A how to for a PC XO.

[Audiophilenoob]

Originally posted by Archmage

- Heh, I found a source for just ONE of those PHL 1120's, so I'm sticking with my Excels for Revision1 - maybe I'll like them

keep it on the D/l

this knowledge is for the privileged otherwise our designs won't be unique

[Audiophilenoob]

Originally posted by Archmage
I think I'm going to settle for an E-MU 1820m

the M version I can't find for cheaper than $375 from an online store

sry

[elambert]

Well dadgumit, Shin, I think you may have started a new trend.... Now I have to go and get a capable card and software.



More money down the black hole that is audio

[weinstro]

ShinOBIWAN,

I find this solution to be very interesting. However, I have a couple of questions I hope you don't mind responding to:

1. I would probably be more interested in performing the XO function just to drive a pair of subwoofers, sort of a 5.2 type system. How could this be configured to provide some level of bass management support? My front drivers aren't bad, but they're definitely not full range capable. For example, DVD-audio with a dedicated subwoofer channel vs. standard redbook CD playback.

2. How do you recommend controlling volume and switching? I have tuner, LP, DVD-audio, and SACD players.

3. Way back in post #5, you said:

Remember that you'll need to have light tasks for it such as 2 channel audio for it to work flawlessly if you use an all in one solution. I can't stress that enough because if you start playing DVD and especially high definition video and games you will start to hear all manner of stranger noises from the speakers that could actually potentially damage the HF drivers. Those strange noises are things like pop's, stuttering, cracking, hiss etc.

Can you expand on this, please? What's causing the noise, and does it appear only on 2-channel sources?

Very interesting what you have built here!

Thanks and regards,

Rob Weinstock

[ShinOBIWAN]

Originally posted by weinstro
[B]ShinOBIWAN,

I find this solution to be very interesting. However, I have a couple of questions I hope you don't mind responding to:

I'll try.

1. I would probably be more interested in performing the XO function just to drive a pair of subwoofers, sort of a 5.2 type system. How could this be configured to provide some level of bass management support? My front drivers aren't bad, but they're definitely not full range capable. For example, DVD-audio with a dedicated subwoofer channel vs. standard redbook CD playback.

Well I've got a single LFE channel, 3 full range channels and 6 channels to create a 3-way stereo XO. That's a total of 10 channels.

If you want 5 full range with 2 filtered channels for LFE then that's even easier than the above.

What I'd do is put a high pass at 80hz in all the 5 full range channels. Then for the LFE channels simply drop in a low pass at 80hz. You can then add EQ and delays if required.

2. How do you recommend controlling volume and switching? I have tuner, LP, DVD-audio, and SACD players.

Switching will be different from card to card. The way it works with the RME is a bank of 8 presets. The can be convieniently accessed with ALT+1,2,3... etc. In these presets you can assign levels, routing and ultimately source assignment. Takes a while to setup but once its done its incredibly easy to switch.

I have the shortcuts labelled up on my palmPC to actually indicate each presets function there is then a wireless link to an Xlobby client on the dedicated XO PC which automates signals from the PalmPC to TotalMix which controls the RME. This means source selection works just like a traditional remote control. I don't even need a monitor for the dedicated XO PC.
One thing I haven't managed yet is to find the control codes for the volume control in RME's TotalMix, so I can't control volume directly but can setup presets with various volumes and select them from the palmPC. For instance I've got a reference level setting for HT and a night time level for HT and music.

I can control virtually every aspect of transport controls in all my players from the PalmPC too.

The most simple way to control all this is of course with your mouse & keyboard from the desktop in XP. Its nowhere near as elegant as the PalmPC solution though.

Can you expand on this, please? What's causing the noise, and does it appear only on 2-channel sources?

The noises are caused by dropouts and processing halts in the plugins that form the basis for the XO. When the computer get overwhelmed you'll notice that audio stops or more likely will repeat and stutter as it gets 'stuck' in a processing bottleneck.

This is very dangerous for you tweeters and the level can be quite loud sometimes the line-level signal is driven into distortion and whilst your amps won't be clipping they will be playing a clipped signal.

A good example is try to setup a stereo 3-way XO with DRC and phase. Playback a lossless audio file at 44kHz then try unzipping a 1Gb file. The fact that processing is required for decompression and hard drive accesses means that you'll start to hear audio nasties.

Simple stuff like web surfing whilst running the XO is fine but you can imagine the strain when filtering and EQing 5.1 channels of audio! That's why you need a dedicated PC with serious horse power.

