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

Features:

Oscilloscope

Spectrum Analyzer

8-Channel
Signal Generator

(Absolutely FREE!)

Spectrogram

Pitch Tracker

Pitch-to-MIDI

DaqMusiq Generator
(Free Music... Forever!)

Engine Simulator

LCR Meter

Remote Operation

DC Measurements

True RMS Voltmeter

Sound Level Meter

Frequency Counter
    Period
    Event
    Spectral Event

    Temperature
    Pressure
    MHz Frequencies

Data Logger

Waveform Averager

Histogram

Post-Stimulus Time
Histogram (PSTH)

THD Meter

IMD Meter

Precision Phase Meter

Pulse Meter

Macro System

Multi-Trace Arrays

Trigger Controls

Auto-Calibration

Spectral Peak Track

Spectrum Limit Testing

Direct-to-Disk Recording

Accessibility

Applications:

Frequency response

Distortion measurement

Speech and music

Microphone calibration

Loudspeaker test

Auditory phenomena

Musical instrument tuning

Animal sound

Evoked potentials

Rotating machinery

Automotive

Product test

Contact us about
your application!

Sound Card Spectrum Window Toggle

Controls: Spectrum Dialog >> Window
Macro: SpectWindOn

This button applies a window function to the raw waveform data before computing the spectrum. You can toggle this from the keyboard via ALT+W even when the Spectrum dialog is not active.

An optional BW Corr (Bandwidth Correction) button just below the Window button allows you to select true energy scaling instead of best peak amplitudes. The window function itself is selected using the six radio buttons at the bottom of the Window groupbox.

The FFT (Fast Fourier Transform) that is used to generate the Spectrum display can give misleading results when signal frequencies don't fall exactly on the analysis frequencies of the FFT. The 1024-point FFT used here provides 512 analysis frequencies, spread evenly from 0 hertz to the Nyquist frequency (half the sample rate).

The FFT only provides information about the amount of signal at each of these analysis frequencies. When a signal component falls between two analysis frequencies, each will show a partial response. But in addition there will be leakage responses at many adjacent frequencies, which on the display will appear as "skirts" draping away from the true frequency peak. A window function, applied to the waveform before computing the FFT, can reduce these leakage skirts, but there is a trade-off among the various possible window functions: Functions that most reduce the leakage will also broaden the response near the true peak.

You don't need a window function when the signal is generated using the Lines option for setting the Generator sine frequency, since it is exactly synchronous and produces no leakage skirts.

You also shouldn't use Window when the signal is broadband noise (no tone peaks), or when analyzing transients that fit entirely within the 1024 samples used by the FFT.

See Spectrum Window Theory for a complete discussion.


Macro Notes:

SpectWindOn=1 activates Spectrum Window, SpectWindOn=0 turns it off, and SpectWindOn=x toggles between on and off.


See also Spectrum Control Dialog

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