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[jessel]

I have all my music ripped onto my computer in APE files, and I stream out of a Creative USB sound card SPDIF into a Mark Levinson DAC (through a seperate jitter suppressor of course).  It all sounds great, but what I really want to do is use my computer as a crossover in the digital domain, and then bi-amp or tri-amp my system.  Does anyone know of a sound card system which can divide a source into different freuencies and output multiple digital signals?  I do not want to use the DAC's on sound cards, as they are generally inferior to audiophile DACS, hence I want the output digital.  I do not mind buying more than one card if that is a solution, but I have never seen a card which was configurable in that way.  It seems like such a logical solution to a very difficult problem, after all dividing the signal while it is still digital eliminates all the problems of passive and active crossovers, but no one seems to have done it.  Any ideas?

[jgreen]

Well, they laughed at the Wright Brothers, too.  FWIW, I would sure like to hear how this turns out.

I think what you want is a studio mixer.  Go to Musician's Friend.com, and other such sites to view the possibilities.  It looks like you need 5k-10k just to get started.  And I'm not sure that the sound would benefit.  And you'd probably have to triple up on the Mark L.   And next year the whole package might be available in a $500 consumer card, who knows.  But best of luck, and write back with your results.

[Myron]

There are loudspeaker design software packages that allow you to emulate crossovers in the digital domain.  One example is Soundeasy (http://www.interdomain.net.au/~bodzio/) which I've used in the past.  To keep things digital you'll need a sound card that has multiple SPDIF output channels.  All the channels need to be on one card to work with Soundeasy.  I don't know if such a card exists. 

I know of two digital crossovers, the Behringer DCX2496 (http://www.behringer.com/DCX2496/index.cfm?lang=ENG) and one from DEQX (http://www.deqx.com/), but they only has analog outputs.

That said there are still two problems to overcome.  The first is that the digital filters need to have many taps to work well at low frequencies.  I'm not sure how many is really enough, but this discussion alone could fill volumes.  The second problem is finding a good way to implement a volume control for all the channels you'll have, six is you want to tri-amp a two channel system.  If you want to do surround you'll need more, of course.  Doing volume control in the digital domain has its own set of problems.  A six channel analog control is available in many AV controllers, but you may not find their quality acceptable.

I'd like to do the same thing some day, but for now it's not practical.  I built an analog active crossover for my system.

[jessel]

I have read about the Behringer, and almost bought one to give it a try.  But in the end I figured it probably would not have the sound I wanted.  Once you get used to a real Hifi DAC like the ML, it is impossible to go back to a mid-fi DAC, which has so much less tonality and spacial imaging.  Unfortunalty, the the Behringer is not the sort of thing that Stereophile tends to review.  I find it so strange that the hi-fi world is still debating about ripping music at all, and fetishising the CD.  Once I have ripped my CD, I am confident I have every bit of information from it stored on my computer.  Feeding a DAC is just a matter of having the info (which a computer does better than any transport) and making sure the timing is good (which a good sound card augmented with a jitter suppressor box does fine).  It would be a lot more interesting to see an artice on upgraded sound cards and multiple amps than another $5000 pre-amp. 

[jgreen]

Have a look at the RME website, have a look at the Creamware.  I know the RME has a version that will output synched spdif, if you are able to separate the signals in software.  You must satisfy yourself that the issue of  word clock sync in mulitple spdif optical CONVERSIONS is not defeating the benefit of tri-amping.
Audiophile companies do in fact fetish on cd drives.  The goal is revenue-enhancement, after all.

[Myron]

I have read about the Behringer, and almost bought one to give it a try.  But in the end I figured it probably would not have the sound I wanted.  Once you get used to a real Hifi DAC like the ML, it is impossible to go back to a mid-fi DAC, which has so much less tonality and spacial imaging.  Unfortunalty, the the Behringer is not the sort of thing that Stereophile tends to review.  I find it so strange that the hi-fi world is still debating about ripping music at all, and fetishising the CD.  Once I have ripped my CD, I am confident I have every bit of information from it stored on my computer.  Feeding a DAC is just a matter of having the info (which a computer does better than any transport) and making sure the timing is good (which a good sound card augmented with a jitter suppressor box does fine).  It would be a lot more interesting to see an artice on upgraded sound cards and multiple amps than another $5000 pre-amp. 

I agree...

Perhaps some day we'll be able to buy a preamp with built-in digital crossover functionality.