[ewildgoose]

I haven't read the entire thread here, it has just been pointed out to me from a link on avsforums.

You folks may be interested in documenting some of your findings on a site I have setup to try and help document this room correction and digital XO stuff

http://www.duffroomcorrection.com

The main technique I am using is a PC based surround crossover with subsequent room correction. I have written a little tool which will take a very high quality room response measurement. I then use some software called DRC to "invert" this and correct the audio as much as possible (this is non trivial by the way).

I then use a bit of linux software to implement the crossovers and downmix any 5.1 surround to a kind of 4.2 signal. All this with HUGE filters on each channel to do the correction is done in less than 10% CPU on a P2.8Ghz. There is another 12%+ for the resampling though, but this leaves plenty for the machine to perform other HTPC duties

Obviously if you don't like linux or want to use one of the fancy cards discussed here then you can use something other than Brutefir, but the previous stuff should all be very relevant

Oh, and the 4.2 means four speakers around the corners of the room and then I have a stereo infinite baffle sub - this means 4x 15" long throw woofers burried in the floor in an "infinite" sized box (technically the entire underfloor space). This gives a bass response with very low distortion which extends flat below 10Hz...

Please feel to contact me via the site for more info on my setup, but please also create an account on the site and document your own systems, and writeups on any of the technical details for doing this stuff would be appreciated. It's quite hard to find info on digital XO stuff, and so I created the site to try and bring it all into one place

Good luck all

Ed W

[ewildgoose]

Hmm, I have just read the first post in this thread. Update to the above:

- My technique above can be performed using only free software.

- Using Brutefir on linux I can run a huge number of filters with very low CPU usage. Brutefir uses FFTW in the background (Fastest Fourier Transform in the West in case you were wondering...) - there are instructions on my site on creating a bootable system running Brutefir in a 4.6Mb compact flash memory stick (OK, so compare that with a stripped down windows install and tell me you can do better?)

- I also use an RME 9632 and the quality is excellent (can't hear any difference between it and my old Meridian 508.24 CD player, which is supposed to be pretty good). I also own an RME 96/8 PAD and I can't really hear much difference between it and the 9632...

I don't really think the quality of the soundcard is your biggest problem. Even a crappy built-in soundcard can reach significant quality levels if you go down the DRC route

- "DRC" is an extremely powerful bit of software and is capable of much higher levels of performance than the software described in the original thread. It will try it's hardest to flatten the freq response, but more interestingly it will try and correct phase response to some extent (this will make the correction more position specific, but it's quite bearable). The end result is that the stereo image jumps out in size quite dramatically (you can hear the room that the artists are in, rather than the sound of your own room)

This is not to knock the original poster in any way. There are many, many ways to skin a cat and your solution looks FAR more user friendly than the method I am using. I would be interested in having you transfer your notes to the web site if you are willing because it's a very interesting writeup?

Good luck all

[JoshK]

Gooseman, your solution is one that I am interested in exploring, for the reason that 1) it is in linux which I would prefer to use and really good DRC (free) software is written in linux and 2) its free. I also am looking to replicate ambiophonic sound in my room as this is the greatest improvement in audio that I have ever heard myself. A linux processing box seems a natural solution.

[Llafriel]

I'm trying out Console with my M-Audio Revolution and it seems to be working. But it only works with the analog inputs. I'm unable to route sounds from windows through Console. Is this what "Internal routing of digital signals" is for? Or am I missing a setting somewhere? I use my pc as an htpc and do not use any external soundsources.

[ewildgoose]

Originally posted by JoshK
Gooseman, your solution is one that I am interested in exploring, for the reason that 1) it is in linux which I would prefer to use and really good DRC (free) software is written in linux and 2) its free. I also am looking to replicate ambiophonic sound in my room as this is the greatest improvement in audio that I have ever heard myself. A linux processing box seems a natural solution.

Well, linux has it's pros and conns, but the majority of the solution is multiplatform (eg my IR recording app and DRC are both multiplatform). Brutefir is just a way to implement the filters and there are other ways - I don't think the quality of implementation is too important in general anyway

Ambiophonics is another difficult topic - there is nothing on my site about it yet, but I might try and knock up a quick summary for you later (or please have a go yourself, just link in the main sites to read up on at least). The best place to start is probably the AlmusVCU site (same author as brutefir) - he has some really nice software that you might want to play with, but be aware this is a big and badly documented subject and you are going to have to do a lot of research and write questions to the big wiggs in the research game (also read the sur-sound list I guess?)

Good luck. Please do document your findings on my site

Ed W