SP395 SoundPro Audio Integrator Form7492 Operation Manual
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Distortion Meter
The Distortion Meter analyzes audio equipment for distortion. There are two separate distortion
measurements supplied, THD+N (total harmonic distortion plus noise) and IMD (inter-
modulation distortion).The SP395 measures THD+N of an incoming signal by comparing the
level of the incoming signal sine-wave with the level of harmonics and noise. It measures IMD
by comparing the level of an incoming multi-frequency test tone to the level of its inter-
modulation distortion components.
Distortion Meter Display Screen and Controls
The Distortion Meter tests have slightly different control test screens. The THD+N display
screen contains all the generator toolbar icons at the bottom right. The IMD test requires special
two tone output signals which are supplied from the SP395’s internal generator. In the IMD test
function, the generator toolbar signal type and frequency selections are removed. The signal type
for the generator is selected automatically with the test type selected, either DIN 250/8k or
SMPTE 7kHz/60Hz. The metered test results are displayed the same.
THD+N Description
The Distortion Meter may be used in conjunction with the internal generator or with a separate
low distortion generator. The SP395’s THD +N test is designed to be performed at 63, 125, 250,
500, 1000, or 2000 Hz. The THD+N test sums the energy in the harmonics (and residual noise)
of the sine-wave audio input to the meter to compute the THD+N. The range is 0.02% to 50%.
The display shows the numeric test value, and also has a bar-graph using a log-scale from 100%
to 0.001% THD.
Note: You may use the SP395’s internal sine-wave generator or an external low distortion sine-
wave audio generator along with the SP395’s distortion meter. Be sure to choose a generator
frequency which matches the test frequency of the SP395’s Distortion Meter.
THD +N test screen and description of control fields.
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