DSI Prophet 8

Discussions about anything analog, digital, MIDI, synth technology, techniques, theories and more.
hey_timj
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Post by hey_timj » Wed Jan 30, 2008 7:28 pm

in french there's only one worth to mean both 'annoying' and 'boring.' source of confusion.
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Post by Bitexion » Wed Jan 30, 2008 11:06 pm

Remember that hearing the oscillators even if your filter is 0 doesn't mean anything is wrong. Check if the filter is modulated by the envelope to "rest" at a higher sustain level than 0. Should do the trick :)

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Post by SWAN » Wed Jan 30, 2008 11:10 pm

...is the price in the US a flat $2000-or are there some deals to be found.....Im considering flying one in to the UK....;)

Anyone got any hot deals let me know...

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Post by Push-Pull » Thu Jan 31, 2008 4:07 pm

Remember that hearing the oscillators even if your filter is 0 doesn't mean anything is wrong. Check if the filter is modulated by the envelope to "rest" at a higher sustain level than 0.
Don't forget that the sound we hear thru the closed is filter is the sound of the oscillators not filtered !
Something like a bright Farfisa sound ! :D

A recording of this problematic sound.
Click on Image or Image

Still no answer from DSI...
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Carey M
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Post by Carey M » Thu Jan 31, 2008 7:10 pm

I'm pretty sure DSI will take care of the problem... unless it's something that is a result of the P'08 design, of course. How are you liking the Prophet otherwise, Push-Pull?

- CM

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Post by Push-Pull » Fri Feb 01, 2008 9:11 am

CM> It's a very expressive synth !! With plenty of modulations that follow the velocity and pressure, a patch can really take life ! 8)


And.... (snare roll !)
The answer from DSI:
I ran this past Dave and here is what he had to say...

There have been some customers asking about the internal circuitry of
the Prophet '08, specifically on the issue of oscillator leakage through
the filter when the filter cutoff is fully off. First, there are many
sources of filter control, so of course there will still be some signal
coming through if filter keyboard amount, filter envelopes, lfos,
pressure, wheels, or any other modulation is currently on. If ALL filter
controls are fully off, there will still be a little oscillator sound
coming through, but it is at a very low level, around 67 dB down from
full signal.

This is due to the analog ICs that we use in our instruments (the
Evolvers all do the same thing; interesting that no one mentioned that
in the last 5+ years of shipping thousands of units). Since the
oscillators and filters are on the same IC, there can be this small
amount of feedthrough. Of course, the fact that we use this Curtis IC
allows us to make an instrument with 8 full analog voices for
significantly less that what it costs for a single voice from other
companies!

Many vintage synths have the same properties. Some, like the Prophet 5,
do not have the same issue, but that's partly because the basic
signal-to-noise level is much lower than the Prophet '08. In other
words, the noise level on the P5 is actually 6 db higher than the
feedthrough level on the P8! If there is leakage at the same level, you
can't hear it since it's buried in noise.

Most players never notice the feedthrough, since it doesn't show up in
normal playing of normal programs. After all, the VCA is there to work
with the filter as necessary. When the VCA is off, the noise is 90 db
down on the P8, which is very quiet for a real analog synth.

In summary, yes there is a little oscillator feedthrough in the filter.
No, it can't be improved since it's internal to the analog ICs we use.
If you twist knobs a lot and find it interferes occasionally, try
tweaking the VCA controls at the same time.
In fact, all is here:
Since the oscillators and filters are on the same IC, there can be this small amount of feedthrough.
Ok, I understand well...
Last edited by Push-Pull on Sat Feb 02, 2008 7:30 pm, edited 1 time in total.
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Post by Pilot352 » Fri Feb 01, 2008 12:23 pm

I would like to point out something, too...

A "real" Hammond B3 is the most sought after and raved about keyboard, bar none. Every keyboardist I know either wants one, has one, or wants a keyboard that closely sounds like it. But, most companies who try to design to emulate it have to recreate it's bleed through, noise, and other kwerks or enthusiasts complain, "It just doesn't sound as good".

These "faults" actually give the keyboard it's character and separate it from the others.

Why do you think Dave put in the Oscillator Slop function. This is to emulate a flaw in analog design but when not there, the synth looses something.

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Push-Pull
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Post by Push-Pull » Sat Feb 02, 2008 7:17 pm

Hmmm... :roll:
Dave put in the Oscillator Slop function.
Cool.
(and wanted by the design team)
the "filter bleed"
Not cool.
(and not wanted by the designers...)

In fact, all I have to do is to mix the output of the P'08 with a some noise at -60dB and I have the sound of a P5 !! :D
The making of my modular... (ok it's in french, but the pictures are easy to understand !)

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Post by alan partridge » Thu Feb 07, 2008 10:40 pm

a bit more info on the oscillator slop?

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Post by Bitexion » Thu Feb 07, 2008 11:26 pm

I can only assume, since I don't own one. But the Alesis Ion has a parameter called Analog Drift. It makes sure the voices are never exactly the same pitch when you hit a key.

The voice allocation works like this: Each time you press a new key, the synth cycles to the next voiceboard. This is the main reason for the fatness of analog synths, because the oscillators on the voiceboards are not exactly in the same tune. With an 8-voice synth you had 8 voice boards lined up.

The analog slop will induce a slight difference in tuning from voice to voice on a digital oscillators that aren't capable of being out of tune. Not so much that you can hear it (unless you use the extremes of the parameter), only slightly so that you get the fatness in chords when all the voices work together. You can hear it slightly if you repeatedly stab the same key to let the synth cycle through all its voices.

The prophet-5 was the first synth to use this voice allocation system.

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Pilot352
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Post by Pilot352 » Fri Feb 08, 2008 12:44 am

alan partridge wrote:a bit more info on the oscillator slop?
From the Prophet '08 manual:

Osc Slop: 0…5 – The amount of random oscillator frequency slop. The analog oscillators in the Prophet '08 are very accurate, and will not drift. This works great for accurate sounds, and allows precise de-tuning. The Oscillator Slop parameter allows subtle amounts of frequency drift.

This is the DSI description. The P'08 uses DCO's which are VCO's that are digitally stabilized and controlled. This "slop" destabilizes the oscillators slightly to make them seem more "old school"
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Post by alan partridge » Sun Feb 10, 2008 3:04 pm

cheers, pilot ;.)

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Post by nadafarms » Wed Feb 13, 2008 2:21 am

So I finally played a Prophet 08 today at RobotSpeak in SF. (great place)

Always been a DCO basher... I was shocked at how much I enjoyed playing it and how much warmer to me it sounded than the poly evolver.

I guess I just want to take back some of my total DCO bashing, it actually had a lot better tone/character than I thought, even though its not VCO which I do prefer big time.

Just wanted to say wow, I'm totally rethinking it now!
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Post by alan partridge » Wed Feb 13, 2008 3:26 pm

cool, a lot of people say it doesn't sound "typically dco"...;.)

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Post by Synthaholic » Wed Feb 13, 2008 5:51 pm

I think there's more than one way to skin a... er, DCO. One way is to use a digital pitch source an an analog waveshaper. Another is to take a traditional analog VCO design and lock (sync) its pitch to a digital pitch source. And I'm sure there's other ways too.

Depending on the DCO's design, "slop" may be implemented in different ways, some of which may sound more VCOish than others.

I wonder what DCO design DSI used, and how they implement their "slop". If their DCOs are digitally-locked VCOs, and they implement slop by "loosening" the digital leash, it can be very VCO sounding. If they use a digital pitch source then they would have to implement "slop" digitally which won't be true analog drift.
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