of each bank press . While holding , press to to run sequence 6 to 10
respectively. For example, to run sequence 27: Press
to enter sequence mode; press
until sequence titles 21-25 are displayed; press to run sequence 27 (note that
represents the digit 6, represents 7 etc).
When a bank has been selected, it becomes the current bank and will be used next time a
sequence is run (ie after running sequence 27, pressing
will run sequence 21).
After the LA101 is turned on or reset (by tapping the
key), the current bank is
set from configuration B.
New users should first gain experience with the default Lindos sequences in Bank 0
before using sequences in other banks or editing sequences.
The 10 Lindos default sequences vary mainly in the levels at which each test is carried out
relative to test level, and the levels used are the result of careful analysis of various codes
of practice and specifications issued by the BBC, IBA, ITC, British Telecom, IEC, EBU
and CCITT. The use of +8dB for distortion tests is fairly standard, except for line testing
where +9dB is used. A level of -10dB has been chosen for the sweep in sequence 11, in
line with the BBC requirement for testing tape machines, and the IBA code of practice. A
sweep (segment Q) at -12dB is available in line with CCITT/EBU recommendation O.33
for line testing. Sequence 12 incorporates a frequency sweep at -10dB which gives a
printout to British Telecom specification EPS84 and also incorporates a ‘rest’ period
between the two high level distortion tests to minimise the risk of overloading FDM and
satellite systems. Sequence 13 uses a sweep at -20dB as is common in testing cassette
machines to avoid high frequency tape saturation.
Testing loudspeakers O.33 sequence
Sequence 14 is useful for testing loudspeakers and other devices where crosstalk and
noise are irrelevant. It is recommended that a working level of say 90dB SPL be adopted
for loudspeaker testing, while the distortion test will be found quite meaningful at +98dB
SPL.
Sequences 15 and 20 provide repeating frequency sweeps which can be used to see the
effect of making changes to a piece of equipment which affect its frequency response
(perhaps adjusting tape bias for example). The sweep repeats until stopped by pressing
on the LA101 (press and hold on the LA102 to stop it updating). Sequence
15 uses a fast 1½s sweep while sequence 20 provides a slower 5s sweep which will be
more suitable when testing steep filters. The LA102 plots the frequency response as it is
measured and the usual graph keys on the LA102 operate to move the cursor, zoom in or
switch channels etc (see section 3.3). These keys operate during sweep measurement, but
not during FSK input (which only lasts a small fraction of the repeat cycle anyway) and
the display shows ‘SEQ’ or ‘FSK’ to indicate the mode. Do not worry that scrolling and
cursor movement sometimes causes graph plotting to fall behind fast sweep input, as the
sweep input is independently timed and not affected by graph plotting or key presses.
48
3. Sequence Testing
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