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Old 11th March 2010, 04:35 AM   #61
Theo404 is offline Theo404  United Kingdom
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Quote:
Originally Posted by StigErik View Post
Hi-resolution Phase-Linear EQ will never be efficient
I beg to differ. I run detailed (read: high resolution) filters that are completely linear phase (wouldnt be able to get the flat phase response I have without them)... as I previously stated I run many filters with these qualities on a rather old system at less than 50% utilisation of resources. A modern system based on intels core architecture has probably 3-4 times the raw crunching ability of the dated platform my system is composed of and you say that this "plugin" consumes nearly 100% of resources?


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I can only answer for myself here: I use a soundcard (RME Fireface 800) that bypasses the kmixer. I also use a pure digital source (Squeezebox), so there is no A/D conversion involved either.
I dont understand. So you have a monumentally overpriced "prosumer" external sound card (with no doubt, the same well speced processing/dac chips that most soundcards use) and a squeezebox? Where does the squeezebox come in? Dont tell me you use digital outs from the RME device to send data to the squeezebox?! How is the squeezebox a "pure digital device" exactly? Its an embedded system that can decode audio formats and send them to an onboard dac... unless your just using it as a buffer in your audio chain, then its near pointless....


This has now gone a little too far off topic I guess.... I'd love to continue the discussion of certain peoples idiocy with regard to computer based hi-fi over in the computer section... god knows it could use some real debate, the SNR over there is ridiculous.
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Old 11th March 2010, 05:44 AM   #62
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I've some suggestions for the thread in the PC based forum. As it doesn't seem to have been started yet I'll post them here. Successful technology evangelists show people pathways for using the technology instead of complaining about other folks choosing to do things differently.

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Originally Posted by Theo404 View Post
Generation of these filters can be done in many ways, matlab/octave, numerous freeware programs, holm impulse....

Eq and phase correction filters, I feel, can be best created using holm impulse, the many ways to export measured data mean it can be manipulated in any way you like to create detailed accurate filters.
This workflow seems to be missing some steps. I assume you're referring to DSPreLab and not HOLMImpulse as that's where the crossover and equalization functionality resides but so far as I know DSPreLab lacks the ability to export FIR coefficients to something other than the DSPre. Like, say, a coefficients file for BruteFIR or SigmaStudio.

Among those numerous freeware programs are there any you'd suggest as easy to use for crossover and EQ design? It would be great to see a thread illustrating an accessible end to end workflow for how to get this stuff running. Preferably on a PC or Mac, or at least cygwin, and preferably one that has a reasonable chance of working out of the box---in particular, I'm curious how you'll address device driver availability for audio interfaces.

Recognize that folks who aren't electrical engineers have a substantial learning curve to deal with something like Octave or Matlab (not to mention my experience with Octave being it crashes so often as to be unusable and Matlab only being of use if you have the filter synthesis toolbox and a version that will run on your OS). Also recognize most folks are more interested in getting results than in tinkering with an OS. Unix variants, Linux included, tend to cater more to the tinkering mentality and, unless you have a system administration background, are not particularly accessible to the average user. This is coming someone who spent years doing network and system administration on everything from NextSTEP to OSF/1 to Solaris to Linux to Windows 3.0 up through XP. You and I can hack it, but unless you can articulate a value proposition for brutefir on Linux that's cost effective in terms of both time and money you're unlikely to see any significant adoption.

That said, you can find my posts earlier in this thread where I point out PLParEQ's relatively low return on value.

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Originally Posted by Theo404 View Post
I assume you have managed to fudge around the windows kmixer?
Some of the reaction you've gotten here is due to presenting as an OS fanboi. Taking the time to understand ASIO would help in that regard.
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Old 11th March 2010, 06:40 AM   #63
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Theo:
The squeezebox is my digital playback source. The digital output of the Squeezebox is fed into the Fireface, which sends the datastream through the filters that run in the computer, and then back to the Fireface on eight channels (4-way XO). The reason I choose the Fireface is that is has a unique combination of features found in very few (if any) devices on the market - like mic inputs, instrument line input, and great internal routing matrix and mixer. The only thing I'm missing is AES3 interface. I didnt buy the Fireface for its DAC's ---- they are not high-quality, but as a computer interface its great I think. To make it even worse, I have an external DAC in addition to the Fireface....

What I love with manually dialed-in classic EQ instead of generated FIR filters is that I can adjust to taste in real-time, sitting in my listening chair. Perfectly flat measured response is something I usually dont like too much either. To create a 4-way system with the PLparEQ plugin I need to run at least four instances of the plugin, that will generate four times the CPU load. Thats an other explanation for my high CPU load.....

