| manisandher wrote:|
|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, I am not sure what Mr. Johnson meant by saying that Pacific’s output “can energize loudspeakers to reasonable volume”. It sound ridicules statement coming from him. Anyhow, about the second question. Since it uses ladder-resistor architecture then it is multibit, which is good. Multibit at 4x sampling rate would require much less alias removed, if any. This is what I would like to try – to run 4X DAC with no post-conversion filter of any kind – with multibit architecture it is possible in case my electronics can handle HF. Do not forget the I power my system with Melquiadeses that have low pass filters built-in (bias resistor in grid against the Miller capacitance of the driver tube).
The Pacific’s however do not have the output as a normal multibit. If you look at the Pacific’s output at minus 90-100dB then you will not see the individual sticks as it would be with other pure Multibits (Lavry 924). The individual sticks will be blurred and I think that here is where the Pacific’s dithering in work.
I understand that you like the sound of your Pacific but you do not know it sound as you use just D/A section. The Pacific A/D section is much more interesting then it’s D/A section. You need to record with Pacific to get a true understanding what kind machine it is. In addition as I understand Pacific has an ability to write dither during recording and then to inject in D/A the same dither in the opposite polarity – this is superbly cool idea. Anyhow, start to record and you will love this processor even more.Rgs, Romy the Cat
"I wish I could score everything for horns." - Richard Wagner. "Our writing equipment takes part in the forming of our thoughts." - Friedrich Nietzsche