A convolution based alternative to electrical loudspeaker correction networks - diyAudio
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Old 13th June 2015, 05:22 PM   #1
gmad is offline gmad  United States
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Default A convolution based alternative to electrical loudspeaker correction networks

The combination of full range drivers and convolution based correction can potentially make for a system which is simple and well behaved from both a frequency and time domain perspective. The provided guide however, will help anyone improve the sound of their system, regardless of their chosen loudspeaker type, using free software and a minimum of hardware. This guide assumes the use of a PC as the source, however, it is possible to hear the potential improvements afforded by this method by preprocessing music tracks with correction filters and burning to a CD.

After downloading and unzipping the attached file, you will find a 3 part text guide to get you on your way. This guide is not meant to be a substitute for the instruction manuals of the software programs that will be used, but I have tried to articulate the steps in a manner that might be understandable to someone for whom these processes are unfamiliar.

I recommend using my configuration files (the ones whose names specify the frequency dependent windowing length in cycles) to generate the filter, at least in the beginning. They will effectively provide a neutral response and attention can then be given to adjusting the target frequency response (if something other than a flat response is desired).

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Old 13th June 2015, 05:24 PM   #2
gmad is offline gmad  United States
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Default example result

Attached are some graphs showing the response of my left speaker (a small single driver hypercube speaker) from the listening position both before and after correction with the 4cycles filter (using the supplied highpass target file). The phase plot was done with a 6.5ms window to highlight the direct sound. There is no electrical network used for the speaker; the amplifier is connected directly to the speaker terminals.
Attached Images
File Type: png uncorrected frequency response.png (31.3 KB, 819 views)
File Type: png corrected frequency response.png (30.2 KB, 807 views)
File Type: png uncorrected phase response.png (32.7 KB, 799 views)
File Type: png corrected phase response.png (31.7 KB, 796 views)
File Type: png uncorrected impulse response.png (30.5 KB, 794 views)
File Type: png corrected impulse response.png (28.6 KB, 241 views)

Last edited by gmad; 13th June 2015 at 05:27 PM.
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Old 13th June 2015, 09:13 PM   #3
wesayso is online now wesayso  Netherlands
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Great! I hope this will start more people to look into this great tool set!
Scripting is included to check out the predicted response of the impulse correction.
So all you need to get started is to follow the steps outlined in the text guide.
You can actually see what it is going to do right after you've measured the impulses of both left and right speaker at the listening position.

If you can measure your speakers you can play with this, it's as simple as that!
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Old 13th June 2015, 10:21 PM   #4
gmad is offline gmad  United States
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I was encouraged to start this thread by xrk971 and wesayso. Wesayso, as a user of DRC Designer (a GUI version of DRC) has been kind enough to test the scripts for me. I would also like to thank him in advance for all the help I know he'll be providing in this thread.
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Old 14th June 2015, 03:30 AM   #5
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Hi guys. Thanks for this thread.

I've been using Farina's convolution and inverse transfer function (Kirkeby) plugins for Cool Edit and getting great results for near field alignment of smaller speakers. Prior to getting plugins I had mulled through DRC guide and all the terms and descriptions just seemed like psycho-babble. The posted plots of improvement didn't seem like much either.

I've had great success, but not after a number of experiences that make pre/post echo terms clear to me.

Frequency dependent windowing is what I am looking to explore more. I've manually done some band windowing and splicing that increase distance to which microphone may be placed from speaker without the correction becoming a modal mess. A more proper, and automated process with sliding window is a nice prospect.

I've read your primer, and indeed gone back through the DRC guide, looked at your various settings files and will be digging in.
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Old 14th June 2015, 10:27 AM   #6
wesayso is online now wesayso  Netherlands
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Good to have you looking into this! I'm still using DRC Designer, purely for ease of use.
Not with standard templates but with templates based primarily on gmad's settings. Of coarse I still play around with the variables, but nowadays mainly with the predicted response to see what does what. If I find something interesting it's easy enough to try and listen to it.
Pre-ringing is a reality with fir correction and it is key to keep an eye on that. But that all depends on how far you want to take things.
The basics (up to 4 cycle correction) gmad put in his templates are subtle enough to use for most users to get their feet wet. That probably won't lead to any big pre-ringing problems.

I think this thread would benefit from a step by step walk trough with some pictures added for guidance? As the thread from Perceval's setup showed, the initial results can differ a lot depending on room and speaker. So to have something up showing a visual aid to aim for would probably help make things more clear.
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Old 14th June 2015, 01:58 PM   #7
xrk971 is offline xrk971  United States
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Very nice work here - thanks for putting this together. It might be helpful for readers who are just getting into this to be able to see the basic outline of the process involved in text and embedded figures in Post #1 rather than downloading a 13MB zip file. The zip file would be utilized by those wanting to delve deeper and actually try the method with the config files as you have provided. I know it helps to get over the hump of reader's ease of access if it's readily apparent what the general process is without having to extract a zip file.

Also, if figures are embedded in line with text with captions that makes it easier too as figures in the common attachment area are confusing as to what they represent.

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Old 14th June 2015, 07:03 PM   #8
gmad is offline gmad  United States
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Hi, Barleywater:

I hope this proves to be useful to you. I will be interested to hear how things work out.


Thanks for the perspective. You have made good points. I guess I was unconsciously gearing this thread towards people who are already somewhat familiar with the idea of convolution based impulse response correction, but either weren't sure about where to start, or didn't want to invest in expensive software. As time goes on, I'll try to think of links to add to post #1 that give more of an overview of the process.
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Old 15th June 2015, 05:15 AM   #9
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Time to give back from all the help I got in using DRC.

Here's an intro guide, with pictures, showing how to get the sweeps ready for DRC use.

This is version 1. I believe it is complete, but I am not perfect, so please tell me if there's anything I should add or change.


Last edited by perceval; 15th June 2015 at 05:17 AM.
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Old 15th June 2015, 06:38 AM   #10
Pano is offline Pano  United States
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