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Sound Card Basic Burst Operation

Consider the basic "beep, beep, beep..." burst operation. To learn how to use the various controls, start out with the Left output at a comfortable listening volume and set for the default 440 Hz Sine wave on Stream 0. Make sure Trigger is active and set to Gen Sync.

Click on the Burst Modulation button on that stream, which will open the Burst control dialog. Click on the Burst button at the top of the dialog to activate the burst operation. The timbre of the tone will deepen to sound something like a low brass instrument. The display will change from the original simple sine wave to one with the same general alignment but a bobbing amplitude.

Toggle the Train Sync button on, and the display will resolve to show a burst, followed by a pause and the start of the next burst.

The Samples/Seconds button can be toggled to allow either units when viewing or setting the various intervals. Intervals are always in multiples of a single sample period, even in Seconds mode. For short intervals, the integer values of Samples mode may be easier to deal with than several decimal places of fractional seconds. (But note that even though seconds are displayed as decimals, you can always enter values using prefixes, like "1m" for 1 millisecond instead of entering "0.001".)

Burst Shape controls the shape of the Rise and Fall portions of the burst. Leave this at the default of 2 for now.

For the moment, ignore the small buttons to the left of the other controls. They open dialogs to modulate those values.

The output signal starts out in the silent state, and stays there for the interval specified by the Burst Lag control. This is typically set to zero, so that the burst starts at the start of the cycle and hence the start of the display.

The Rise control sets the interval over which the signal rises up from off to on. Slower rise (larger interval) means less spectral splatter (less-noticeable turn-on click).

High sets the duration that the burst stays fully on.

Fall sets the interval over which the signal falls back from on to off.

Burst Cycle sets the overall burst repeat interval. The lowest value you can set is the sum of the Lag, Rise, High, and Fall intervals, which means the next burst cycle starts immediately after the end of the Fall interval. Normally you will want it larger, to space the bursts farther apart.

Burst Cycle will be forced to a higher value if you increase one of the other settings too much, since it must always be at least as big as the sum of the preceding stages.

To go from our deep brass timbre to discrete beeps, you must increase the High and Cycle times. Try setting Burst Cycle to about 1 second. (Hint: Use Seconds mode and enter '1'.) You will hear a "knock" once per second. Now increase High to (say) 0.5 second to hear "beep, beep...".

Experiment! Try setting High to zero, and you will hear a knocking sound. Increase Fall to 0.5 second and it sounds more like striking a metal tube. Increase Rise to 0.5 second as well, and it sounds like the sound is sweeping past you.

Below the Burst controls are the Train controls. These allow the Burst cycle to be repeated an arbitrary number of times, as set by the Count control, after which there will be silence to give an overall Train Cycle interval before the whole process is repeated. Try setting Count to 3 and Train Cycle to 4 seconds. With each Burst Cycle at 1 second (say), you will hear 3 bursts one second apart, followed by a second of silence, and then repeat.

Train Cycle will be forced to a higher value if you increase the Count or one of the Burst settings too much.

ENVELOPE-ONLY TRICK: Sometimes instead of an actual tone burst, you may want the Stream output to be only the envelope shape that would otherwise be applied to a tone to create a burst. You might want this, for example, to use as a modulator source for another stream, such as to smoothly control frequency or phase.

To do this, set the Wave type to Sine and the Tone Frequency to zero. Set the Phase to 90 degrees, which is where the sine wave is at its maximum. Since the frequency is zero, it stays at maximum. This creates a DC level to apply to the Burst generator, which will shape it accordingly.

See also Burst Button, Burst Overview, Modulating Burst Values, Burst Controls, Waveform Stream Controls, Burst Application: Auditory Evoked Responses, Burst Rise/Fall vs. Spectral Width.


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