debate about wording

I am with you… I don't care how much digital 'support' there is…. if the signal flow is analogue then it is an analogue synth… and so are my Little Phatty, Sub Phatty and Minitaur too


R.

I'm inclined NOT to give Sound On Sound a hard time about this. For one thing, they gave an overall rave review of the Sub 37... and for another, I think it's really a matter of individual opinion/perspective, whether having digital envelopes & LFO would put a synth into the "hybrid" category.

The debatable part, in my mind, is whether the envelopes are in the "signal path" or not. I mean, they're not... they don't go through the filter or the VCA... they are control signals. But you still hear them... they induce audio as they move the VCA and filter quickly... and some golden-ears people are very sensitive to the way different envelopes affect the sound. Others aren't so sensitive to these subtleties.

So, I think SOS was saying that it's not as completely analog as some synths (the ones with fully analog LFOs and envelopes for instance) and hence a "hybrid" of analog and digital technologies... which, sure, it is. But it's also a purely analog synth, if you're talking about the classic signal path of VCO-VCF-VCA.

So Sound On Sound can call it a hybrid and you can call it an analogue synth and you're both right for your own reasons.
I think that's fine, it's not really spin or marketing at that point, it's a matter of different people's perspectives on what defines an instrument or a category, to them.

De gustibus non est disputandum, as they say

If you've gonna push a Digitally generated LFO into audio rate then it matters! (The Nyquist Theorem Peeps!) So if Moog puts a 1000hz LFO on a synth (and they did) and you can modulate the filter with this (and you can) then we should at lease know at what rate that LFO is being generated at, which damn well better be 2000hz at least (again Nyquist). Otherwise what is the point? Don't ask me, ask Dave Smith why he always puts a separate audio radio modulation on his filters?

Digital where is matters, Anaolog where is matters. Hybridity is good, just be wise about it.

Amos wrote:The debatable part, in my mind, is whether the envelopes are in the "signal path" or not. I mean, they're not... they don't go through the filter or the VCA... they are control signals. But you still hear them... they induce audio as they move the VCA and filter quickly... and some golden-ears people are very sensitive to the way different envelopes affect the sound. Others aren't so sensitive to these subtleties.

Thanks Amos!

There is so much discussion around comparing the Sub37 to everything that has come before, questioning if it is or is not made with the same pure, virtuous qualities of former, more glorious times. Be here now, my friends.

Amos, if I see you around town, I would gladly offer you a cold beverage to honor your good work.

furiousgreencloud wrote: we should at lease know at what rate that LFO is being generated at...

Sorry for the strong language Moog (Amos, Love You!) just did describe this, here. It's just i've being waiting along time for this information.

Now just open source the Slim/Little Phatty Fireware would ya!

kvitekp wrote: This is great, we can modulate filter at audio frequency, time to patch phone out into VCF CV

Am I correct to assume that internal modulation buses are currently updated at 4KHz too?

Again, it depends on what modulations we're talking about. For example, LFO generation and internal modulation of the filter and VCA happens at more like 13 kHz. The freely-assignable modulations update at around 4kHz. All of these numbers are subject to change (but only for the better) in the future.

honestly i'm really perplexed by how there could be so much confusion here.. you can click on any phatty, minitaur or whatever in the Moog line on their website, they all simply state "100% analogue signal path"...

and yeah, the SOS review was great, I already own a Sub 37 and somehow it made me love it even more just reading that.

if it's got presets, it's pretty safe to say there's gonna be some digital stuff happening in there, but again "100% analogue signal path".. otherwise there is always the Voyager Old School.

personally I don't think digital envelopes are "in the signal path".. but i can see how maybe that would be a point of contention... though i'm not sure I see why it would matter.

Thanks Amos for this great information. This is another reason why I love Moog. Amos takes his valuable time to explain things clearly with no marketing hype or BS. We all get the info we are looking for.

To me the Sub37 is analog. Of course there is going to be some digital control and I welcome it and it's for the better in my opinion. Just my two cents. The Sub37 rocks.