[patricklang]

I would say that at this point in time - its not worth it.  I did this as a project using BruteFIR with an M-Audio Revolution 7.1.  We calculated the ideal curve (phase and amplitude) for our crossover using Matlab based off of our driver measurements in an anechoic chamber.  With several thousand taps, we couldn't hear any imperfections due to the crossover.  What we could hear vs the original analog crossover - more noise.  Granted, this wasn't an audiophile card, we were doing this as a class project, but it wasn't worth it to use it in the end.

Another thing - in digital audio, your quality is limited by the number of bits going in.  Splitting them out in the digital domain isn't going to magically make more bits appear.

As far as other solutions out there:
TACT audio has some stuff well-known for live sound / theater.  The goals are a little different there, you need to be able to adjust your system, both frequencies, amplitudes, and delays, and these were designed to provide that flexibility.  They have also introduced this into the home market as "room correction" products.  I've never used any of it personally.

Behringer is known for cheap knockoffs, although some people like the DBX mentioned here.

I'd stay with a good DAC and use passive crossovers designed by a good EE.  You may gain something from a bass management system from one of the usual audiophile companies if you have integrated a sub.

[avpman]

Jessel,

I'm curious about your current setup. Would you mind a couple of questions?

1) What brand/model of jitter reduction device are you using?
2) In your opinion, is there a better audio card with spdif output than the one you're currently using (Creative/USB)?

FYI - I currently have two processors (AVP-II processor, Lexicon MC-1). I'm getting rid of one of them. The AVp seems better for Movies/DVD and the Lexicon for music.

Thanks in advance!
Jim

[avpman]

Thanks for the info. I like the USB solution since I was wondering how I'd be able to run fiber from the main PC to the home theater equipment. If I use the USB device will the cd's native 44.1 sample rate be preserved and not upsampled by the device?

[Nolonemo]

Please excuse a noob-type question here, but I'm running digital out from my Creative Audigy to my HT receiver's digital in via a 50' coax run, and it seems to be working fine, though I'm by no means an audiophile (and no longer have the ears for it if I wanted to be).  Why would usb using repeaters be superior to this, wouldn't the repeaters introduce some noise, or is the digital signal immune from that?  Or is the 50' coax run degrading the digital signal and I'm not aware of it?

And as long as I have knowledgeable people here, what's the deal with the coax to optical (or vice versa) converters I've seen, do they work OK, or do they degrade the sound somehow?

Thanks!

[jgreen]

Until "kowledgable people" reply, I'll give you an account of my personal experience, although it's OT from jessel's original question about digital crossovers.

I ran a ~60 foot digi coax from my workstation and found it superior to running analog RCA the same distance.  My theory is this:  that digi coax PCM is a square wave, on- or off-state signal, and as long as the recieving decoder can tell the difference between on or off, there should be no audible diminution from (digital) signal diminution.  This is opposed to analog, wherein high frequency fades over distance at a greater ratio to low freq, resulting in bass rising over longer distances (~50ft). 

Optical should be avoided.  First, the signal runs reliably about 10ft max using consumer encoders.   Secondly, you introduce an additional coding/decoding step into the process.  I tried the optical/copper dconverter you mentioned, and it seemed okay for converting, but the signal fell off very quickly.  So use it if you must wnen you've run out of copper I/O in your preamp, but there's no reason to switch from copper.

[MAPgeekdad]

Hi Camper,

Me again, with questions on your setup (and for everyone else to chime in please). 

I assume that in all this you (and others) are wanting to feed a digital signal from a single source PC directly into one or more distributed audio setups in different rooms. 

As opposed to having a networked PC in multiple rooms running say JRiver that reads the FLAC off your network library? 

Do you find this any less quality doing such running over a network? Of course gonig into an external DAC after soundcard S/PDIF out.

Thanks!

[damianhl]

Jessel,

It is great joy to learn that another person shares exactly the same idea like myself.  Your idea of getting your PC to do digital crossover-over came across my mind in about 2-3 years ago.  It sparked an in-depth research, which I have sinced embarked in search of an ideal full-digital audio setup.

To be fair, the processing power of PC and sonic quality of audio cards have since improved significantly.  However, at the time of my quest, the main challenge in addition to finding a quality hardware/soundcard that supports multi-channel digital I/O (w/ surround sound support), is to find the appropriate driver and software combination to achieve the goal of "realtime" digital crossover, and still offer Hi-End sonic quality.

The search for a possible solution, based on PC soundcard, did not yield much success.  But in the process of discovery, I learn that in addition to achieving the crossover task itself, there are also other challenges which this potential solution must offer, before it can be considered as offering a complete solution.  Examples are a wide-range of cross-over slope for selection, the offering of compensation for the phase lags introduced by various crossover (slope) designs, speaker driver calibration and alignment in both the frequency and time domains, room accoustic compensation...etc.

