The above image was obtained with a Sound Blaster 16 using the SB16.ADC driver to produce separate tone bursts on the Left and Right output channels. These outputs were combined externally via two 10K resistors and routed to the Left Line input to produce the trace shown.

The SB16 driver controls the on-board OPL3 synthesizer chip to produce the tone bursts. The right side of the screen shows the Right Synth control menu setup to produce the second tone: Burst mode, 2000 Hz Frequency, 220 sample Delay from the start of the sweep sync point, 1.00 msec Rise time, 100 sample "on" Duration, 1.6 msec Fall time, and -15 dB Level. The Left Synth was set to Burst mode, 1000 Hz Frequency, 0 Delay, 1.00 msec Rise, 100 sample Duration, 3.1 msec Fall, and -9 dB Level.

Besides Burst mode, either or both tones may be set to continuous On. Since the synthesizer is completely independent of the CPU, tones can continue whether Daqarta is in RTime or Sequential mode (unlike the STIM3A or STIM3 Stimulus Generator modules, which can only produce continuous tones in RTime mode).

There is also a Gap mode, which is the opposite of a tone burst in that the tone is normally on, and goes off for the specified Duration.

In addition, there is a special undocumented feature of the OPL3 that can be used to generate broadband noise instead of tones, either continuously or in bursts or gaps. The SB16 driver will perform the operations needed to activate this mode whenever a negative tone frequency is requested. However, this feature is not supported by all Sound Blaster models beyond the SB16, and on some individual cards it may occasionally produce noise with a DC offset. (That may not be a problem for continuous noise, due to the AC-coupled output of the synthesizer, but it produces unacceptable thumps in Burst or Gap modes.)

On earlier mono sound cards using a single OPL2 synthesizer, there is only one output channel. Otherwise, the controls are much the same as indicated. 8-bit cards, whether mono or stereo, also lack decent Level controls. The SB16, on the other hand, is absolutely suberb... its accuracy and linearity rival many laboratory attenuators. Since the Level controls operate on the analog output signals (rather than reducing the digital values going into the DAC as with the STIM3 Level controls), the dynamic range can easily exceed 120 dB without compromising signal distortion.

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