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Precision Swept Sine Measurement Mode

Swept Sine Measurement mode for high precision (in amplitude and frequency) measurements; resolution can be specified in Hz, fractions of an octave or decade; single or dual channel.

Above: calibrated frequency response measurement, straight wire connection (sound out to sound in)

  • Calibrated (an automated procedure) single-channel amplitude accuracy within +/- 0.02 dB, 20 Hz - 20 kHz (Waavebox test signal used for calibration and measurements)
  • Calibration compensates for computer sound hardware frequency response
  • Two-channel measurements: gain balance and flatness within +/- 0.001 dB, 20 Hz - 20 kHz
  • Sweep tracking, time-domain filter rejects out-of-band signals

Why bother with antiquated, swept sine measurements - aren't FFT methods "better?"

The choice of measurement technique depends on the frequency range and amplitude accuracy required in the measurement application.

When maximum accuracy and precision (in frequency and amplitude) are needed, swept sine measurements are superior to FFT based techniques! FFT scallop loss and window leakage (when the test frequency does not exactly match the FFT frequency "bin") limit FFT amplitude accuracy. FFT frequency measurement "bins" are linearly spaced - a swept sine measurement may be configured for linear or logarithmic measurement frequency steps; the step size is at the discretion of the user (not the software designer).

Mac the Scope, in combination with Waavebox, provides the user a choice between Swept Sine and frequency-domain spectrum analyzer techniques.

Example of application of Swept Sine measurement mode

Measurement of audio equalizer (Audio Control model 520, series B; serial number A10100), 1 kHz filter at various boost and cut settings. Sweep started at 10.0 kHz, sweep frequencies calculated at exact 1/6 octave multiples of start frequency. The circles indicate the frequencies where the response was measured (same for all curves, shown only for response extremes).

Example of application of Swept Sine mode: high-resolution (frequency and amplitude) measurement

1 / 2000 octave resolution (and < 0.01 dB amplitude settling resolution) single channel measurement of same audio equalizer 1 kHz filter, maximum boost setting as above.

The filter center frequency was determined from the plot to be 1029 Hz.

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