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filter in one of the auxiliary filter sockets. With a 1 kHz fundamental
frequency, for example, a 3 kHz filter (FBP-3000) will be used. Select
THD+N function with WTD response and the optional filter selected.
The THD+N indication is then 3rd harmonic distortion ifthe generator
frequency is 1 kHz.
Compact Disc Players
All tests ofCD players must be made while playing specially-recorded
test discs carrying the proper signals.
Frequency response is preferably measured while playing a track with
a sweep tone across the entire band. Many test discs have a sweep of
about 50 seconds duration across the audio band which is suitable for
Portable One Plus Access. LEVEL function with dBr units should be
selected. Select SWEEP mode, and further select EXTERNAL mode
with the top center soft key and GLIDE with the top right soft key.
Play a mid-band (typically 1 kHz or 997 Hz) reference track (often
such a signal is recorded at the beginning ofthe sweep track) and press
the “dBr ZERO” button to set the reference. Then, press the SWEEP
button to start measurements and start the CD player. Portable One
Plus Access will acquire and plot measurements across the audio band.
Ifthe following track has a mid-band signal such as 1 kHz, the reversal
in direction offrequency change will automatically terminate the test.
Alternately, the test may be terminated by pressing the SWEEP button
again when the numeric display at the left of the graph or the CD
player display indicates that the sweep track is finished. If a test CD
with sweep tone is not available, a series of tracks at different
frequencies and fixed amplitude may be used.
THD+N versus frequency of CD players is measured in SWEEP
EXTERNAL mode and THD+N function, using a series of full
amplitude test tracks at different frequencies. The analyzer
automatically selects AUTO-TUNE mode so that the THD+N notch
filter is steered by the frequency counter. The 22 Hz-22 kHz bandpass
filters should be used in this application. Each channel of the CD
player must be tested separately, since THD+N function measures
only one channel at a time.
5
A
pplications
Compact Disc Players
Applications
Portable One Plus Access User's Manual
5-5
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