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Old 24th February 2011, 11:49 PM   #1
Tenson is offline Tenson  United Kingdom
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Default PC Crossover Software

I'm keen to make a PC crossover that is state of the art. I have the hardware side sorted, I'll use a Lynx AES16 card and connect a quality ADC and 4 stereo DACs. I'm going to need 8 channels.

I'm not sure where to start on software. I read some of Shinobiwan's thread but it was made in 2005 and seems a bit out of date. He was using Console, Waves and stuff. I think since then I have heard him mention Accurate (it's something like that) and I have also heard of BruteFIR.

I don't really know much more than those names though. Where do I start? Do I have to use one software to generate the filters (which are what format?) and then another program to convolve?

Is there a good guide somewhere? I had a look at the BruteFIR website but it's not very friendly IMO.

Ideally I'd like to run Linux and use a solid state hard disk and a fixed state of install so I don't need to shut down, I can just power it off and it will load back again kinda like a live disc or returning from hibernation.

Guidance appreciated!
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Old 25th February 2011, 12:18 PM   #2
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Hi Simon,

Its been some two years or so since I fiddled around with any of that stuff so its all starting to get a bit fuzzy with the old memory. I'll try to give some advice on where I was at during the peak of it though. A quick disclaimer though - I've long since abandoned the PC route because I just got lazy and wanted a setup that needed zero attention. PC's do need a little work every now and then when you want audio and video playback. Less so if its just audio, actually once I was happy with the result I doubt I'd have had to touch anything if it were just that.

I now use the DEQX as a set and forget device and works quite nicely for my needs. There's some drawbacks like only 3-way and the software isn't anything like as capable as what you'd normally find on through the PCXO route so I concede its not as powerful a tool nor are the filters as sophisticated. What it does do extremely well once setup is just remaining transparent to the end user. You turn it on and it works.

My most preferred PCXO option was Acourate generated filters run through a regular plugin such as convolver hosted within Console. There's other methods but this one really worked for me at that time and the quality was hardcore.

Shameless plug here but what the hell. I no longer have any use for Acourate and I have a registered copy which isn't particularly cheap but if you fancy giving it a go I'd be happy to sell it for 100. Acourate is normally around 270-290 depending on the exchange rate for Euro>GBP.

I wrote a little(unfinished) manual at the time which might give you an idea of what to expect:

Acourate Manual.pdf

This in combination with Uli's tutorials and the Acourate user group will pretty much make you completely familiar with all the steps needed to create good filters.

Other software is:

Convolver for the filters: Convolver — a convolution plug-in
Console for the host: console sound modular studio : Host for VST Plugins & DirectX(DX) | How to use | Buying | Useful Information
Voxengo Latency Delay for time alignment of the drivers: Audio latency compensation plugin (AU, VST) - Latency Delay - Voxengo

One thing I would recommend, once your set up and decide its the route you want to take, is a good measurement mic. The Behringer ECM3000 isn't particularly accurate above about 1k or at least the two I had weren't and the generic correction files are a band aid. Batches have been confirmed to vary in the top octaves. I now use the 'budget' Earthworks M23 but if buying new then they're not particularly cheap at around 300, I got a mint used example off a seller in the US for just 130 including the postage.
There was a real tangible increase in the quality of the filters once I redid them with the M23. The mids and highs were more solid and focussed and imaging was further improved if I was subjectively trying to describe the difference.
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Old 25th February 2011, 12:52 PM   #3
Tenson is offline Tenson  United Kingdom
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Thanks very much Ant!

I'll take Acourate Please PM me your paypal account.

What format are the filters? I sort of assumed they are generated impulse responses by which the audio is convolved?

Is it always necessary to use a separate plug-in to handle delay, can't this be part of the filter or done in the convolver?

On the subject of delay, processors are more powerful than in 2005, do you think delay could be low enough to handle video these days, or is it more limited by the minimum buffer of the sound card? I'd have thought <5ms should be okay?

I take it you never had a go with BruteFIR? Seems like my best route is to get familiar with Acourate and test it with an easy Windows convolver that has a nice GUI. Once I know that is running well I can focus on making BruteFIR do what I want in a dedicated Linux setup.

Anyone here know how well Lynx cards are supported in Linux?

P.S. I use a Beyer Dynamic MM1 mic. Someone on here once wrote a review of lots of measurement mics for a US pro audio mag comparing them to a top B&K. The Beyer MM1 apparently had the most accurate response, although a bit more noisy than some due to its small capsule. You will be pleased to hear the Earthworks was the second most accurate and had lower noise.

These days I also have easy access to an anechoic chamber, an air-field for bass measurements and some B&K equipment should it be needed

Last edited by Tenson; 25th February 2011 at 01:06 PM.
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Old 25th February 2011, 01:01 PM   #4
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Accurate is great. I have got some stuff here. Part of Shin's tutorial is here too

The Building of a Pure Digital System
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Old 25th February 2011, 01:01 PM   #5
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Have a look at Frequency Allocator Transient Perfect loudspeaker DSP tools . Windows DSP speaker crossovers. for another option that includes a VST shell, so there is no need for any other software. It allows you to dial in a large variety of filters, up to 7th order, plus various shelving and parametric equalization options. No, it won't do a real brick wall filter so you'll need something else if that is your goal. I haven't compared it to other options, but with a modestly powered Celeron based machine with an M-Audio FW410 it sounds very nice.

