Shruthi-1 SMR4mkII Envelope/VCA Noise at Low Octaves

Hello all

I’m a longtime reader, first time poster here who just finished the shruthi-1 kit. I’m in the process of tuning the filter and noticed a bit of an anomaly. While playing the init patch with lower filter cutoff (~30) at A0-A1, I hear audible clicks that are tunable with the amp envelope release. With Att 0 Dec 0 Sus 127 Rel 0 (unit step), the envelope behavior is consistent with the VA synths I own, however, upon increasing Release (0-40ish) the clicking increases in amplitude and sounds slightly distorted. I’ve attached a 4 measure audio clip of the behavior I’m observing.

I’m going to quickly scan the presets to see if there are any in particular that one can play and reproduce the clicks.

Has anyone experienced anything similar with their unit?

Thank you for the help

Well, this is not a VA synth… welcome to the real world ;). Seems to be some bleeding in the lowest Octaves, Olivier will shurely explain in detail. The crucial question is are you annoyed by this or is it something that is rather theoretical and way out out of your daily use?

This was more of a theoretical case, after getting everything going I was trying many different settings to ensure that I had assembled everything correctly. The main reason for my post was checking if this behaivior is expected or due to an error in assembly on my part. I hadn’t soldered anything in about a year so I occasionally stayed on the pads a little longer than I would have liked.

Apart from this problem, does it sound good? :wink:

Your audio clip contains about 10s of pure digital silence.

I think it sounds really good, I’m going through right now recreating some of my previous patches and noticing how much less sterile everything sounds. I especially like the z waveforms so far

edit sorry about the audio file Oliver, I rendered the master track with another track soloed resulting in silence. I’ve attached the updated file.

Nothing unexpected here. If you want smoother envelopes, you can try increasing the value of C8 on the filter board (try 220nF or 470nF) - the risk is that the envelopes will sound less snappy.

Thank you for the quick reply Oliver, I may try changing the cap next time I open the Shruthi up. When I do I’ll go ahead and post up the results here as well.

Clicks with Envelope at zero is not a fault. This is a sign the envelopes are fast.

I have noticed a few people who tend to turn knobs either full off or full on, you can see it all over youtube even with some of the reviews from established magazines and shops.

Instead of changing the cap you could just increase the value of attack. If you change the cap then in a few weeks decide you must have a clicky sound for a percussive patch you wont be able to do it.

Having said all that this is a DIY synth and it would be interesting to know what your mod does, everyone is different so perhaps you can create the perfect envelopes for your ears.

Heres an copy from the Waldorf FAQ on this topic:

Q: Why do some synths produce clicks?

A: Chapter 1: The click in theory

A click is produced when a very fast level change in the audio signal
occurs. You can easily check that on your home stereo when you play
back a CD and switch the Source Selector back and forth between CD
and a source that doesn’t play anything.

The brightness of the click depends on the speed of the level change.
The faster the level changes, the brighter is the click. So, the
level change speed can be compared with the cutoff of a lowpass
filter. There is an easy formula for it:

Let’s consider a level change from full to zero (or from zero to
full) output from one sample to another on a machine that uses
44.1kHz sample rate. So, we first transfer the sample to milli

1 sample equals 1/44100 second, which is = 0.02267573696ms.

To calculate the cutoff frequency of the click, just use this formula:

Cutoff (Hz) = 1000 / Level Change Time (ms)

which in the example results in:

44100Hz = 1000 / 0.02267573696ms

Whoops? This the sampling frequency and, err, very bright.

Chapter 2: The click in the real world

Now, how could this knowledge help you and what has it to do with
Waldorf synthesizers? Easy:

When you play a sine wave sound, only the base frequency (the
fundamental or the 1st harmonic) is present. That means, when you
play note A=110Hz, no other frequencies are involved except this
110Hz oscillation.

Now, what happens when you abruptly cut the sine wave to zero when it
just is at its maximum level? You get the same effect as with your
home stereo.
From one sample to the next, the waveform is brought from maximum to
zero, resulting in the forementioned bright click.

The same applies when the opposite happens. On Waldorf synthesizers,
you can setup the oscillators so that their phases start randomly
when a new note is played. So, you never know at which level the sine
wave is when you hit a note.
Consider it would be at the maximum level, you would get an immediate
change from zero to maximum when the amp envelope’s attack rate is
set to 0.

BTW: the effect is the same, when you have a bright waveform but
filter it so that it is very hollow.

Chapter 3: In which situations does the click occur on my Waldorf synth?

There are several situations when you can get a click and when you
know where they happen, you can try to prevent them:

  • Amp Envelope Attack. On digital Waldorf synthesizers like the MWII
    and the Q, the Attack rate can be as short as 1 sample. This means
    that the amp volume of a note can change from zero to maximum in one
    sample, or in ms: 0.02267573696ms. This results in a very bright
    On the Pulse, we chose a minimum attack rate of 1.9ms, resulting in a
    click with a maximum cutoff of around 526Hz. When you own a Pulse,
    you probably know of the 1.9ms number from the user’s manual, because
    that’s the update speed of all CVs that are used in it.
    So, when you hear a click on note start every now and then, just
    increase the Amp Envelope Attack rate until you don’t hear a click
  • Amp Envelope Release. Here, the same as with the Attack rate applies.
    When you hear a click when you release a note, increase the Amp
    Envelope’s Release rate.
    If the click still persists, you should also check the Release rate
    of the Filter Envelope. Maybe the filter closes very fast, which can
    result in a click, too.
  • Voice Stealing. We know that this is the most annoying situation.
    But, the click helps you: When you hear a click at a certain position
    in your song, you know that a voice stealing happened and you can
    easily shorten or delete notes in the editors of your sequencer.
    When you count the notes and say that they don’t exceed the maximum
    number of voices of your synthesizer, just keep in mind that other
    notes might still be in their release phases and therefore have to be
    added, too.
  • Mono mode. In Mono mode, a click might occur when any envelopes
    (Amp or maybe Filter, too) are set to retrigger on new notes. When
    the Attack rate of a sound is greater than 0, they are brought to
    zero so that they can go up to their full level again. This rapid
    change to zero results in a click.
  • Unisono sounds. Here, a click might occur even heavier. Unisono
    sounds easily exceed the maximum number of voices and because they
    steal not only one but several notes at once, a click can be a
    lot more present. It is louder and happens more often. You should
    check several points on unisono sounds to lower clicks as much as
    possible: are the envelope rates set to reasonable values, are the
    oscillator phases set to free, is filter keytrack set to 0% (because
    this can also be a rapid change) and so on.

