Roland GS-10 User Manual download pdf (Page 2)

1 Invalid equalizer responses

The GS-10’s frequency responses for the Low EQ and High EQ parameters of the Equalizer and

Stereo Equalizer effects are wrong for values below 0 dB:

The frequency response plots below (generated by a third-party frequency sweep program) show

the GS-10’s actual responses for several values of the Low EQ parameter (where the Lo-Mid, Lo-

High, High EQ and Level parameters are kept at 0 dB). The table (on the right) picks out a few

relevant values. (Note: these values can even be estimated if one sends a 20 Hz signal to the GS-

10 and then checks the values produced by the GS-10’s own Meter.)

Low EQ parameter Actual response at 20 Hz

+20 dB +20.0 dB

+15 dB +15.0 dB

+10 dB +10.0 dB

+5 dB +5.0 dB

0 dB 0.0 dB

!5 dB !2.3 dB

!10 dB !5.5 dB

!15 dB !10.7 dB

!20 dB !24.0 dB

Thus, for most values below 0 dB the actual cuts are substantially less than what they

should be, but for !20 dB the cut is deeper than it should be!

The cause of this weird behavior must be a confusion between linear and logarithmic scales

in the GS-10’s algorithms for the Low EQ parameter: I have found that the GS-10’s actual

responses for the Low EQ values below 0 dB can be approximated by means of a formula like

20 ×

log (1 + 0.04705 × x), where x stands for the Low EQ value.

The High EQ parameter’s behavior is wrong in roughly the same way as described above

for the Low EQ parameter.

Since it’s just a matter of changing a few fixed parameter values in rather simple low- and

high-frequency shelving filter algorithms, it should be relatively easy to fix this problem in the

GS-10. (Obviously, current users would have to be warned that their patches might start to sound

different if their GS-10s are upgraded, but personally I would definitely prefer the upgrade.)

Low EQ

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Roland GS-10 User Manual Page 2