Computerized Crossovers

[johninCR]

I keep copies of all my music on my computer and use it as my primary source just for convenience. I really enjoy building speakers but I dislike crossovers and the host of problems they create. I was thinking since the music is already in the digital domain, why can't my computer do the work of a crossover? I'm not talking about filtering or having slopes. I'm talking about a clear clean separation with no phase shift. eg If the frequency is less than 80hz send it to the soundcard port for the sub, if it's greater than or equal to 80 and less than 500hz, send it to the woofer, etc.

Is there any software available that does this and controls the multiple soundcards necessary to accomplish the biamping or triamping that would be necessary?

[tiroth]

Originally posted by johninCR
I'm not talking about filtering or having slopes.

Yes, you are. With FIR filters it IS possible to have "brick wall" type filters of 100dB/octave, but these are not without their own issues.

[HDTVman]

John, you need to understand that the computer doesn't know what the bits and bites are. It just sends it off to the D/A converter and away it goes.

Tiroth is right. If you want the computer to do the work of a crossover then a minimum of 3 FIR filters need to be running.

FIR-1 80 Hz and below, both channels?
FIR-2&3 above 80 Hz, one for each channel.

Custom hardware would be faster but not cheep.

Good luck

[johninCR]

Originally posted by HDTVman
John, you need to understand that the computer doesn't know what the bits and bites are. It just sends it off to the D/A converter and away it goes.

Then it makes sense that it wouldn't be so easy.

Are there some relatively cheap software packages that would give you the fuctionality of something like the dbx Driverack 260 speaker management system in your PC?

[sub-optimal]

I use a home-brew software-based crossover for my orion-ish active dipoles. It runs a real time synthesis/dsp software environment called supercollider. I use piles of second order sections (IIRs) to emulate the various analog filters Linkwitz uses, rather than using FIRs. So my crossovers have the same freq and phase response of their analog prototypes. I use lspcad to model the system, then implement the filters in software.

You can definitely build your own computer based driverack or dcx2496 type device. It just costs 10x as much and is 100x more effort

[azira]

I used to run 2 soundblaster 16s in my system before direct sound came about. The problem was that each sound card only had one wave table so if you were playing MP3s then you couldn't hear any dings or beeps or etc (video game sounds) from your system. The solution, run 2 soundcards and have WinAmp directed towards the 2nd card.
I also used to write some DirectX software for playing back videos and displaying pictures and that kind of stuff. It is really easy using the sample code to come up with a basic MP3 player.
I think that if you're a software kind of guy and willing to put in some time, it wouldn't be very difficult to drive a couple of soundcards from a single stream if you had the right FIR/IIR equations.
It'll be some effort, but assuming you had the soundcards, the cost wouldn't be that much.
--
Danny

[freelancer]

I was discussing exactly this topic with a couple of friends a few days ago.
Bear in mind that I'm a newbie to audio so I might be talking nonsense.

The first impression one gets after wading through diyaudio is that crossover
design is tough stuff, almost magic. As a software guy my instinctive
response was "well, let's do it in software then". The idea is to leverage 5.1
hardware to drive a bi/tri-ampable stereo pair.

PC with multichannel soundcard (creative audigy etc., although you can get
cheap 5.1 cards for lunch money)

PC has audio in digital form, either on disk or in a CD.

DSP software on the PC splits the audio into n streams (as many drivers as
you have) and dumps each one to one channel of the soundcard. Clearly
n <=6 which limits how many drivers you have in your system.
This is the crossover.

DACs on the card convert these digital samples to analog signals.
Now connect the line outputs of the card to the analog inputs of a 5.1
receiver/multichannel amp/separate amps. Connect the output of the
receiver to each driver of your bi/tri-ampable speakers.

Points to be noted:

1. Since the crossover is in software you can fiddle with the settings to your
heart's content.

2. Several 2-channel cards can be used as someone has pointed out.
However, it is difficult to synchronize streams across two cards. Better
to have a single multichannel card to which you supply "packets" of
6 samples each, which will be decoded and outputted together
on all 6 channels.

3. The XO DSP need not be done in real-time. You can process each
2-channel (stereo) "wav" file obtained by ripping a regular audio CD
track offline to get a 4/6-channel pcm wav file. This file can be easily
played with minimal CPU requirements.

4. You can create several such XO-ed wav files and instantly switch
between them, allowing easy XO comparisons.

5. The biggest problem with this approach is that computer parts typically
have much lower fidelity than demanded by audiophiles. One way out is to
convert files obtained above into DD/DTS audio tracks and use a high-end
player which recognizes these formats. Once again, we can abuse the
multi-channel outputs to drive several drivers in a stereo setup rather
than the surround channels.

[johninCR]

Freelancer,

That's exactly along the lines of what I was thinking, but who is correct, you or HDTVman? Can it all be done in the digital domain? If it can be then I'd foresee the future being modular sound cards, giving you the ability to add as many ports as you like. Each would have the amplifier(s) built right in. If brick wall type xovers are problematic, fine, make the xover slopes variable.

In the meantime, are there any good cheap (free) DSP software packages available? I'm not a software guy at all, just a user.

[lucpes]

http://www2.gol.com/users/pcazeles/asioxo.htm

PC music players

[johninCR]

Originally posted by lucpes
http://www2.gol.com/users/pcazeles/asioxo.htm

PC music players

Thanks Lucpes, that's exactly what I was talking about.