The Official Sequential/Oberheim Forum
SEQUENTIAL/DSI => Prophet => Prophet Rev2 => Topic started by: skipgilles on March 28, 2020, 02:58:22 PM
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I notice a rather loud sputter or plop at the onset of notes when unison is on. It does not happen at each triggered note, but rather randomly. I made two short recordings to illustrate:
This wav (http://www.gillesdutilh.com/parking/sputter_rev2/sputter_bass_comparison.wav) contains one note with, and one note without the sputter at the start. The frequency spectra of both are attached below.
This second wav (http://http://www.gillesdutilh.com/parking/sputter_rev2/sputter_bassline.wav) shows how this sputtering becomes rather obvious when playing a quicker baseline.
I believe it does not only occur at low notes, but you hear it best at lower notes, since the sputter has a high frequency. The current patch has no velocity-response, both notes are triggered equally.
Is this normal behavior?
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I had already noticed this and mentioned it somewhere else on this forum. But nobody seemed to understand or even notice it.
I believe it's caused by the oscillators being all restarted in sync with each other randomly (more noticeable when playing successive notes far apart on the keyboard), creating a louder than usual output because of all the waveforms adding up together? And it's even more noticeable with the parameter Unison Detune set to anything else than 0.
The oscillators in the REV2 are definitely NOT free running all of the time, like on a VCO synth.
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Hmm, so you suppose it's just a limitation. It is actually pretty loud. Do you know of any workaround?
By the way, I see my second link to the wave is incorrect, it should be this wave (https://www.gillesdutilh.com/parking/sputter_rev2/sputter_bassline.wav).
(can I not edit my previous post?)
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I remember this issue being brought up before, as I had experienced it myself, but unfortunately I don't remember if there were any definitive conclusions made on the topic then. I don't remember a solution. Like Alain said, the onset phase of the osc's seems like a highly probable cause. But if I'm not mistaken, I think the amp envelope(s) was also being discussed as a possible reason for this behaviour, ie the "jump" from wherever (what level) each voice env is at, to wherever the starting point of the env is when a voice is retriggered. If my memory is right, I think I've had this issue even when not even using unison, just a lot less noticable then, as even with chords the notes are rarely triggered at the exact same time.
Wish I had more information and less speculation on the topic.
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I agree wholeheartedly with you Maxter.
But in this time of global shutdown, we'll probably never get to the bottom of this. Certainly not from Sequential anyway...
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I agree wholeheartedly with you Maxter.
But in this time of global shutdown, we'll probably never get to the bottom of this. Certainly not from Sequential anyway...
Well, I finally had time to make these recordings and start the thread thanks to the virus-crisis :)
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This reminds me of an excellent Supertramp album called: Crisis? What crisis? ;-)
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For those having no clue what I'm talking about, select built-in patch F24 (intellectual lead) and press sequencer play. The sputtering is all around. Or is it not? Then there is something wrong only with my machine.
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On F1 P24 with the sequencer running, I wonder if the issue is being caused by the filter envelope being too long for the speed of the sequence? Basically the filter envelope doesn’t have the time to finish before the next note sounds. I ‘shortened’ the filter envelope and I think the noise went away.
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True, if you know in advance that you will play only quick sequences, shortening the envelope might solve this. In my situation, where I aim to play bass, which is sometimes slow, sometimes quick, this is no solution.
I actually do consider this a real limitation of the instrument. I am forced to use a non-unison bass patch, since sound technicians at live venues complain about the sputter (rightfully!). This limitation to using a single-oscillator forces me to play with a lower output level (I adjust all non-bass patches to the low output level of my default bass patch), with all obvious negative effects for sound quality and new complaints by sound technicians!
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I'm not trying to say there isn't a problem, just offering possible workarounds :)
Personally (yes I know this might not apply to others :) ) if I'm playing a fast bass line then I don't want a long release so I'd probably save a bass patch as 2 different ones, one for fast play and one for slower play which could have a longer release etc.
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This seems to me to simply be the way an Amp ADSR and Filter ADSR interact. I don’t know what solution they could possibly implement unless you expect an on board limiter..
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I remember the discussion and now totally hear and see the issue.
I did some investigation and found I can reproduce the issue with a unison 1 note, VCO1 triangle and simply alternate 2 notes at the octave, keeping the upper one pressed. The issue disappears with a fair amount of glide (more than 60).
I recorded the sound and saw some very ugly transitory.
I tested the exact same on the Subsequent and the signal is just continuous and no artifact is audible; looks like the subsequent is waiting for the end of a cycle before it commutes the frequency while the REV2 changes it as soon as you press a key hence producing discontinuity.
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Posting on this thread as it mentions F1 P24....
I’ve noticed just now that on this patch the octave from middle C seems to play differently to all the other keys. They seem quieter for want of a better description. Does anyone else notice this?