[sdiy] Odp: Pink?

Mattias Rickardsson mr at analogue.org
Tue Aug 21 12:01:48 CEST 2018

Thanks for bouncing around thoughts about this topic, taking it in
interesting directions. :-) Bouncing back some comments below:

On Fri, 17 Aug 2018 at 16:45, Quincas Moreira <quincas at gmail.com> wrote:

> The waveforms are what they are, squares and saws simply sound bright due
> to the nature of the waveforms and their harmonic content. Which is why
> since the early days filters have been used in synthesis, or waves like
> triangle and sine with variable waveshaping to achieve the desired amount
> of higher harmonics. The model 15 for example has a nice non resonant
> filter bank precisely for these kinds of adjustments. I just use the 3 band
> eq in my Hexmix mixer to roll off some highs when needed. To do so in the
> VCO itself would IMO be undesirable, you may need those high harmonics to
> make a filter sweep really sing, or for FMing other sound aources etc.::
> My take on this is: Just use eq to taste when needed.

True, it's "just" an EQ adjustment - but my point here is that it's the VCO
waveform in itself that is too bright, not that the resulting synth sound
is too bright in the end. What I mean is that the VCO gets too bright and
also too loud when opening up the filter, compared to when the filter is
almost closed and everything sounds alright. If this would be compensated
with an EQ, you'd have to adjust that EQ when tweaking the filter. And
since the filter is typically tweaked by its envelope every time a synth
sound is played, the EQ would have to follow the filter envelope. All this
just to compensate for a problem with the VCO signal. Not really efficient!

I don't fully agree with that history writing regarding the use of filters
in synthesis, but that's less important here. :-)

BTW, I should also mention that I'm not suggesting that the spectral
balance of VCOs is necessary problematic in modulation routings, only in
the audio routing that is routed in the direction of human ears.

On Fri, 17 Aug 2018 at 17:18, <mskala at ansuz.sooke.bc.ca> wrote:

> But any low-pass VCF with at least one pole will roll off the high end at
> at least 6dB/octave in the limit of high frequencies, which is already a
> sharper roll-off than traditional 3dB/octave pink noise.  So if the output
> of the VCF still sounds too bright for you (too much high-frequency
> content) and you want a sharper roll-off, I'm not sure what to tell you
> except to try a sharper filter.  And if you don't like the sound of a lot
> of resonance, try using less resonance.

Full resonance often sounds OK in the low end of the cutoff range, but too
loud in the highs. Having the same amplitude regardless of the cutoff
frequency, a whistling resonant filter even has more excess energy in the
highs than the already too bright VCO waveshapes have. :-)

Using less resonance overall would decrease it also in the lower end.
Introducing a cutoff-dependent resonance amount (reducing the resonance at
higher cutoffs) is actually quite useful (and has been used successfully to
alter the perceived character of a filter), but also has a dilemma in the
few cases where a whistling oscillator-like sinewave *is* the expected goal.

On Sat, 18 Aug 2018 at 09:24, Roman <modular at go2.pl> wrote:

> You can always limit the slew rate, that will give you more pink, or even
> red or brown.

This first appeared to me as a less good suggestion, something that often
happens with the radically best of ideas. But:

> For example I enjoy very much a square-ish waveform that is derived from
> triangle fed to overdriven amplifier. It produces almost a square wave when
> you look at it at the scope, but it's more like trapezoid. And the slope
> changes with frequency so it sounds nice, like filtered.
> Sawtooth may be not so easy - I can imagine a VCO with 2 integrators...

This reminds me of a very minimalistic triangle core VCO that has a mode
where it is (mis)used as a sawtooth oscillator by letting one of the
triangle slopes have a much higher rate. The resulting "sawtooth" wave is
far from perfect, having a much slower reset than normal, but still quick
enough to give all the audible overtones in almost the right amount. But to
my great surprise there was a different tone to it that people actually
liked more than ordinary oscillators.

Designing such a slewed sawtooth VCO in a more thorough fashion might be
somewhat of a heavy exercise. I'd want the slewrate to be a controllable
parameter; I'd want it to follow exponential and linear control - something
that would need to work regardless of the slewrate used; I'd want the
timing of other generated waveforms to follow the zero crossings and not
the peaks of the sawtooth; and finally, for FM duties and freedom of thumps
I'd want the saw to be DC-free, meaning that the start and end of the
slewed reset slope would need to be equally far from zero - which wouldn't
be the case of an ordinary sawtooth with a slew function hung onto its

The overdriven triangle wave is actually a great parallel example to this,
thanks for mentioning it!

