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!

Conceptual Spectrum Analyzer

To apply the Sine Wave Analysis principles to analyze an unknown input signal, it seems that all we need to do is multiply it by a unity amplitude reference wave with adjustable frequency, average the product to extract only results from matching frequencies, double each average to get the input amplitude, and plot this amplitude versus reference frequency to get a spectrum.

This is basically a good approach, but there is a slight complication: The sine product formula works for sine waves "in phase", which means that both waves must start from zero at the same time. The averaged product only tells us about the amplitude of a signal with that exact same alignment. If the signal starts a little earlier or later than the reference wave, even if its frequency is the same, the constant value will be reduced and likewise our measurement of the signal amplitude. If the signal is a cosine wave, the measured amplitude will be zero. Since in general the reference wave won't have any fixed phase alignment with the signal wave, this is a serious problem.

Next: Practical Spectrum Analyzer


See also Spectrum (Fourier Transform) Theory

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