You can download a demo to give you a feel for it. The Light version doesn't include the phase arbitrator portion, which allows a very low latency crossover at the expense of transient perfect crossovers.

There is also a winamp output plugin so you can stay in the digital domain without any routing software.
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Old 25th February 2011, 01:36 PM   #6
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Quote:
Originally Posted by Tenson View Post
Thanks very much Ant!

I'll take Acourate Please PM me your paypal account.
I'll send you a PM with paypal details but I'd like to contact Uli and make sure its OK to transfer the software license to you before doing so. Acourate has a built in copy protection that analyses your pc hardware and generates a code for Uli's use to send you an unlocked and tailored .exe for that specific PC. Right now its locked to my pc so I'll have to get that sorted for you.

Quote:
What format are the filters? I sort of assumed they are generated impulse responses by which the audio is convolved?
They're double precision floating point format or .dbl. Convolver and most other plugins will accept these. Acourate will also create single precision floating point or .pcm

Quote:
Is it always necessary to use a separate plug-in to handle delay, can't this be part of the filter or done in the convolver?
I did it that way because it was easy to mess around with on the fly. I wouldn't recommend adding the delay in the filters because you'll loose resolution filling it with zero's for the needed delay. You can do so in convolver but its set through a text configuration file and I always found it a pain to keep going in and changing the values when needed. Perhaps better would be to use the delay plugin to nail your delays then use the text config for convolver when setup is finalised.

Quote:
On the subject of delay, processors are more powerful than in 2005, do you think delay could be low enough to handle video these days, or is it more limited by the minimum buffer of the sound card? I'd have thought <5ms should be okay?
Its just the nature of FIR filters, they'll always have an inherent delay although if you reduce the resolution, or in other words the number of correction points, this can be made mute. The DEQX uses this approach to get around 10ms of delay which is fine for video. The lower the frequency the more the delay so they took to making 1000 tap filters for the high frequencies, and 4000 for the rest. That's basically like a 4000 band EQ and plenty of control. The taps are spaced out in a linear fashion so that's where the resolution part comes in, the more taps the smaller the gap between them and the more exacting control you have on the correction points instead of it being a hz or two out. I used 65536 taps on each individual filter which is a huge amount really and introduces a second or so delay at 96Khz sample rates I used - everything was up sampled or down sampled to this but you can create 44khz filters should you wish.

If you really don't want any delay at all then Acourate will create IIR too. I believe BruteFIR allows to switch between different sets of filters on the fly with relative ease so you could have a set for movies and another music.

As to the processor speed required for the general computation power needed to run things smoothly your easily covered with todays cpu's. Just get some thing quad core and around 3ghz+. Plenty of power for any eventuality.

Quote:
I take it you never had a go with BruteFIR? Seems like my best route is to get familiar with Acourate and test it with an easy Windows convolver that has a nice GUI. Once I know that is running well I can focus on making BruteFIR do what I want in a dedicated Linux setup.
Never played around with BruteFIR but I'd say its probably better than convolver. Its certainly the best option for a linux box.

Quote:
P.S. I use a Beyer Dynamic MM1 mic. Someone on here once wrote a review of lots of measurement mics for a US pro audio mag comparing them to a top B&K. The Beyer MM1 apparently had the most accurate response, although a bit more noisy than some due to its small capsule. You will be pleased to hear the Earthworks was the second most accurate and had lower noise.

These days I also have easy access to an anechoic chamber, an air-field for bass measurements and some B&K equipment should it be needed
Good to hear. The quality of the mic makes a larger difference than I considered.
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Old 25th February 2011, 02:52 PM   #7
Tytte71 is offline Tytte71  Norway
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Another option would be Audiolense XO (http://www.juicehifi.com). I use this for my HTPC (LYNX AES 16) to generate filters for JRiver Mediacenter. JRiver can use DRC with up to 32 channels directly without any additional channel routing software.
Instead of ADC I connect the LYNX AES3 ports directly to my Lyngdorf amps - similar to the Tact amps. The Master Lyngdorf amp controls the sound level on all the amps, meaning always full output/dynamic range from JRiver.
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Old 25th February 2011, 03:46 PM   #8
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Might want to look at the Bodzio software tool
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Old 25th February 2011, 03:56 PM   #9
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Quote:
Originally Posted by Tenson View Post
I'm keen to make a PC crossover that is state of the art. I have the hardware side sorted, I'll use a Lynx AES16 card and connect a quality ADC and 4 stereo DACs. I'm going to need 8 channels.
You could start by choosing a card that has a Linux driver - that would help.

RME make something similar, and I *think* that has driver support.

I had been looking to do something similar but came to the conclusion that its somewhat cheaper to use either the GroundSound crossover-in-a-box (per side), or just build or buy a pair of fanless atom-based PCs and sound cards and use a complete PC-and-soundcard for each side. There's more choice in that case, although I guess you'd want to be careful with throughput and brutefir - I was just going to use biquads - so you might want a different CPU base.

If you accept resampling, or that you will split a single spdif into both sides (and choose by config) so that both are using your SPDIF source as clock master, then it might be easier.
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Old 25th February 2011, 04:01 PM   #10
Tenson is offline Tenson  United Kingdom
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Damn isn't it possible to use the Lynx in Linux? I got it cheap from someone on a forum so jumped at the opportunity.
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