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In the Forum: Didital Things
In the Thread: Pacific Microsonics Model 2

Post Subject: Some interesting informationPosted by manisandher on: 5/27/2010

I asked Dave Peck of Avid (formerly Euphonix) a few questions regarding the Model Two (otherwise known as the PMI). The responses he received from Keith Johnson (one of the original designers of the PMI, head of Reference Recordings and chief design engineer at Spectral Audio) are shown below:

1. What is the max. RMS output voltage of the Model Two?
The PMI converters produce a specified maximum output of +24 dBu from 0 dB FS modulation, which translates to 12.28 volts RMS. or 34.7 Volts peak to peak as seen on a scope. I believe the output impedance is less than 20 ohms so the machines produce roughly 11.5 Volts into a 600 ohm load. The driving amplifier is capable of at least twice this output so it can accommodate DAC outputs with ringing and other filter artifacts that might be introduced or chosen for sonic reasons. It can energize loudspeakers to reasonable volume.

2. Having used the Model Two for a year or so now, I am convinced that it is non-oversampling at 176.4/192KHz rates. Could you confirm this either way?
Up conversion is not used at 176.4 kHz and 192 kHz sample rates. Instead, A passive analog filter with group delay correction removes alias products so that all 24 bits of information are captured from each sample by the ADC process. Conversion is made with ladder-pipeline architectures and analog added - DSP subtracted dithering, a first of its kind that is still used for instrumentation. Unlike sigma-delta methods, jitter sensitivity is low and accuracy does not degrade at high program levels.

Mani.

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