Rane MPE MIDI Programmable Equalizer - Manual (Page 27)

27 Rane MPE Users Guide
Computing EQ Ramp Transition Time
In the figure below an MPE 14 is in transition
between two curves (the heavy lines). The Ramp is
set for 2 dB steps, resulting in intermediate curves 1-
5. To compute the total time required for the EQ
change you must add up the time required for each
step. The number of steps is determined from the
band (or overall level) that makes the largest change,
divided by the Ramp step size. In this example, the
16 kHz band makes the largest change of 12 dB. The
Ramp is set for 2 dB increments, requiring 12/2 = 6
steps to execute the EQ change.
Now we will calculate Tstep for each of the 6
Ramp steps (assume overall levels are 0dB for both
curves, and both channels are identical):
Tstep 1 = (26 x 200µs) + (0 x 900µs) + (4 x 70µs) + 600µs
= 5.94ms
Tstep 2 = (24 x 200µs) + (0 x 900µs) + (6 x 70µs) + 600µs
= 5.82ms
Tstep 3 = (18 x 200µs) + (0 x 900µs) + (12 x 70µs) + 600µs
= 5.04ms
Tstep 4 = (8 x 200µs) + (0 x 900µs) + (22 x 70µs) + 600µs
= 3.74ms
Tstep 5 = (6 x 200µs) + (0 x 900µs) + (24 x 70µs) + 600µs
= 3.48ms
Tstep 6 = (4 x 200µs) + (0 x 900µs) + (26 x 70µs) + 600µs
= 3.22ms
Total time = 5.94 + 5.82 + 5.04 + 3.74 +3.48 +3.22
= 27.24ms
Step 1: 26 bands (13 per channel) changed. No
overall levels changed. The 26 bands that
changed required 26 x 200µs. The stationary
bands and overall levels required 4 (2 bands + 2
overall levels) x 70µs. The software overhead
was 600µs. The grand total was 5.94ms.
Step 2: 24 bands changed, 4 didn’t. Two overall
levels didn’t change. This required (24 x 200µs)
+ (6 x 70µs) + 600µs = 5.82ms.
Steps 3-6 were derived similarly.
The time required for the EQ change in the above
figure is at least 27.24ms (the actual time is probably
1ms-5ms higher due to competing software tasks).
If the Ramp step size is changed to 1dB, a total of
12 steps is required. Since each intermediate step is
unique, simply doubling the time derived with 2dB
steps will not yield the correct answer. The addi-
tional 6 steps must be computed and added to the
above total.
So, unless you really really really really need to
determine the exact time a curve transition takes,
don’t bother. The quickest transition occurs when
one band changes in one ramp step. This takes
2.83ms. The longest transition occurs when all bands
change 27dB, and overall level changes 24dB, with
the Ramp set for 1dB steps (overall levels will be
constrained to 2dB steps since this is the smallest
overall level increment). This requires 191.7ms.
Therefore, all EQ changes will take anywhere from
about 3ms to 200ms to execute. The actual time will
be a little higher (typically 5%) due to competing
software tasks.
The time required for each step is calculated as
follows:
Tstep = (number of bands that change) x Tbc
+(number of overall levels that change) x Tlc
+ (number of bands and levels that don’t change) x Tnc
+ Toh
where:
Tnc = Time for EQ band or overall level to not change = 70µs
Tbc = Time for EQ band to change one step = 200µs
Tlc = Time for overall level to change one step = 900µs
Toh = Time required for overhead per step = 600µs