Yes this *is* rather OT in this thread....
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Old 11th March 2010, 12:30 PM   #64
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Originally Posted by StigErik View Post
The reason I choose the Fireface is that is has a unique combination of features found in very few (if any) devices on the market - like mic inputs, instrument line input, and great internal routing matrix and mixer.
How long ago did you get the Fireface? This feature set is now normal in midrange interfaces (USD ~300). Granted, you'd have to spend more than that to match the box spec of RME's FPGA, but that's more than is required for running a four way crossover.
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Old 11th March 2010, 12:47 PM   #65
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Originally Posted by Theo404 View Post
I beg to differ. I run detailed (read: high resolution) filters that are completely linear phase (wouldnt be able to get the flat phase response I have without them)... as I previously stated I run many filters with these qualities on a rather old system at less than 50% utilisation of resources. A modern system based on intels core architecture has probably 3-4 times the raw crunching ability of the dated platform my system is composed of and you say that this "plugin" consumes nearly 100% of resources?
It's all about latency. FIR is clearly very expensive compared to IIR, but BruteFIR makes it manageable by trading off cpu utilization for latency. The Windows tools widely discussed here are for music creation not for general signal processing, and so generally need very short latencies. Crank your BruteFIR buffers down to 64 or even 32 samples and see what happens to your Athlon.

Having said that, for a music-only system there is no reason that a delay of 250ms or so is a problem, it's just that this isn't what most VST plugins are designed to do. I believe that convolver-vst manages this well, and it's free to boot.
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Old 11th March 2010, 01:22 PM   #66
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Originally Posted by twest820 View Post

This workflow seems to be missing some steps.
<edit>

Among those numerous freeware programs are there any you'd suggest as easy to use for crossover and EQ design? It would be great to see a thread illustrating an accessible end to end workflow for how to get this stuff running. Preferably on a PC or Mac, or at least cygwin, and preferably one that has a reasonable chance of working out of the box---in particular, I'm curious how you'll address device driver availability for audio interfaces.
I'm a long-time Linux/dsp xover tinkerer/experimenter, and even after 10+ years playing around with this stuff I think this is still unfortunately the crux of the problem. Theo isn't really incorrect in saying that some aspects of this problem are 'easy' in Octave/Matlab, but I think it's pretty telling that despite how 'easy' some of this is we still don't have anything like a usable freely-available filter generation package that the 'average joe' can use. I've started looking at tools again after a couple years on the sidelines, and for FIR filters it really appears that it's (((accourate))) or 'nothing' (i.e. hand-coded Octave scripts). I'm to the point that the ~$400 or so that accourate would cost me is starting to look like a pretty decent bargain despite the fact that I am "fully capable" of writing the Octave code to do what I want - it's patently clear that I will never take the time to do so, so the fact that I 'could' do it is a moot point.

I *did* find what looks to be a good Biquad designer in the form of the Hypex filter designer. This is aimed at exporting the results to their DSP amp products, but it is basically a graphical Biquad editor that allows importing of driver impulse responses and shows the individual filtered responses and the summed responses. It does not support Target responses, but it's better than anything else I've seen so far.
Of course, you still have the problem of translating these filters (which are Q based) into the flavor of biquad that your EQ uses - the Reaper eq for example uses 'Bandwidth' rather than Q, and it doesn't even look (at first glance) that B = 1/Q.

Fortunately, my perspective on EQ has changed as well. I used to be a Linear Phase guy, but my opinion now is that IIR is the appropriate topology for all crossovers and basic driver eq, and that only a single global FIR correction stage is really needed. I see the availability of things like the Dueland topology and the phase-coherent subtractive iir topologies more interesting at this point than a brute-force linear phase FIR crossover. Remember that Danley gets phase-coherent response out of his Synergy designs using purely passive xovers.

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Unix variants, Linux included, tend to cater more to the tinkering mentality and, unless you have a system administration background, are not particularly accessible to the average user.
Unfortunately, this is a perspective that I've grown to mostly agree with. I'm a 'Unix guy', having done fairly low-ish level Unix software dev since college and have always been a big Linux user. Even for me though, I've finally moved away from Linux for audio work simply because the overhead of managing the system and the dearth of good tools is just too much if all you care about is the results. The final straw was struggling to get my 'supported' firewire interface (Saffire Pro 24) working - it 'almost' works, but not quite. Conversely, in about 30 minutes of hands-on time or so I was up and running with Reaper, ReaRoute, Foobar and HolmImpluse with the ability to dial-in an IIR xover.