After having done more research, eventually, the solution to the above requirements and challenges all seem to gravitate towards one unique product --- The DEQX PDC 2.6p.  A crossover unit, which runs on 2 high-speed SHARC DSPs and offers a software based solution to address all the above challenges like no other product I have experienced in the market.  Another selling point with the DEQX unit is that it is the one of the handful of crossover units which operates completely in the digital domain and is targeted towards addressing the needs from both the Recording Studio and Hi-End audio sectors.  The only other similar product is the Accuphase DG38+DF35.

You'll be glad to know that with the Digital Output (supporting both RCA SPDIF and XLR AES/EBU) Add-In card installed, the DEQX will support full-digital I/O and function as a crossover unit in the digital domain at upto 96kHz/24-bit.

The best part of the DEQX unit is that it allows you to connect the unit (via USB) to your PC, perform measurements using a calibration mic, compute the software-based filters on your PC for both the driver's frequency and time-domain corrections, then load these setting back to the unit for operation.  With the latest release of the v2.2 software that supports 96kHz, you can even opt to get the upgraded version mic --- Earthworks M50, that will support 3-50,000Hz calibration, and create calibration profiles for your sound system that will cater for SACD playback (assuming you have got your super-tweeter setup).

Volume control in the digital domain has always been a concern to me.  The result from bit-truncation at low volume setting, which eventually lead to loss in bit-resolution is simply not acceptable to me.  So despite the PDC2.6p can double as a digital pre-amp, I have opted for a different solution.

Since my goal is to achieve a full-digital setup, which also caters for my AV needs, the solution again mandates for a (AV) pre-amp that will offer Hi-End sonic quality, yet supports full digital I/O, and MUST offer a digital volume control which does not degrade as volume setting drops.  Sad to say that there aren't that many AV-amp that will meet this criteria.  However, with persistence, I eventually found the ideal solution from the Goldmund SR-8.

The Goldmund SR-8 is quite a unique piece of audio equipment.  In a nutshell, it is a digital pre-amp that also offers a software-based solution to cater for AV needs.  It basically shares identical DSP hardware platform with the Goldmund Mimesis 24 and 30, and the only limitation is that it ONLY supports upto 8 digital channel output.  The SR-8/Mimesis 24/Mimesis 30 architecture is similar to those of the DEQX 2.6p, and is based on 3 Hi-speed SHARC DSPs, and offers a software-based solution that is capable of evolving to cater for any new and upcoming digital surround standards.  All analogue and digital signals are converted into 96kHz/24-bit for processing and output.  Once again, you'll be amazed by the SR-8 flexibility to configure its output profile via the PC-based software.  Possibility is almost endless.  And interestingly enough, you can also update the SR-8 firmware to SR-8F and use the unit as a digital crossover unit.  Although it only supports upto -24db/oct, and it is not as versatile as the DEQX when used as a crossover unit, as the PDC2.6p supports -300db/oct.

With this many digital output, the challenge will also be to find enough DACs to decode these many digital audio channels, yet providing the anticipated Hi-End sonic performance at a reasonable price.  I am happy to report that the APOGEE DA16x will meet this requirement easily.  And to meet my extreme demands on sonic quality, the critical mid-range will be run by the dCS 974 + 955 at a later stage once the "dust settles".

I have been running the Goldmund SR-8, with the DEQX 2.6p and the APOGEE DA16x for a few months now.  The sonic performance is like nothing I have experienced, simply breath taking...for once I am experiencing music purity at "ground zero".  My JBL Project K2 speakers + UT045 Beryillum super-tweeters have gained new life and found a new purpose to serve (it is amazing to witness how extended they can be driven in an active quad-amp setup).

Of course, with this many equipments all operating in the digital domain, new challenges may be introduced.  Occationally, I get a few pops-n-clicks as a results of slight differences in reference clocks.  So I am in the process of sourcing the APOGEE BIGBEN to generate a reference clock signal, to be fed into each digital equipment as the Word-Sync input.

Shall let you know more about the result of my conquest soon.

 

Cheers,
Damian.

[goatherder]

Fascinating solution.

Are you the Audiophile who was running the Sony HD5 with the Sony Qualia 010 by the way?

[damianhl]

This is an update to my first post, regarding the implementation of a full-digital audio setup that caters for AV-needs.

In keeping with the setup principles pertaining to the Goldmund Universal Preamplifier, the digital-to-analogue conversion is to take place at a close proximity to the dedicated amplifier and speaker.  For the side/rear surround channels, this implies running dedicated DAC with monoblock amp(s) positioned next to the surround speakers.

