Bennett Prescott wrote on Sat, 08 January 2011 11:11 |
Friends, Romans, Countrymen...
I am going to write an article about different DSP platforms, in an attempt to have a semi-definitive source to point people to the next time I get asked why those Driverack settings sound so funny in the KT processor.
I would be touched if y'all would do me an enormous favor and help me get measurements from different processing platforms. I have designed an imaginary loudspeaker preset that I think will stress the differences in their filter definitions. If anyone thinks they have better ideas, speak now or forever hold your peace. I am trying to make it somewhat realistic while fitting within the filter capabilities every processor is likely to have. Any reasonably mainstream processor welcome. These exact frequencies and bandwidths may not be available (on purpose), please get as close as possible.
If you would like to help, please program these filters into whatever DSP you have at hand: High Pass - Bessel - 97Hz 18db/octave Bell - 280Hz - 2 octaves/0.66 Q -4.5dB Bell - 176Hz - 0.6 octaves/2.39 Q +5dB Bell - 6.35kHz - 1/8 octave/11.54Q -8dB Shelf - 8kHz - 1.6 octave/0.86Q/6dB +5.5dB
Measure with Smaart, using the standard internal pink noise source as a reference. Use 16 averages, 48k sample rate, and 24bit, no smoothing. Use auto small to set your delay compensation. Please take a measurement with a 16K FFT and one with FPPO. If you could also send me an IR file that would be invaluable.
Please label your measurements and email them to me, don't post them here... I need to know which processor which measurement came from, but I don't want everyone to know. Anyone who wants to go even further and put in bandwidth instead of Q and take another measurement of that would receive another free Internet.
bennettprescott at gmail dot com
Thanks in advance to those of you with a little time to waste and some measurement chops!
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Good luck... I hope you get a good response, maybe there are enough people with measurement software out there now. Some of us have been pissing up this rope for a while. The subject has been broached before, but usually with arms thrown up in air, and cries of all is lost, we are damned, time to consider Hari Kari. I hope you are planning to be more constructive than those earlier expositions.
You seem to be hitting most of the known offenders, Q and filter treatment at passband extremes. [insert my well worn rant here about lack of official standards definitions for Q in boost/cut sections, yadda yadda].
Are you attempting to come up with a nomograph and/or equations to help users translate between different DSP Platforms? Or just group them by similar behavior? I think Rane has done the most work in that area to date, but last I looked they only covered a limited number of DSP platforms.
http://www.rane.com/note167.htmlIf trying to come up with reliable translation metrics you might need more/different data points, but I am not smart enough to tell you exactly what to ask for. I find it remarkable we haven't resolved this yet, but I have only been an uninvolved observer without a strong personal or business motivation to deal with this.
In my judgement we don't really need a firm standard that would create winners and losers (like pin 2 hot), just clear explanations from the sundry DSP sellers, of what "they" mean when they say... XYZ bandwidth or Q... back when I was writing for RE/P I actually polled all manufacturers asking which XLR pin they used as hot....and published the results in my column (in the 80s before AES standard). Since you are writing your article for a magazine, ask your editor to make a similar request of all manufacturers (using his advertising list), like mine did for me back in the day. If the manufacturers refuse to honor this request list them in your article as unresponsive to embarrass them into responding for a follow up (this may require an editor with cohones, some are afraid to tread on advertisers).
I think I even started some work on a questionnaire for this within the last few years, also asking for a contact engineer from inside each company for follow up, but the editor I was working with flaked out on me, so this never happened. Then I got busy with real work.
I wish you better luck than I had, with this Babel.
JR