Reference Monitors User Handbook
61
SERIAL INTERFACE
COMMANDS & RESPONSES
SERIAL INTERF
A
CE C
OMMANDS & RESPONSES
5
User-Variable EQ Parameter Format
The DSP coefficients 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 coefficients M1, M2 and M3 can be calculated. They differ 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 coefficients 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 five-byte string (five hex character pairs) is sent with the coefficient
bytes sent MSB first. The upper nibble of the MSB should be all zeros.
Coefficient updates will be applied instantly.