Hugh Robjohns wrote:
Martin Walker wrote:A quick check on its frequency response using the PluginDoctor utility (Dirac Pulse test signal) suggests that this rises significantly above 1kHz.
Yes, that's quite common.
My AP test system defaults to an input impedance of 200k Ohms, and that's so high as to be effectively an open-circuit load for a lot of transformer outputs. The result is almost always a high resonant peak around 50kHz or so.
Load the output with 10k Ohms and the response usually flattens out... and often loading with 600 Ohms introduces a gentle HF roll-off.
So when you come to experiment with your own taming Zobel network, make sure you also load the output to match whatever it normally plugs into, otherwise you might find you over-correct!
Ironically I'm already doing that, testing the DI box by inserting it between my Fireface UC phones output and one of the mic inputs, which is quoted as having an input impedance of 2k, so I was fully expecting the result to be suitably loaded.
Low-end response of the Fireface UC mic inputs @44.1kHz is quoted as a very useful -0.5dB @18Hz, while the phones output is an excellent -0.1dB at 1Hz and 20.4kHz, with an output impedance of just 30 ohms.
However, this is the response I've initially measured :shocked:
I suspect the software is having a minor fit testing hardware, as the top end of this curve doesn't shift sideways on screen if I alter the sampling rate as it does when testing software plug-ins.
Anyway, out with my boxes of resistors and tiny capacitors ;)