Multitone Analyzer - Tektronix VM700T User Manual

Operating Basics

Multitone Analyzer

2–22
Most audio tests consist of measuring a sine-wave audio tone, then stepping the
frequency and repeating the test. The process continues until a measured level
versus frequency graph can be assembled and displayed. Each audio test
typically takes several seconds.
The technique is accurate and, where time is not an issue, is the best way to
perform an audio test. But when only a few seconds are available to perform a
complete measurement, or for adjusting a processing device, or nulling a
distortion, near-real-time updates of measurement data are necessary.
The VM700T Audio option Multitone Analyzer addresses this problem. Instead
of measuring a single-frequency sine wave, the Multitone Analyzer measures a
test signal consisting of sine waves at several frequencies. From the received
multitone signal, the Multitone Analyzer produces level versus frequency or
distortion plus noise graphs.
NOTE. The maximum amplitude of an individual tone in a multitone signal is
lower than it would be if it was the only tone sent. This lowered signal to noise
ratio affects the ability to accurately measure high signal-to-noise levels.
The Audio option Multitone Analyzer provides three types of graphical display:
View Levels – displays received signal level vs. frequency on a near-real
time basis.
View Difference – displays interchannel gain and phase differences for the
stereo pair.
View Distortion and Noise – displays the remaining spectrum after energy is
removed at frequencies near the multitones (this display contains only noise
and distortion products).
Figure 2–12 shows the Multitone Analyzer level versus frequency display.
VM700T Option 40/41/42 Audio Measurements User Manual