Showing posts with label LFO Depth. Show all posts
Showing posts with label LFO Depth. Show all posts

Sunday, 6 July 2014

Limiting inspiration...

Sometimes the spark of an idea can come from a chance comment, and can tip your mind into thinking about something from a different viewpoint. One of the comments on Maxforlive.com for one of my comb-filter-based audio effects set me thinking, because it warned against using limiting because it could change the sound...

Now changing the sound is what audio effects are all about, and every time that I think there isn't any room for anything even remotely new, then up pops something that you hadn't considered before. So after a run of filter-based audio effects, I now had a nagging suspicion that there must be something that hadn't been explored with limiting (or its cousins, compression and expansion, and the evil twin, noise gating). Which is when a crazy idea popped into my head, and resulted in a series of limiter-based effects that reaches its natural conclusion in SyncLimiter.

It is often said that there is nothing new. So I'm cautious about suggesting that this might be new, so I will caveat this with 'new to me'. I've never seen anything that deliberately mis-uses limiting with LFOs setting the threshold, but then I'm a very conventional user of limiters (as in keeping something with lots of time-varying gain stable, as in a swept comb filter) and so I may well merely be revealing my blinkered knowledge.

So with all that out of the way, I present SyncLimiter, an audio effect that has two independent limiters whose thresholds and compression ratios can be modulated by sample-and-hold captured sine waveforms from two independent synch-able LFOs.


I've chosen the 'mirror' look for the UI, so the left and right hand sets of controls are reflected in the vertical axis. The first control to reach is the 'Limiter' control, which is just a lift from previous projects, and which does a complex mapping of threshold and ratio to give a single control that 'feels' right to me. At zero, there's only a slight effect, whilst at 100 there is maybe just a bit too much effect on the sound, and so the place to start is at a setting of about 50. (This is the default). After that, the 'LFO Depth' controls how much the LFO affects the Limiting, and the overall modulation is shown in the dark grey indicator. The 'S&H Freq' control alters the rate at which the LFO sine waveform is sampled (and held), and so at high frequencies (10 Hz) it has little effect, whilst at lower frequencies it chops the sine wave into a 'stepped' waveform. There's lots of scope for exploration here, with the relative ratios between the four frequencies, resulting in a wide variety of stereo changes to the sound. Some of the changes are subtle, others less so.

SyncLimiter works well on drums and rhythmic material like choppy comping. You may even like the way that it can muddle up pads, but using it on vocals is probably limited in its appeal. And actually, there are no rules - and any that you are given are probably interesting to try breaking. I'd be very interested to see in what ways this is mis-used!

I also apologise here to anyone who is offended by this flagrant exploitation of limiting, and I also have to warn users that there may be clicks present in the output of this effect, despite my best efforts with Max's 'line'. This is a dirty and crude effect - you have been warned!

As usual, SyncLimiter can be found at Maxforlive.com (One of these days I hope to make something different enough to get onto the Ableton 'Friday' blog entries!)

Sunday, 9 February 2014

A Limiting Solution part 1

Feedback comb filter structure
Feedback comb filter structure (Photo credit: Wikipedia)
Comber 0v01, my first MaxForLive comb filter suffers from a problem common to many systems with variable gain that include feedback. It has a tendency to go into oscillation, and because of the many modulation sources, the exact point at which it becomes unstable isn't easy to predict. Worse, the best sounds tend to occur just before it goes into the red.

One of the traditional techniques that are often used to solve this is to use a compressor or a limiter in the feedback loop, so that the gain variation is controlled. The implementations vary - one old method involved using an incandescent light-bulb and a light-dependent-resistor. Max provides library objects that do limiting and compression, but they have a User Interface (UI) issue: too many inter-dependent controls. Limiters and compressors are powerful tools, but adding lots of controls to Comber just to make it more stable would make an already complex UI even more busy. So how could I add the minimum of controls but keep lots of versatility?
I decided to try using one control to make several changes simultaneously in a limiter. As the input gain increased, the limiter threshold would be reduced, and the output gain would increase. This way, the maximum level stays the same, but the amount of limiting that is applied can be controlled. I also enabled one additional control for time response, and here the library object provided fast and slow modes. So I had one rotary control and one switch, plus a 'Bypass' switch to remove the limiter from the output.

The new controls could just be squeezed into Comber, and the testing showed that it made the effect much easier to use, although the limiting does alter the sound slightly, and on the higher settings, it does alter the dynamics quite a lot. And that's how Comber 0v02 was created!

Using Comber

Comber has a lot of controls, so here's a quick guide to getting the most out of it.

  1. Start with the Feedback controls set to zero, the LFO Depths set to zero, and the Pan Depths set to zero. Dry/Wet should be at 100% (Wet), Make-up Gain should be about 100%, and the Comb Gain controls should be at their default 50 position.
  2. Try the Comb 'Freq' (frequency) control. This moves the notches up and down in pitch, and can make big changes to the timbre of the input.
  3. Experiment with increasing the Comb Feedback controls from zero, and see how they change the sound.
  4. Use the LFO Depth control to move the Comb Freq(uency). Moving combs always sound much better than static ones! 
  5. The Pan Depth controls move the pan position of the two channels.
  6. The Limiter control starts out with no limiting at zero, and increases the amount of limiting (lower threshold) as you increase it towards 100. The maximum is a very non-subtle effect! 
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