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Hands On – Lexicon PCM 70 (part 4)

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Powerful Performance

Since the PCM70’s primary function, to my mind at least, is as a digital
reverb unit, I think I should start at Program 3.0 – the first of the twenty-two
basic reverb Programs. The Programs in Row 3 of Figure 2 are designed to emulate
real concert halls, and they do a pretty good job too. As the manual states,
the reverb starts with a low initial density which builds up gradually over
time. As well as the reverberation itself, the Concert Hall programs also have
four early reflections, each of which can be independently adjusted for level
and timing. There is also a gate for stopping the reverb abruptly, an effect
which was especially popular on drum sounds at the time the PCM70 was introduced,
but sounds a bit naff now.


Stepping down to Row 4 (you press the down key to increment the number) we
find the Rich Chamber programs. I can’t improve on Lexicon’s description:
“The Rich Chamber programs produce an even, relatively dimensionless reverberation,
with little change in colour as the sound decays. The initial diffusion is similar
to the Concert Hall programs, but the sense of space and size is much less obvious.
This characteristic, along with the low colour in the decay tail make the Rich
Chamber programs especially useful on spoken voice, giving a noticeable increase
in loudness with very low colour.” This is actually a very helpful description
of the sound, not just an advertising copywriter’s message, which Lexicon
provide in their manual for all the Program families. When you understand the
designer’s intentions, it makes operation of the unit more rewarding (a
lot more rewarding than simply flicking through presets). The programs in Row
5 are plate simulations with a high initial diffusion and bright sound. Lexicon
recommend their use on percussion. Row 6 is dedicated to ‘creative’
Inverse Room programs. Many of the reverb programs have editable parameters
in common. Here is a selection which should indicate the power available in
the PCM70:

  • Attack sets the sharpness of the initial .response
  • Chorusing randomises delay times, adding richness to the sound.
  • Decay optimisation alters program characteristics according to input level
    to make the reverb decay more natural. This can be set On or Off. The off
    position is used if clicks are noticed.

  • Definition controls the build up of echoes during the latter part of the
    decay.

  • Diffusion controls the density of echoes.
  • Delay master changes simultaneously the delay times of all the early reflections.
  • Duration determines the length of time before cut off in the Inverse Room
    programs.

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  • Gate sets the time delay before reverb is stopped.
  • HC (High frequency cut off) applies a 6dB/octave filter at a selectable
    frequency.

  • Lo slope (Low frequency slope) determines the shape of the reverb envelope
    at low frequencies in the Inverse Room programs.

  • MD slope (Mid frequency slope). Same as the above but for mid frequencies.
  • L RFL DB (Left early reflection levels). The level of each early reflection
    in the left channel can be adjusted.

  • R RFL DB (Right early reflection levels). Similar to the above.
  • L RFL MS (Left early reflection delay times). The delay time of each early
    reflection can be adjusted.

  • R RFL MS (Right early reflection delay times). Similar to the above.
  • LVL MST (Level master) allows simultaneous changes in the early reflection
    levels without altering the relationship between individual reflections.

  • Mix controls the ratio of dry and processed signal.
  • PDelay (Pre delay) sets the time between the input signal and the onset
    of reverberation.

  • Reverb time. I think you know this already.
  • RT HC (Reverberation time high frequency cut off) sets the frequency above
    which sounds decay at a progressively faster rate.

  • RT Low adjusts the low frequency reverberation time.
  • RT Mid. Similar to the above.
  • RTL stop sets a separate reverberation time for low frequency signals when
    input has ceased.

  • RTM stop. Similar to the above but for mid frequencies.
  • Size sets the room size.
  • Xover (Crossover frequency) sets the frequency at which the transition from
    low frequency reverb time to mid frequency reverb time takes place.

As you can see, there is a good range of parameters available, but not I think
too many to put the average user off editing the original programs. The one
drawback is that the display is quite small and some of the parameter names
have had to be abbreviated beyond the point where people can be expected to
work out their meaning – but you have to remember that classic effects units
have their failings, just as classic cars leak oil.


The other effects have a whole new set of adjustable parameters, far too many
for me to go into here, but I must mention the PCM70’s party trick. Every
engineer will want to use it at least once and I recently placed it, suitably
tailored, on the opening of the CD ‘The Killing Tide’ by Sol Invictus.
The effect is known as Resonant Chords.

David Mellor

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David Mellor