Tides (v2) PLL syncing with external acoustic instrument

Hello all, first-time poster here!

I recently picked up a Tides (v2) from my local synth shop, and am interested in using the integrated phase-locked loop on the clock input to sync the pitch of Tides to an external acoustic instrument for its ability to generate harmonics/subharmonics of the frequency. In this case, I am using a saxophone with my system.

I am using a contact microphone to avoid any extraneous sounds being picked up beside the pitch of the saxophone, and am running it into my eurorack system using Ears to boost the signal up to modular level and get an envelope from it.

When it tracks well, it tracks superbly well, but when it doesn’t it seriously doesn’t. This mostly happens in the low register of the instrument. Tracking analog oscillators of any shape at any pitch I can throw into the clock input is no problem at all for Tides, so I suspect that I need to find a way to clean up or modify the signal of the contact mic somehow before it hits Tides to allow it track it more effectively.

Anyone have any ideas I might try to get this up and running? The octave and a half or so of the instrument where this works leads to some incredible sounds, and I’m determined to extend the awesomeness across the whole range!

Tides’ clock input is… a clock input: it is digital and only records the high/low state of the signal. It does not “see” the full waveform of the signal, and decent pitch detection algorithm couldn’t even be implemented on such a coarse measurement of the signal. The clock recovery algorithm measures the time elapsed between rising edges – no more, no less. It has not been designed to track arbitrary audio signals, just basic waveforms.

I suspect that your issue is that the waveform is not monotonic: it has several “wiggles” or “kinks” per period. You can try one of the following (or even both):

  • Process it with a steep low-pass filter to remove all harmonics and make the waveform look as close as possible to a sine wave (obviously, the challenge is that the low-pass filter, if it is very steep, should ideally track the pitch of the fundamental).
  • Crank the gain to the maximum to turn it into a square wave (this works only if the wiggles do not cross zero).
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Thank you for your fast and detailed response!

Just did a few experiments with the scope, and it seems that it tracks the best when I use the maximum amount of overdrive I can throw at the signal. That said, I’ve barely started out with eurorack so my options are currently limited.

Here are some scope images that might help:

1: Signal from the contact mic unaltered besides the gain from Ears:


2: Signal with the maximum amount of gain I can give it with my current assortment of modules (Ears at max gain heading into Clouds Parasite on max gain with dry/wet fully ccw):

3: Signal with the maximum amount of gain, then low pass filtered with an Intellijel uVCF to make it as smooth as possible:

All three of these tests were performed on the same note of the saxophone, at as close to the same volume as I can replicate. After testing these out on Tides, I think the solution overall is probably as much gain as I can possibly throw at the signal to make it close to a square wave. The lowpass version simply didn’t cross the threshold for Tides to detect a gate and sync, likely due to a lack of gain as well.

In the upper register of the instrument it works phenominally well, pure and clean tone where you can’t tell the difference between it syncing to an analog oscillator or the saxophone. When a lot of drive is thrown on the signal in the low regsiter, it hits the right pitches (massive improvement from my earlier tests) but the timbre is more of an aggressive hard sync like sound instead of Tides unaltered tone.

I think I might also try using a comparator to force the signal to become a hard on/off to more align it with the kind of thing Tides is expecting at the clock input. Wish me luck!

Try the low pass filter first, then the gain. Aim for a large amplitude and only one sharp zero crossing per cycle. Use this scope to experiment!

The comparator won’t help - Tides’ CLOCK input is already a comparator (with a fixed threshold)! (Unless you can reliably adjust the threshold to be one of the peaks or trough of the waveform - but then you have to be very consistent in the amplitude of the notes you play).

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Testing out the configuration you suggested has led me to discover what I think is the main problem: due to the nature of the saxophone being a very long tube (albeit one with several curves to keep its overall size more manageable) no matter where I place the contact microphone on the instrument there is going to be an inevitable variance in the amplitude of the signal of the mic, leading to one waveshaping solution working for one register of the instrument but not another.

The best idea I can come up with on the spot is either using an offset to move the wriggly portion of the waveform above Tides’ clock threshold or using a preposterous amount of gain to make the wave as square as possible even if the amplitude varies. Sadly I don’t have either of those solutions in my rack right now so I’ll have to save up before I can test them in the field :cry:

Thanks again for helping me explore this really obscure problem, this has helped way more than all the current documentation I can find online of people attempting similar things!

i have no idea how mich this will help with a reed instrument but i run my bass guitar into tides once in a blue moon and i found it helps tremendously to apply aggressive compression. However i guess the main reason why this helps is that it evens out the amplitude of the notes played.
Anyway, give it a whirl!