suggest is much more manageable than the usual ‘point nought five per cent’ (-66dB) and
should become established practice; as is tending to happen with distortion figures.
However, for the less daring, a digital percentage conversion is also displayed! A signal
level of -20 to +10dB is recommended for flutter measurement, but the unit does in fact
constantly monitor the signal level and frequency and display BAD TONE if either goes
out of limits. W&F can only be measured on the left channel which is automatically
selected. The measurement complies with IEC386, DIN45507 and BS4847-1972.
Although the ideal might be to use a perfect test tape for flutter measurement, it is usually
more practical to make record-replay measurements, a 3.15kHz (0dBu) tone being first
recorded on the same machine. The level of W&F on tape recorded on a modern
domestic or professional machine is often as good as the W&F present on most test tapes
A point to watch for is cancellation of slow rhythmical variations if they happen to
synchronise between record and replay. Stopping and starting the tape a few times should
show up such effects. Simultaneous record and replay should not be attempted as this
may also cause cancellation. Listening to unweighted flutter components can give an
interesting indication of ‘scrape flutter’.
Flutter measurement
W&F options 6 and 7 provide weighted and unweighted wow & flutter using an rms
rectifier, while the other W&F options are used for miscellaneous measurements
(described below).
Fig. 2.13 Wow & Flutter Fig. 2.14 Speed Measurement
2.15 Speed Measurement
Tape speed can be measured using a speed reference tape. Wow and flutter options 11 to
13 (
to ) provide speed measurement using 3150Hz, 3125Hz or
3kHz reference tones respectively (fig. 2.14). 3150Hz is the most common frequency, but
3125Hz must be used if the speed tape was recorded using the LA101 which cannot
generate 3150Hz (see section 2.2). The speed error is displayed as a percentage, accurate
to ±0.04%, and a
BAD TONE message is displayed if the frequency is out of range. The
level bar graph and numerical dB reading indicate the measured level (using an rms
rectifier). Unfortunately, it is not possible to measure speed at the same time as
measuring W&F, but note that
will quickly toggle between option 1 and option 11.
26
2. Manual Operation
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