Fro the unofficial Waldorf User FAQs:
faq.waldorfian.info
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
seconds:
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
click.
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
anymore.
* 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
synthesizer.
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.
.