Overview; Audio Spectrum Display - Tektronix SPECMON3 Manual

Audio Analysis

Overview

Audio Analysis measures basic time- and frequency-domain parameters of analog audio signals modulated
on a carrier (AM, FM and PM modulation) or unmodulated (non-carrier) audio signals (Direct).
For modulated signals, the measurement analysis first demodulates the signal to provide the Audio signal
waveform. Direct input signals bypass the demodulation step. For FM and PM demodulation, the carrier
frequency error is estimated during demodulation.
The Audio signal waveform excursions are then measured to determine the Peak and RMS waveform
parameters. Next, the analysis detects the highest-amplitude frequency component within the audio
bandwidth, and makes a high-accuracy frequency measurement of the frequency component. This value is
called the Audio Frequency.
A spectral analysis of the Audio signal waveform is performed to determine the presence and level of
harmonically- and/or non-harmonically-related narrowband spurs and wideband noise. The Audio
signal, harmonic and non-harmonic spurs, and noise level data are combined to produce signal summary
parameters including SINAD, Modulation Distortion, Signal-to-Noise, Total Harmonic Distortion, and
Total Non-Harmonic Distortion.
Controls are provided to allow the user to select audio filters of Low Pass, High Pass, FM De-emphassis,
or Standard-defined response, as well as completely user-definable filter response. Filtering can be applied
as needed to modify the audio spectrum result before measurement to remove unwanted spurs or noise.
Flexible control parameters are provided to allow setting the Audio Bandwidth for analysis, the Resolution
Bandwidth (RBW) and RBW filter type of the spectral analysis, and number and level qualifications for
Harmonic and Non-harmonic spur detection. Multiple-spectrum averaging can be enabled to provide a
smoothed spectrum for results with less variability than single-spectrum results.
The Audio Spectrum display shows the frequency spectrum waveform with detected harmonic and
non-harmonic components identified by markers, and a corresponding table of frequency and level values
for the spur components. The markers and table provide easy visualization of the significant spurs and
their relation to the fundamental Audio frequency signal.

Audio Spectrum Display

The Audio Spectrum display shows audio modulation characteristics. You can choose to show just the
spectrum of the audio signal or show the audio spectrum of the signal and the results of distortion
measurements. The Audio Spectrum display can show a table listing the frequency of a Harmonic
Distortion (HD) and Non-Harmonic Distortion (NHD) and its level. The Spectrum graph indicates these
harmonics and non-harmonics with special markers.
To display the Audio Spectrum display:
1. Press the Displays button or select Setup > Displays. This shows the Select Displays dialog box.
2. From the Folders box, select Audio Analysis.
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Overview
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