Chapter 4: Why does my synth xy (insert product name here) produce no clicks

Should I really answer that? Because it is slooooow.
Some japanese manufacturers (I don’t say names here) prevent voice
stealing clicks by fading out voices slowly before they start new
notes. Hey, brillant idea, why doesn’t Waldorf do that? Because it
ends up in a very bad MIDI timing (and those japanese synths are
well-known for that).
Furthermore, most of these synths are sample-based, which means that
their attack behaviour is stored in the sample that they should play.
So, a click on note start is also not possible because the sample
somehow gradually fades from zero to maximum.
If those synths allow you to change the sample start position, they
hopefully produce clicks, too (if not, they also have slow envelopes
which we don’t hope).

A couple of days ago, someone mentioned the Matrix 12 producing no
clicks on retriggering envelopes. Yes, that’s correct, because the
Matrix 12’s minimum attack rate is around 20ms. Or in other words:
its envelopes are among the slowest you can find in a synthesizer.
The same applies to all synthesizers of the Matrix series, because
they all used Curtis chips that had an automatic smoothing filter to
prevent steppiness. The older Oberheim synths like the 4-Voice were
better here.
Also, the Waldorf Microwave and the Waldorf Wave used those Curtis
chips, but when the Attack rates of the envelopes were set to 0, this
smoothing filter was temporarily switched off, resulting in an abrupt
change. Attack 1 there is the same as minimum attack on a Matrix

Chapter 5: Conclusion

You know that we at Waldorf could prevent clicks by increasing the
minimum envelope rates or allowing bad MIDI timing. We could also
prevent that the filter resonance can destroy your hearing ability or
that you could play a C major chord. But who are we that we could
decide what you want from a synthesizer. Clicks can even be
musically useful and add a kind of randomness to a song that brings
it to live. A very good example is the bad, ugly, annoying, but
famous and beloved keyclick on Hammond organs.
Recently I bought the latest Art Of Noise album “the seduction of
Claude Debussy” produced by Trevor Horn and played by the creme de la
creme (even including Lol Creme of 10CC and Godley&Creme) of
musicians and I heard a lot of clicks during a couple of tracks. I am
even quite sure that they came from Waldorf synths but I don’t know
if. You can easily imagine that I had a smile on my face.

I hope you now have even more fun with your “clicking” Waldorf synth. ^

I think the Waldorf view is similar to the BMW view, you can drive at 150mph but we suggest you only press the pedal half way…

Its more “Be aware your Car drives 150MpH if you push the Pedal to the bottom.”

Yes that’s it :slight_smile:

I think they applied that prevent-voice-stealing-clicks-technique to my japanese car. It’s always a lot slower than other cars when the light turns green (and no problem with my reflexes).

Get an Italian one :wink:

In search to reduce the VCA clicks and the PWM bleeding which I can hear with small VCA release values I came up with this mod in the gain current source circuit.

This mod reduces the VCA clicks a lot and the PWM bleeding is almost removed completely.
This without the VCA becoming to slow.

The scope picture is the current output from Q1
Purple is the normal circuit with 100nF cap
Yellow is the circuit with a 220nF cap mentioned above
Green is the modded circuit where R8 is replaced by a small sub circuit
The first part is the PWM with 50% duty then 1% duty then 99% duty then back to 1% duty again

You can see that the PWM bleeding at 50% duty is almost gone and the circuit response time is better then the 220nF option.

Regs DMM

Fascinating stuff DMM, and by splitting the lowpass filtering across two stages to double its slope (12dB/octave instead of 6) that looks like a great reduction of the 39kHz component!

However, assuming you matched the envelope settings for each of the three traces, I notice the envelope for no.3 is still slower than no.1

Have you tried your pre-filtering option, but with smaller caps than 100nf in both positions (by the look of the relative timings, perhaps 68nF), so that overall VCA timings can be as fast as the original circuit, but still with better 39kHz filtering?

Also, you can of course you the same extra filtering (with R21) for Filter resonance.


@ yewtreemagic
Yes all three traces have the same traces. I didn’t try it for the reso current source yet but this already is a big difference and very easy to do. At 50% duty the 39kHz component is the largest and you can see in the scope picture it’s almost gone.

I’ll test your suggestion with the 63nF caps to see the result.

@ yewtreemagic
New scope picture with your values.
Purple is the normal circuit
Yellow is mod circuit with 2x 100nF caps
Green is mod circuit with 2x 63nF caps

With the 63nF caps the response is the same as the original circuit! Nice ;-))

this is a scope view with the 39kHz component enlarged @50% duty
Again purple is the normal circuit
Yellow is mod circuit with 2x 100nF caps
Green is mod circuit with 2x 63nF caps