Blink 183 - Monitoring LFO for slow tap tempo

[Mark Hammer]

I had expressed some frustration earlier in the fall with the visual monitoring of tap tempo for slow vs fast LFO sweeps.  If you followed that thread (dear lord, I need to learn how to use the search feature! ), you will know that some suggestions cropped up including a brightness "swell" over the LFO cycle as well as assorted multi-LED "visual metronomes".  The basic underlying principle was that when the LFO speed is fast enough to follow or anticipate in your head, you can mentally imagine where the cycle is at right now and tap your foot appropriately to set the intended speed.  Once the sweep cycle gets long enough, though, it gets harder to imagine where the cycle is at right now, and harder to strategically tap your foot on any tap tempo switch.  Especially in the absence of any visual feedback to aid the imagination.

On Monday, I was pleasantly surprised to receive a bunch of modules from the very kind Jeorge "Mr. Huge" Tripps over at Line 6, one of which is the production version of the Liqui-Flange.  I had played with the prototype over the summer, but hadn't touched one since late July and hadn't seen/tried the production version yet.  I'm not sure whether this feature was built in already at that time and I overlooked it, or whether our collective whining here made a difference, but I am very pleased to report that the status LED on the Liqui-Flange now does what I wanted it to do.  Instead of simply blinking briefly at the "turnaround point", it gradually glows brighter over the sweep cycle.  While perhaps not as useful for keeping track of a 12-second sweep as something like a rolling 10-LED meter-display might be, it is pretty much as useful as a single LED can be, and really helps a lot for planning out taps.  Thanks to Jeorge and Angelo.

One of the slightly more useful LFO displays I've seen is one that Mike Irwin implemented on one of his more complex phasers.  Here there are two different-coloured LEDs, one for one half cycle of the sweep, one for the other.  It's been a couple of years since I've seen that one, so I don't remember whether it simply flashed or whether it swelled as the Liqui-Flange display does.  In some respects, the ideal compromise of space, complexity, and functionality might be a 2-LED or bi-color LED display that swelled in brightness and switched colors at the crossover point (halfway during the descent, and halfway during the ascent).  The general idea is to be able to anticipate the turnaround point for setting speed, either by means of tap tempo or by manual control.

[free electron]

An analog VU-meter would be nice as LFO display
P.

[Mark Hammer]

Yes it would be.  A bit like an LED display with infinite resolution (instead of 10 or even 20 segments).  Of course fitting it in the allotted space might prove tricky.

Imagine the following wet-dream.  A rackmount phaser, flanger or other modulation effect.  There are two modulation sources onboard, each of which can be "reset" to the beginning of their sweep cycle.  Each has an associated VU-type meter on the front panel so you can see where each is in the sweep cycle right now.  Beside them is a 20 segment vertical meter type LED-indicator that shows their sum.

As we've seen on oh so many fronts, happy implementation is often a function of dependable intelligence.  KNowing what your LFOs are doing right this instant is always useful for planning out sweeps.

[Peter Snow]

In some respects, the ideal compromise of space, complexity, and functionality might be a 2-LED or bi-color LED display that swelled in brightness and switched colors at the crossover point (halfway during the descent, and halfway during the ascent).

Hi Mark,
I did that with the LFO on the first synth I built (over 20 years ago!). It sounds similar to what Mike did with his phaser. I used the standard dual op-amp triangle/square LFO with red and green LEDs on the square wave output. The LEDs were connected in opposite directions so the red one reacted to the negative part of the wave cycle and the green to the positive part of the cycle.  I think in my supreme ignorance I simply connected the LEDs directly to the output of the LFO with limiting resistors to ground.  Heaven knows what that did to the integrity or amplitude of the waveform but in those days I was happy when something worked and I did not have time for the subtle details

When connected to the square out, the LEDs gave a visual indication of the speed of the LFO and which part of the cycle it was on. First the red LED came on then it would go out as the green one came on, etc, etc.  It was more useful when connected to the triangle wave as the LEDs would gradually increase and decrease in brightness as each part of the wave cycle came and went.

I am a sucker for flashing lights so if I was to build another similar device I would have indicator LEDs all over the place

Cheers,

Peter

[free electron]

Imagine the following wet-dream.  A rackmount phaser, flanger or other modulation effect.  There are two modulation sources onboard, each of which can be "reset" to the beginning of their sweep cycle.  Each has an associated VU-type meter on the front panel so you can see where each is in the sweep cycle right now.  Beside them is a 20 segment vertical meter type LED-indicator that shows their sum.

Then, add for each: tap tempo function with time scale switch, hypertriangle/sin/triangle/square/ADSR/random selectable waveform,  mentioned two Reset inputs (footswitch), Voltage output with Level controls, MIDI interface (setting the tempo, waveforms, resetting via midi), then build line of stompboxes with external modulation control possibility...
It looks difficult, but with some skills in programming all that can be done with a cheap microcontroller. It's just a matter of time and need.
Some years ago I was thinking about building another kind of modulation pedals,  controlled not  by lfo, but with stomp-triggerable ADSR generator. Even simple Attack-Decay generator made with 555 could be nice as additional feature in any kind of modulation efect.
P.

[GFR]

An analog VU-meter would be nice as LFO display
P.

Or an "analog clock" display with a pointer rotating 360 degrees at each cycle.

[Processaurus]

I've been thinking about an LFOish thing where theres a couple momentary switches for changing direction on the LFO, example:  it rises up, you hit a switch to change direction, it goes down, and stays at the bottom of the sweep till you tap the change direction button again.  Way dumber than tap tempo, except you're not at the mercy of a repetitive waveform, and could really work it into a part.  you could even set or reset the waveform while the pedal was bypassed, I hear some people using modulation pedals briefly for transitions between parts, so they could just have ,say, a brief falling sweep that would behave itself.  Graham Coxon does that kind of thing, I forget what song it is but he flanges up just for the second half of a measure, and keeps doing it (naturally it sounds totally awsome).  When asked how he does it (live too), he says he just got really good at setting the speed .

[Dave_B]

Sounds like you're switching out the LFO with a latching Attack-Decay circuit.  I've seen an A/D that uses a flip-flop (cd4013?) to switch from Attack mode to Decay mode.  I haven't thought it all through, but a switch could be used in place of the comparator to switch it manually.