Data AcQuisition And Real-Time AnalysisScope - Spectrum - Spectrogram - Signal Generator
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Noise Waves Overview
Noise Waves use random number generators to create data. There is a separate generator for each stream of each output, 8 in all. The generators used in Daqarta are technically "pseudo-random": They create what appear to be totally random values, but the exact sequence of values eventually repeats. However, since the repeat length is very long, there is no feasible way to tell that they are not totally random. How long is "very long"? The complete cycle is 2^63 or 9.22 * 10^18 samples, so if you create one value per output sample (say, with the White noise source), and the output sample rate is 48000 samples per second, then the sequence will take over 6 million years to repeat.
Since Noise Waves don't have any specific frequency like the regular repeating waves do, the main Tone Freq dialog is replaced with the Timing dialog. This allows options like Step (to hold each value for a selected number of samples), or Slow (to create an arbitrarily slowed version by interpolation). You can also add Smoothing, or Quantize the output to a reduced number of levels.
By the same token, since there is no repeating pattern in the random output, there is no particular interval upon which to sync the display. Instead, the Gen Sync period is controlled by the Step Size in the Timing dialog. This is the case regardless of whether the current Timing mode set to Spec, Slow, or Step.
Note, however, that Step and Slow timing do affect the noise spectrum, since they effectively slow the sample rate and thus cause aliasing: You will see a series of dips and decreasing peaks at higher frequencies. This may be of no consequence if you are using the slowed version as a controller for some other process, but it might be an issue for certain tests.
Since the random sources are really pseudo-random, there are also Timing controls that allow you to synchronize two or more generators, and to time-shift their output sequences relative to each other to produce delayed versions. Adding delayed noise sources together creates comb filtering or "jet sounds" effects.
Noise waves have less average energy than sine waves at the same Level setting. Consider that noise peak values appear only occasionally, while sinusoid peaks appear in every cycle. Gaussian and Pink noise have lower energy than White, since peaks are even less frequent. Band-limited noise is lowest; even with the band set as wide as possible to get a White spectrum, the waveform amplitude is only about half that of White, so energy is about one-fourth (6 dB lower).
See also Wave Dialog.
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