Andrew, if you're still watching this thread I thought of something that might be nice for people to see.
Since you have different DSP routines for the different speakers, can you make a "null" routine? One that just passes the input to the output?
Load that, and post a sweep showing how transparent the ADC-DSP-DAC signal chain is in the audible frequency range.
As for a direct digital input, the above should show how unnecessary it is, but also it would be difficult to make use of it. First you'd need something doing digital volume control, unless you like ALL REFERENCE LEVELS ALL THE TIME. Plus with HDMI and HDCP it's difficult to get a digital output for most media these days.
Hi Chris (and Charles65),
I can happily (and will do so later today) post some graphs of our DSP box in straight "pass-thru" mode. Honestly, there will be nothing to see in the amplitude response curve until you approach the Nyquist Frequency (f_s/2) where there will be a steep roll-off. Distortion and noise are also of a magnitude below that of most amplifier stages.
I do understand the concern anytime something is inserted within the analogue signal path, and the timing of your posts is excellent as we are going to be embarking on a controlled test in late August that will be of interest to many of you. Basically will are going to setup a reference front end system comprising a calibrated open reel deck on which we will be playing 2 track mix-down master tapes. For many this is considered the absolute ultimate in purely analogue source material. The signal from this deck will pass directly to a Bryston pre-amplifier, or through our DSP box running in "pass-thru" mode. Because our DSP is unity gain no level matching will be required, and all switching is performed with high quality, silver contact signal relays. Listeners will be able to switch between the two signals at will and can listen via loudspeakers, headphones, or their own supplied headphone systems. We will have a Bryston headphone amplifier for headphone listening. Ian will supply the specific details as we nail down firm dates and have procured some master tapes, but this session will run for a number of weeks and be open to ANYONE that would like to make the trip here to participate.
The question of digital inputs, as Chris correctly points out, is fraught with problems and only removes the ADC component from the equation. Simply trying to determine all of the required inputs and format standards results in a device that would be riddled with inputs and additional cost, not to mention ever-changing formats and HDCP requirements. In that sense it makes much more sense for us to stay within the analogue chain.
