Lindos LA100 - LA101 Weighting Curves; User Weighting Curves

tone testing.
2.26 LA101 Weighting Curves CCIR468 inverse Oscillator weighting User weighting curves Pre-emphasis
on the LA101 cycles round weighting curves, currently RIAA-inverse, 50µs pre-
emphasis, CCIR468-inverse and CCITT O.41 psophometric inverse weighting for testing
disc pre-amps, FM transmitter systems and noise weighting filters. All levels are
generated digitally with high accuracy from look-up tables which are currently limited to
third-octave frequencies. The level can be adjusted using the
keys as usual,
and the weighting for the current frequency will be added to the displayed level to
calculate the actual output level. Excessive output excursions will cause the output level
to ‘slide’ to a value that can be managed. The level can be reduced when testing RIAA
phono inputs by setting a level of, say, -60dB; but it is sometimes better to use a potential
divider close to the input, as this also reduces stray pickup. A test with 50k
series
resistance is often also useful in showing up input impedance variations. Test levels are
still operative with weightings.
In addition to the existing weighting curves provided in the LA101, user weighting curves
can be entered. Pressing
in manual mode will normally cycle through the available
weighting curves (but see below):
W1-W5 User weighting curves
W6 RIAA inverse (disc recording characteristic)
W7 CCIR 468-3 inverse
W8 O.41 CCITT inverse
W9 50µs pre-emphasis
For quick access to a particular weighting curve configuration W can be set to one of the
above weighting numbers to make
toggle between that weighting and the flat
unweighted state. Setting configuration W0 (the default) will make
cycle through
all of the defined weightings. Only third octave frequencies can be used when a
weighting curve is in use and the weighting is applied equally to both left and right
channels.
2.27 User Weighting Curves De-emphasis Define weighting curve Inverse response Pre-emphasis
User weighting curves are useful for testing filters using the inverse filter response which
should result in a flat overall response. They are also useful for making test tapes where
the inverse of the record response is entered as a weighting curve to obtain a flat response
recorded on tape. User weighting curves, like pre-programmed weighting curves, can be
used to generate weighted frequency sweeps − see section 3.19.
To define one of the user weighting curves in the LA101 hold
and press and
then enter the weighting number (1 to 5), see figs. 2.25 and 2.26.
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2. Manual Operation