Now, the MPD + BruteFIR combo IS the best PC runtime playback platform that I've seen by a good margin - IMHO it's either that or a Squeezebox - anything else is cumbersome. I 'intend' to return to it once everything is settled, but the 'development workflow' is tedious when you're primarily experimenting with things.
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Old 11th March 2010, 04:40 PM   #67
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Quote:
Originally Posted by twest820 View Post
How long ago did you get the Fireface? This feature set is now normal in midrange interfaces (USD ~300). Granted, you'd have to spend more than that to match the box spec of RME's FPGA, but that's more than is required for running a four way crossover.
4-5 years ago I think... long time.

I have yet to find a cheaper interface that works with laptops, that has either ADAT or AES3 for multichannel digital I/O as well as multichannel analog I/O, SP/DIF I/O, mic input and the routing software of the RME. I think its *very* flexible.

Indeed - if 4-way XO with analog out was the only requirement, there are lots of other devices to choose from.
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Old 11th March 2010, 07:22 PM   #68
cuibono is offline cuibono  United States
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Quote:
Originally Posted by dwk123 View Post
...Fortunately, my perspective on EQ has changed as well. I used to be a Linear Phase guy, but my opinion now is that IIR is the appropriate topology for all crossovers and basic driver eq, and that only a single global FIR correction stage is really needed...
This is an interesting conversation. Could you explain a little more of this in lay terms? I've just started playing with linear phase software, so I'd like to know more, but I just don't know much about all of these different ways of doing things. Are you saying you'd use a single FIR filter to get things phase linear, and let IIR handle the rest of the XO/EQ? I'm just guessing here...
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Old 11th March 2010, 07:26 PM   #69
cuibono is offline cuibono  United States
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Quote:
Originally Posted by Theo404 View Post
I'd love to continue the discussion of certain peoples idiocy with regard to computer based hi-fi
Assuming you have something useful to share, nobody is going to listen to you with an attitude like this. Its immature, and it is exactly this sort of approach that lower the SNR.

Last edited by cuibono; 11th March 2010 at 07:30 PM.
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Old 11th March 2010, 10:11 PM   #70
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Originally Posted by dwk123 View Post
I've started looking at tools again after a couple years on the sidelines, and for FIR filters it really appears that it's (((accourate))) or 'nothing' (i.e. hand-coded Octave scripts). I'm to the point that the ~$400 or so that accourate would cost me is starting to look like a pretty decent bargain despite the fact that I am "fully capable" of writing the Octave code to do what I want
I hit the same point with Linux for my personal stuff back in 1998, though I continued to use various unixen for work up through 2004. Good data, thanks, especially as I'm using a Saffire as well. If I didn't have a requirement for linear phase I'd just use a Motu Ultralite but, as it stands today, the ~$125 incremental cost riser for a linear phase PC crossover's quite attractive compared to fixing bugs in third party Linux device drivers.

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Originally Posted by dwk123 View Post
I see the availability of things like the Dueland topology and the phase-coherent subtractive iir topologies more interesting at this point than a brute-force linear phase FIR crossover. Remember that Danley gets phase-coherent response out of his Synergy designs using purely passive xovers.
From my investigation Duelund's a major hassle to implement with dipoles due to the limited agility in crossover points and slopes. Implementing a four way linear phase crossover on the PC is much easier.

Is Danley using Dunlavy's approach or something else?

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Originally Posted by dwk123 View Post
MPD + BruteFIR combo IS the best PC runtime playback platform that I've seen by a good margin - IMHO it's either that or a Squeezebox - anything else is cumbersome.
Cumbersome how? I've found Bidule+Allocator+PLParEQX3 quite easy to work with.

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Originally Posted by cuibono View Post
Are you saying you'd use a single FIR filter to get things phase linear, and let IIR handle the rest of the XO/EQ?
That's certainly one option. It'd be interesting to see how CPU load and latency compared to efficient time reversed IIR implementations like Allocator or FFT based approaches like PLParEQX. I'd expect IIR+FIR to win on latency and lose on CPU and usability (not that the IIR part is particularly difficult---Allocator Lite's all of USD 60).

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Originally Posted by StigErik View Post
I have yet to find a cheaper interface that works with laptops, that has either ADAT or AES3 for multichannel digital I/O as well as multichannel analog I/O, S/PDIF I/O, mic input and the routing software of the RME.
You just described the Saffire Pro 40 I eBayed for USD 350 (new, shipping included) a couple months ago. In comparison the Fireface 800 is around USD 1500 on this side of the pond (the 400 is about USD 1000).
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