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

# Octaves Frequency Entry Step Mode

Controls: Gen Dlg >> Stream >> Tone Freq >> Step Mode >> Octaves
Macros: Fstep, FstepOct

This mode may be selected from the Frequency Entry Step Mode dialog, which opens via the Step mode button that indicates the current mode. That button is located under many frequency entry controls in the Generator. The mode setting applies to most Generator frequency entry controls. The mode only affects values during entry or adjustment; it does not change previously-entered frequencies.

It is often useful to work with octaves rather than linear frequencies. The term "octave" derives from music theory, where a step of 8 "whole notes" (white keys on a piano, say from one C to the next higher C) represents a doubling of frequency.

The exponential nature of the human auditory system means that a change from 220 to 440 Hz, for example, sounds the same "size" as a change from 440 to 880 Hz.

Many physical systems have responses proportional to frequency or a power of frequency; a filter whose response falls proportional to 1/f will have its output voltage halved (-6 dB) for each doubling (octave) of frequency. This accounts for the common 6 dB/octave response spec of simple filters.

The Octave mode thus allows frequency changes to be made in this ratio fashion, expressed in octaves and fractions thereof. If the current frequency is 500 Hz and the Octave step size is set to 1.0000 (default), then scrolling the frequency up one step will give 1000 Hz, or scrolling down will give 250 Hz. If the step had instead been set to 0.5000 octave, the resulting frequencies would have been 707.107 and 353.553 Hz.

Octave mode allows direct entry of any arbitrary value; no quantization is applied. Only during scrolling is the octave step applied, and the result is always relative to the original value.

Macro Notes:

Fstep=Oct or Fstep=3 sets Octave Step Mode.

FstepOct=0.5 sets the step size to 0.5 octave.

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