> But again re reading your first post I think the laptop is still
> reading its disk but there are newly introduced SPDIF and upsampleing
> steps in the data path.
I would suspect that in fact it's not using the disk at all (that is, on the laptop that's "bridging" the RME Babyface USB input to the Phasure NOS-1a USB output via the built-in Windows 7 playthrough capability).
Remember, there are actually **two** computers in the system I'm describing. The computer that has the music files and the music player is the one I usually use for audio playback -- an HP minitower (quad-core i7, with Windows 7 64-bit).
The (current) architecture of the whole system is not unlike that of a dual-PC system using HQPlayer on a PC connected over a LAN to HQPlayer's NAA (Network Audio Adapter) on a second PC that's actually performing the job of feeding the audio to a USB DAC (or the similar arrangement using JRiver Media Center on one PC connected over a LAN to a second PC running Jplay and feeding audio to a USB DAC). Except that instead of using Ethernet to connect the "control PC" to the "audio PC", I'm just sending the data via S/PDIF (or ADAT). And it's the RME Babyface USB interface that's getting the ADAT (or S/PDIF) -- the laptop only sees USB data coming in and going out; it's certainly not doing any sample-rate conversion, and it's not reading or processing audio files.
I've actually got a sort of "optical bus" running around the house. The source PC (running foobar2000, usually) is connected over Firewire to an RME Fireface 400 that's clocked by an Antelope Isochrone. The Fireface sends optical output to the first audio-system "station" on the bus -- the "station" is either an Apogee Big Ben or an RME ADI-192DD that takes in the optical and then passes it along to the next "station" (the optical links are up to 50' Hosa glass cables). The Big Ben or ADI-192DD can then feed a DAC, or a signal processor (like the Purcell), etc., etc.
I also installed that "Fidelizer 6.5" program on the laptop (the Toshiba laptop's also a quad-core i7 machine running Windows 7 64-bit; both machines have plenty of memory -- 6 or 8 GB, I can't remember exactly), and put Fidelizer into "Extremist" mode, so the laptop should be pretty quiet --
I don't think Windows would have any need to page to the hard drive, and I can't see why it would be putting any audio on the hard drive -- I would think the buffering would all be done in memory.
Oh, speaking of the Purcell -- I just noticed that in fact when you're doing upsampling from 44.1k to either 176.4k or 192k, with 24-bit output word length, both dither and noise shaping are automatically turned off, and cannot be turned on, at least with the firmware in the unit I'm using (these things go through multiple generations). I hadn't noticed this before (I'm used to using the Purcell in other modes, such as doing 44.1k->96k and then
reducing output word length to 18 bits to feed an Audio Note NOS DAC capable of taking 96kHz). So much for the theory in that IAR article about noise shaping!
And as far as playback glitches are concerned -- they do happen from time to time (every 15 minutes or so maybe?) and are quite audible, even with Windows 7 playthrough and Fidelizer. They sound like buffer underruns to me -- the audio drops out, comes back, drops out for about a second or two altogther, then goes on for a long while before the next one. There were a lot more of them when I was using Audacity to do the playthrough (and they were different -- raspberry-sounding things: brrrrrr for a second or so. A buffer overflow in that case?). So again, I'm not really recommending this to anybody.