Daqarta Generator modulators such as AM, FM, and Phase/Width/Slope allow a selection of modulation sources. This ability is also provided for individual Burst duration parameters, as well as for Timing Quant, Bias, and Shift.

Hitting the Modulation Source button pops up a list of the available sources. Although the default is a sine wave with adjustable frequency and phase, you can select another stream output or combination of streams as the Source.

On Stream 0, Sine is the only option. On Stream 1, you also have the option of selecting Stream 0 as the source. Higher streams allow all lower streams, plus all combinations: Stream 3 allows 0, 1, 0+1, 2, 0+2, 1+2, or 0+1+2.

When you select another stream as a Source, the Stream On control at the top of its Stream Dialog changes to Stream Mod, indicating it is in use as a modulator source only and does not go directly to an output. That condition remains as long as that stream is selected as a Source by any modulator on any stream, even if that other modulator or stream is inactive.

A stream that has been selected as a source may be toggled off and on at any time. The Stream Mod (formerly Stream On) control will still say 'Stream Mod', but it will be shown depressed if the stream is active as a modulator. When the stream is off, it provides a "zero modulation" source to the modulator. This allows you to quickly select from among multiple sources, or lets you see the effects with and without modulation.

When a stream is selected as a modulator source, it can be shared by other modulators of different types or on other streams.

The Mod Freq and Phase controls are disabled in the current modulator when the Source is no longer set to Sine. Instead, you use the main Tone Frequency and Phase of the selected Source stream or streams. The Depth or FM deviation control on the modulated stream works normally. The Level control on the Source stream works in tandem with this to provide the total modulation amount. When you combine two or more streams together to serve as a source for a single modulator, the source Level controls allow you to set the relative proportions of each stream, and the depth control on the modulated stream sets the overall amount.

You can cascade modulators together on the same Left or Right channel, such that L.0 Stream controls a modulator on L.1 Stream, and the output of 1 is the source for a modulator on L.2 Stream, and that output is the source for a L.3 Stream modulator.

This is an extremely powerful and flexible option. You can use it to create noise bands with FM or Sweep (which are not allowed directly). You can use Arb or Play files as sources and step through them slowly to act as test controllers. You can use a random source to select from among a particular range of values (phases) in an Arb file to get a random selection of known values instead of just random values.

Suppose, for example, you want to create a frequency sweep that goes up and back down again repeatedly. (The standard Sweep modulator is unidirectional.) You can use a Triangle wave as the FM modulator Source, if you want the up-sweep and down-sweep to have equal durations, or the Ramp source if you want them to differ.

Now suppose you want an exponential bi-directional sweep. To do this, load the Expnote.DAT Arb file and select it as the Wave for L.1 Stream. This file contains, besides several musical scales, an exponential curve extending from a phase of 144 to 360 degrees. Use a Triangle or Ramp on L.0 Stream as the source for the Phase modulator on L.1 Stream. Set the L.1 Stream main Freq to 0, and the Phase to 251.5 degrees (near the center of the exponential portion). Now the L.1 Stream output will be a level exponentially related to the instantaneous L.0 Stream ramp output.

Set the L.1 Stream Phase Modulation Depth to 50%, and the main L.0 Stream Level to about 60%. This will cause the L.1 Stream phase to run over the entire exponential range. To insure you have the proper Depth, Level, and Phase values, set the L.0 Stream Freq to about 100 Hz and monitor the L.1 Stream output. You should see a U-shaped wave that goes down almost to zero and up almost to positive full-scale. If you set any of the adjustments too far off, you will run into another part of the Expnote.DAT tables and see a spike at either extreme of the waveform.

Now set the L.0 Stream Freq to the actual sweep cycle rate you want. Set L.2 Stream main Freq to slightly less than the lower end of the desired sweep range (since the exponential curve doesn't go quite down to zero), set the FM Source to L.1 Stream, and set the FM Deviation +/-F to the upper limit of the desired sweep. Note that although this is shown as plus and minus, since the modulator is only positive you are only using that half of the range.

Or, you can create a custom Arb that includes a single cycle of any sweep shape, and use it to drive the FM modulator directly. Or a Play file with a whole series of different sweeps to act as a test scheduler.

TIP: If you don't need all four streams for your modulation setup, make stream 3 the final stream and leave the streams starting with stream 0 unused. That way, if you later want to add another modulator, you can use lower streams to modulate higher streams... but not the other way around.

Whenever you are trying to figure out how to set up a really complex signal or test, chances are that Stream Modulation can provide the solution.

The Composer.GEN setup is a good example of several stream modulation techniques.

See also Waveform Stream Controls.

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