On Sat, 18 Aug 2018 at 11:12, Rutger Vlek <rutgervlek at gmail.com> wrote:

> I share your opinion, when it comes to solo sounds from analog
> oscillators. I've often noticed how these sounds are EQ'd and otherwise
> processed (e.g. Lots of reverb) at mixing stage such that the resulting
> master actually follows a rather pink (3 dB/oct) frequency spectrum.

Yes, and it would be nice to get a more "production ready" sound out of
synths to begin with.

There's a really accurate static pink filter implementation on the Esp
> (Elliot) website, but I prefer more control so I designed a spectral
> tilting module for Eurorack. It allows you to tilt the spectrum (even CV
> controlled!) of a sound up to a positive and negative 3dB/oct slope. I've
> achieved great results with it on my VCO's, being able to make them
> gradually more pink. Combining a pink-ish VCO voicing with overdrive also
> sounds wonderful, and avoids harshness. Putting tilting under CV control is
> also cool, as it gives a very gentle and natural modulation of timbre (e.g.
> modulation with lfo or brightening with higher velocity). I've even
> achieved a very passable analog leslie simulator with it in a stereo
> configuration, partially because my implementation of tilting also involves
> small phase shifts that are modulated along with timbre.

I've studied that tilting module of yours before, and was struck by how
much more useful it was compared to my initial reactions. Good ideas!

On Sat, 18 Aug 2018 at 19:16, KD KD <pic24hj at gmail.com> wrote:

> Some of the Roland polys have a overall "designed" gain and spectral curve
> JP6/MKS80 i vaguely recall. Its the only poly synths i have seen doing
> this but
> i can imagine stoneage stuff like PolyMogg, ArpQuddra, Bork Triddent might
> have some of this implemented due to crap PA's back in those days, but
> none
> of above mentioned for the sake of pinkyfy "certain" function modules as
> such.

Are you referring to the slight bass boost that is introduced if the HPF
slider is set to zero? I think this is quite an ingenious trick, not only
to make the sounds more impressive but also to actually introduce some kind
of EQ that balances up the sound in a similar fashion to our discussions

On the other hand the brightness you experience might be a physical
> condition you have deteriorated into? you no longer a youth, i for instance
> entered glass-eye condition some years ago and 0603 is like flys fart to
> solder! :-)

"Glass eye" is a... let's say... INTERESTING way of translating that word
to English. People will be quite impressed that you're still into building
stuff. ;-)

On Mon, 20 Aug 2018 at 12:57, Roman Sowa <modular at go2.pl> wrote:

> After breakfast I usually come up to conclusion that morning's idea was
> over complicated and can be done much simpler.
> It wasn't different this time either :)

Most brilliant ideas are made mainly out of breakfast. Breakfast is one of
the most important basic elements, after carbon, oxygen and sillycon. :-)

Actually, considering my wish to correct the spectral balance of both VCOs
and VCFs, a Roland-inspired (but extended into also attenuating the highs)
post-EQ might be the best (or at least simplest) choice after all - for
pure synth sounds. Its only big drawback would be that the sound of the
filter is EQed, giving it an even sharper slope. Wouldn't be much of a
problem I guess.

If a VCF is used to process samples or other "correct" sounds that
shouldn't be EQed further, the story is different.


> On Aug 17, 2018, at 09:09, Mattias Rickardsson <mr at analogue.org> wrote:
> I often experience VCOs "too bright", having too much high end in the
sawtooth & pulse waves.
> I often experience VCF resonance peaks "too bright", being too strong at
higher cutoffs.
> I often experience white noise "too bright", having too much high end...
> ...while pink noise feels more balanced. Equal power per octave, not per
> Also, good sounding loudspeakers/studios tend to have a bit pink-ish
spectrum roll-off from the sound source to the listener position,
suggesting that some sort of pinkification of clean sounds could be
> So, why aren't VCOs and VCFs more spectrally pink?
> Have there been any attempts historically to alter their characteristics
a bit in synths? :-)
> /mr
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