My ultimate VTPO goal, was to attempt to create an illusion of a modern studio WurliTzer theatre pipe organ. Amongst my target installations were the George Wright Pasadena and Hollywood 'Philharmonic' studio recording pipe organs and the Little River Studio WurliTzer http://www.nyparamountwurlitzer.com/lrs.html. My suggestions are therefore made with those dryer acoustic environments in mind which require the highest achievable tonal integrity as the samples can't hide behind a veil of reverberation.

Which audiocard to use?

As I value sound quality, more highly than how many channels a particular card has, after experimenting with Egosys, M-Audio, Terratec, and MOTU, I found that the best compromise (and all systems are a compromise) are the Echo Audiofire range. I use three Echo Audiofire 12 (AF12) in my VTPO.

The review of the AF12 in Sound on Sound magazine clearly states why the AF12 sounds better than its competition:

"These particular converters use IIR (Infinite Impulse Response) filters instead of the more usual FIR (Finite Impulse Response) designs adopted by most competitors like AKM. Much research has been carried out to determine why many people hear an improvement in digital audio quality at 96kHz and higher sample rates compared with 44.1kHz, and many experts now seem to agree that it's not the extended frequency response that provides the audible improvements, but the gentler high-end filtering, resulting in better impulse response with less 'time smear' and cleaner transients."

The full review is here: http://www.soundonsound.com/sos/oct05/articles/echoaudiofire.htm

However, be sure that you do not purchase the earlier AF12 units as the unattenuated ultrasonic noise from the IIR filters can wreak havoc with some amplifiers. These earlier spec AF12s can be identified by the orientation of their firewire sockets (current spec AF12s firewire connectors are upside down). 

With any multi-channel audio you must be scrupulous with your grounding. If you plan on deploying two, or more AF12s, to follow Echo's advice in the AF12 manual about master/slave daisy chaining multiple AF12s can, in my experience, cause too many ground returns. Unlike true high end sound cards, mid level soundcards like the Audiofire range, the BNC connector ground is not galvanically isolated from AC, or audio ground (indeed they are tied together on an AF12). I have found that it is better not to use a RG59 word clock cable between each AF12 and permit each unit to look after itself using its own internal clock. Even when operating like this, I terminate the output of each word clock with a BNC terminator (basically a BNC connector with a 75ohm resistor installed from centre to ground) to ensure maximum stability from the AF12 word clocks.

The best advice that I have found to date about word clock termination is from the Presonus site:

The multi channel grounding advice that I have found anywhere is this article: http://www.soundonsound.com/sos/nov02/articles/studioinstallation1102.asp. Pay particular attention to what the author suggests for balanced connections. As a direct consequence of this article, I recabled, and re-equipped my VTPO so that I would not have any grounds running from an AF12 to an amplifier, and the difference was staggering. Well worth the several hours work. In addition to the electronic glassiness that too many ground lines can add to a multi channel audio installation purely from too many ground loops (not to be confused with hum), each ground line can potentially act as an RF antenna and feed that back into all other channels making for one very ugly outcome that is a long way removed from any pipe illusion.

If you did not wish to address the word clock issues, and you required 24 channels, then with the MOTU 24 I/O you could avoid having to do anything with a word clock!  However, the MOTU's power supply is rudimentary in design when compared to the Echo AF12 (I had two power supplies fail), and the sound quality is not in the same league as the AF12. However, there is a company who modifies MOTU products to improve their sound quality:  http://www.blacklionaudio.com/Modifications/MOTU+Audio+Interfaces. I can't comment on whether the outcome matches, or exceeds the audio quality of the AF12. However, Jim Gallops said that he was sending one of his units to BLA, and he would let me know the outcome.

More to come.....................

© Ian McLean