Data AcQuisition And Real-Time Analysis
Scope - Spectrum - Spectrogram - Signal Generator
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The following is from the Daqarta Help system:



Spectrum Analyzer

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Macro System

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Trigger Controls


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Play Wave Files Dialog

Controls: Gen Dlg >> Stream >> Wave >> Play
Macro: Wave=Play

This allows you to play an entire file as a signal source. It is similar to Arb, but with an important difference: Its length is completely arbitrary and may be as long as memory allows.

Where an Arb file is typically expected to contain a single cycle of the desired waveform, the Play file typically contains many cycles. Usually this is a complete recording of a complex sound that you want to manipulate, such as an animal vocalization, speech phrase, musical note, sound effect, or song.

Due to this difference, Play files use a Rate control instead of the standard Freq control. The playback rate may be up to 512 times higher than originally recorded, though high playback factors require greater CPU performance to handle the higher number of samples that must be processed.

Since there can be no meaningful Phase control with an unknown number of cycles of unknown frequencies, Phase is calibrated such that 360 degrees is 1024 samples at x1 Rate. As Rate increases, the time represented by these 1024 samples decreases proportionally. Phase thus represents a time offset in the Play file, equivalent to setting the Play From point to a different value.

Play files can use the same modulators as Arb files, but some controls behave differently. Phase modulation uses the above translation, such that 100% modulation gives +/-1024 samples of shift in the relative position of the waveform. Phase modulation can be used with Play files to create a "flanging" effect.

Frequency modulation is really Rate modulation, and there is an interaction between the FM Deviation setting and the basic Rate to keep things within range. Similar limits apply to Sweep.

Play uses linear interpolation to play back files at different rates. This is efficient, but it does introduce a certain amount of distortion due to the fact that the straight lines used for the interpolation don't always give a good fit to the true wave shape. In general, this situation is improved by using more points per cycle of the waveform, which gives a better fit. So the best situation for low distortion is when you record low frequencies or use high sample rates.

Play mode has its own dialog that allows up to 8 Play files to be loaded at one time. These files are available to any stream of either channel, and more than one stream can use the same file simultaneously but completely independently.

Macro Notes:

L.1.Wave=Play or L.1.Wave=6 sets Left Stream 1 Wave to Play, but only if a Play file is already loaded and selected for that stream. Note that this command may set Wave, but does not open the Play dialog. This is the usual approach for modifying Generator setups.

If the Wave dialog is already open, D.L.1.Wave=Play will open the Play dialog, and also set Wave to Play if there is a Play file loaded and selected.

When there are multiple Play files loaded, only one may be selected (button depressed) in any given stream. That is the one that will be activated by Wave=Play for that stream.

Loading a file to a given stream will also select it for that stream. The file will be present in all other streams of both channels, but not selected. To select it for a specific stream, use Play0=1 to Play7=1 as needed for that stream.

See also Wave Dialog.


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