I have considered various options to transmit the digital audio signals:
(1)   Optical TOS-link: Not ideal, as it may require a repeater every 5m or so, and will only support up to 48kHz/24-bit.
(2)   Coaxial SPDIF: Workable, but will require running 4 thick and inflexible cables to the rear.  Only supports up to 96kHz/24-bit.
(3)   Balanced AES/EBU:  When this is implemented using normal balanced cable, the challenge and constraints faced are similar to option(2).
(4)   Cat 7 Network cable carrying double AES/EBU: This option requires me to improvise in building two pairs of converters (Balanced to Cat7). 

Having evaluated each option, I have eventually decided to go with option (4).
Given that the Cat7 cable is rated at 600MHz and in most implementation is good for 750MHz, this should support quality transmission of digital audio signal of all sampling rate, which current Hi-End DAC will support.

In my current setup, I have decided to go with double AES, with each pair running two channels of 192kHz/24-bit digital signal for the side and rear surround speakers.  Two Cat7 will be required for this setup, one running down the left side (for side-left and rear-left surround), the other running down the right side (for side-right and rear-right surround).

It should be noted that I have reconfigured the digital output of the Goldmund SR8 so that the side and rear surround is regrouped to support the above connection schema.

Each pair of the converter consists of a sender converter (which converts Balanced->Cat 7) and a receiver converter (which converts Cat 7->Balanced).  To support double AES, each converter casing (die-cast aluminum / weather-proof) holds two XLR receptacles (twin Female XLRs for the sender; twin Male XLRs for the receiver)  and a RJ45 receptacle (weather-proof version).  A standard Cat7 cable with RJ45 connectors on both ends connects between the sender and receiver converters.

In deciding the wiring schema for the Cat7 converters, I have decide to go with the following layout:

Sender converter         Receiver converter
(1) Earth/Gnd Signal #1      (1) Earth/Gnd Signal #1
(2) Earth/Gnd Signal #2      (2) Earth/Gnd Signal #2
(3)   [unused]         (3) Earth/Gnd Signal #1
(4) Hot (+) Signal #1      (4) Hot (+) Signal #1
(5) Cold (-) Signal #1      (5) Cold (-) Signal #1
(6) [unused]         (6) Earth/Gnd Signal #2
(7) Hot (+) Signal #2      (7) Hot (+) Signal #2
( Cold (-) Signal #2      ( Cold (-) Signal #2

The advantage of this wiring scheme is that it will work for both straight-thru or crossover (Cat7) patch cable.

I have to admit that I was a bit skeptical at first, regarding how good the Cat7 cable will sound, when compared to using a short length (1m) audiophile grade digital coaxial cable.  I am happy to report that there were no noticeable degradation when running the 192kHz/24-bit digital thru the Cat7, when compared to using the high-end digital coaxial.  I am very impressed with the results.

Considering that I have 50ft of Cat7 running on each side, I now have a high-flexibility in positioning my speakers whilst maintain the best S/N ratio that digital audio signal can provide.

The sonic improvements gained by having DAC occurring at the proximity of the surround speaker is very significant.  And I would truly recommend this setup to any die-hard AV fans who are interested in getting extra-edge in sonic realism, which has been so elusive with conventional setup.

Happy listening! 

PS. Although I do use my SONY Qualia 010 as a reference headphone whilst calibrating the DEQX active crossover unit, it is unlikely that I am the same Audiophile ‘goatherder’ is referring to.  Glad to know that the full-digital setup fascinates you, goatherder. 

[pawelpe]

Coincidentally I have been working on the same idea - digital xover with speaker FR correction on PC. I have all the software written, tested - sounds REALLY good to me. I am doing a full digital path, i.e. I am taking SPDIF via a PC soundcard, cross over the signal digitally and then output it via SPDIF to a digital amp - Panasonic SA XR-55 (to be bought still, tests have been performed using a digital input of an old Yamaha HT receiver). But I did not manage to listen to the stereo, just one channel as the worst thing in all this endeavour is, as also this discussion testifies, multiple SPDIF output channel synchronization. To my knowledge there are three possible solutions for the PC (listed by the order of growing cost and possibly sound quality):
1. SoundBlaster Audigy - three SPDIF outs available but resampling . I have tested it.
2. Two independent soundcards synchronized by the means of linking the SPDIF out of one card to the SPDIF in of the other (the "master" card output must be forked). This is the path I am pursuing now but I am still not sure whether it will work and if yes how well it is gonna sound.
3. Lynx AES16 - multiple SPDIF output - high-end solution but still much cheaper than DEQX ?
What do you think about them, especially option 2 ?