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Modulating Burst Values

Macros: BurstLagMod, BurstRiseMod, BurstHighMod, BurstFallMod, BurstCycleMod, TrainCountMod, TrainCycleMod

The small buttons to the left of the main Burst controls open separate Burst Time Modulation dialogs for each value. Burst Time Modulation refers to modulating the durations of the individual Burst stages. Please don't confuse this term with ordinary Burst operation, with involves a modulation of the amplitude of the main wave.

Consider a very slow sine wave modulator, much slower than the Burst Cycle... say 10 times slower, or 10 seconds per cycle (0.1 Hz) where Burst Cycle is 1 second. At the start of a burst cycle the instantaneous value of the modulating wave is sampled. This is then scaled down by a Depth percentage and multiplied by the base value of the burst interval being modulated, and added to the base value to get the actual value used.

For example, if the base High value is set to 0.6 second and Depth is set to 40 percent, when the modulator is at its positive peak (+100%) it is scaled down to +40% and multiplied by 0.6 second to give 0.24 second, which is added to 0.6 to get a maximum High value of 0.84 second. When the modulator is at its negative peak, the minimum High value is 0.6 - (40% * 0.6) = 0.36 seconds.

The net result is that the High interval undergoes an increase and decrease in a sinusoidal pattern over a 10 second period. If the Burst Cycle is fixed at 1 second, there will be 10 bursts in that time, with each High duration corresponding to a point on the modulating sine wave.

You can apply the full range of modulation options to any or all of the burst phases, modulating with anything from a simple sine wave to another Stream or combination of streams. The other streams can be waves of any type, including random or pre-recorded Arb or Play files, and they may have modulation of their own.

TIP: The instantaneous modulator value at the start of the burst interval is used to determine the interval; once started, an interval continues until it is done, no matter what the modulator does in the meantime. If the modulator changes too quickly, the next burst will catch it at a point in another cycle that doesn't seem to follow the prior point. So, if you want the modulated burst interval to accurately follow the modulation source, that source should be much slower than the burst cycle. Typically, you should have multiple bursts per cycle of the source.

On the other hand, if you want to produce intervals of random duration, you can use a noise source as the modulator. You don't need to slow it down, since the instantaneous value at the start of the interval will be a good random value.

To see how burst modulation works, start with a simple "beep" series with High set to 0.5 second and an overall Burst Cycle of 1 second, with Rise and Fall times of perhaps a few msec. Set Train Count to 1 and Train Cycle to minimum.

Now click on the High button to open the High modulator. The Mod button at the top of that dialog activates the modulation. The next button is just a copy of the ordinary High control, for convenience. Below that is the Mod Source control, which defaults to Sine. Under that is the Depth control, which defaults to zero for no change at all.

Activate the modulation by toggling the button at the top of the dialog. There should be no change in the sound, since Depth is set to zero. Set Sine Mod Freq to 0.1 Hz, and Depth to 50%. Now the lengths of successive beeps should slowly change longer and shorter over a 10 second cycle. Instantaneous depth appears in the box below the Depth control.

The Mod Source button opens a dialog that allows you to use one or more of the other Streams of the same output channel as the modulator source.

The dedicated Sine modulation source is much more efficient than using another stream, but note that it is only a single source used by all stages of a burst stream. This is an advantage if you want all stages to change together with perfect tracking; otherwise, you will need stream modulation.

Different stages can have different depths, but all that use the Sine source share the same frequency and phase, with one exception: The depth variable accepts negative values, which gives the same effect as setting the phase 180 degrees from the indicated value. This can be useful where you may want an increase in one burst interval to be balanced by a corresponding decrease in another to maintain a fixed total cycle. Of course, you can use this same trick with stream modulation as well.

One advantage of using stream modulation with Multi-Channel Output mode is that, unlike normal stereo, the modulator stream itself can be used as an output. This can be used to supply a modulation sync signal to an external device.

Macro Notes:

If the Burst Dialog is open, BurstLagMod=1 opens the Burst Time Modulation dialog, BurstLagMod=0 closes it, and BurstLagMod=x toggles between open and closed. BurstRiseMod, BurstHighMod, BurstFallMod, BurstCycleMod, TrainCountMod, and TrainCycleMod work the same way.

Note that you do not need to open a Burst Time Modulation dialog to set its controls directly via macros. But since the same basic controls are used for each modulator, you will need to use a prefix (in addition to the usual sample and stream prefixes) to specify the modulator: Lag., Rise., High., Fall., Cycle., Count., or Train.. See examples for individual controls.

See also Burst Time Modulation Dialogs, Burst Button, Burst Overview, Basic Burst Operation, Burst Controls, Waveform Stream Controls.


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