Manual

Table Of Contents
Reference Monitors User Handbook
53
SERIAL INTERFACE
COMMANDS & RESPONSES
SERIAL INTERFACE COMMANDS & RESPONSES
4
User-Variable EQ Parameter Format
The DSP coecients for the user-variable EQ need to be pre-calculated before being sent
to the Reference Monitor.
Each band of EQ is a parametric equaliser with the following parameters:
F = centre frequency in Hz,
BW = bandwidth in octaves
G = height of peak/trough at centre frequency (linear, so 6dB=2.0, 12dB=4.0, etc)
First, the following intermediate values should be calculated:
R = ((2^BW)-1)/(2^(BW/2))
K = tan(pi*F/48000)
A = G – 1
From these, the three coecients M1, M2 and M3 can be calculated. They dier according
to whether boost or cut is required.
If boost is required:
M1 = (A*R*K)/(1+(R*K)+(K^2))
M2 = (4*(K^2))/(1+(R*K)+(K^2))
M3 = (1-(R*K)+(K^2))/(1+(R*K)+(K^2))
If cut is required:
M1 = -(A*R*K)/(1+(G*R*K)+(K^2))
M2 = (4*(K^2))/(1+(G*R*K)+(K^2))
M3 = (1-(G*R*K)+(K^2))/(1+(G*R*K)+(K^2))
The resulting three coecients should then be converted to S3.24 format, i.e. one sign
bit, three integer bits and 24 fractional bits. It is in this format that they are sent to the
Reference Monitor. A ve-byte string (ve hex character pairs) is sent with the coecient
bytes sent MSB rst. The upper nibble of the MSB should be all zeros.
Coecient updates will be applied instantly.