01-18-2013 05:42 AM - edited 01-18-2013 08:15 AM
Wondering if there are any potential issues with these settings. I have A/B between passive and;bi amp and the overall performance of the 715 is improved. The setup:;Crown ITech 4000, channel 1 low's channel 2 highs. It was recommended that I use the tunnings found in the dbx 4800. Supposedly the the ITech DSP is based off the 4800. Please advise.
HPF 91.86 Hz LR 48
LPF 1.14kHz LR 48, ;gain -1.7db
Delay .208ms/ 0.23ft
HPF 1.12 kHz LR 48
gain - 16db (I adjusted this to -13 db to brighten up the high end)
1. 6 db octave Shelf 183.72 Hz + 3db
2. Bell 500Hz -1.5 db Q .92
3. Bell 93.6 Hz +3.5db Q 2.92
4. Bell 250Hz -2db Q2.92
1. Bell 12.7kHz +6.5db Q 2.46
2. Bell 2.38khz -3db Q1.95
3. Bell 5.55khz -3db Q 4.13
4. Bell 1.62kHz -1.8db Q 1.74
RMS 800w 4 ohms attack 4sec release 6 sec
Peak 110v 4 ohms attack .010sec release 1sec
RMS 75w 4ohms attack 4sec release 6sec
Peak 30v 4ohms attack .010sec release 1sec
Thanks for fixing the forums!
01-18-2013 08:30 AM
Is this for using with a sub or not?
What I see that does not match my experiences developing DSP for client SRX series is that the 91Hz HPF is questionable or plain wrong unless using with sub. There is a LF shelving eq that doesn't make sense either.
In the HF section, -16dB of HF gain relative to -1.3dB of low gain is too much difference, The net should be between 10 & 12dB which your change to -13dB corrects for.
You might take a look at the 260 settings and see what the differences might be. I have found there to be errors in the 712 settings throughout the DSP models so I would expect this to be possible on the other models.
Also, I would take the RMS limiters down to an attack time of 1 scond on the HF as well. If you have a 4 second "loss of good judgement" event in the HF range, you have big problems happening and that's an expensive to replace.
01-18-2013 09:04 AM - edited 01-18-2013 09:21 AM
01-18-2013 08:08 PM
It's possible that the HF lift eq extends low enough to require less HF gain. I can't find any of my info or worksheets on the 715 to doublecheck.
Every engineer has their own personality when it comes to developing DSP. Many come to the same or similar point but some are just plain goofy with multiple wrongs attempting to make rights...
01-19-2013 05:38 AM
01-19-2013 07:56 PM
The tunings you came up with for the 712 a while back are much better than the DR 260 settings.
Would you recommend setting the RMS limiter attack time to 1 sec for the low and sub? All my RMS limiters are set at half the drivers RMS rating.
My tunings address specific issues and are not written in a vaccum. Sometimes (often), simpler is better, so when looking at what is going on I tend to address and correct using the least intrusive solution.
It seems that many folks will take a convoluted route and may contain additional unidentified artifacts that make some parts of the solution worse than the problem. My engineering adviser in university was an ag engineer, a very wise old man that studied very much the big picture and drove home that the solution should not make the problems worse... do no harm. This is the basis of everything I design.
As far as the lows and subs, with that RMS threshold, I do not see any problem with 4 seconds attack. The reason has to do with the thermal inerta of the VC as well as the fact that T(i) (initial temp) is going to be reasonably conservative because of the threshold. Since it's a dynamic problem, there is no one exact answer but a conservative approach is a good idea.
02-01-2013 04:47 PM
02-01-2013 05:51 PM
I used these settings for a recent gig and had to adjust the levels dramatically in every bandpass. With the original settings I was clipping my inputs way before any output limiting. I adjusted the subs to + 12db, mids +10db and highs to -3db. This did the trick and the system sounded/performed great. I was told a while back not to run any bandpass below 0 with the ITechs.
That would indicate a poor DSP algorithem IMO. Where did you have the input sensitivity controls? On some DSP amps, this can be a major issue and input clipping can occur if they are substantially below wide open and being driven hard to compensate.
02-01-2013 08:50 PM - edited 02-01-2013 08:51 PM
The original settings were 3.42v. I changed them to 5.75v to lower noise and bring the faders into a more workable range.
Ok, that's why you are having problems. You are overdriving the front end of the DSP (or input algorithems) and then using the bandpass gain as post makeup gain. You can pick up ~5dB of it right there by going back. I tend to stick with ~1.4V sensitivity to avoid these little quirks. This is what happens if you follow the stupid DriveRack gain structure advice in that manual too, helps them meet the noise spec. but it's not terribly useable.
5.75V (RMS) is ~8 volts peak and on a 12V rail (I am not positive but recall that the DSP ADC, DAC and analog stages use 5 volts and +/-12V with appropriate gain scaling of the input and output analog amps. The difference between 8V and 12V (less rail offset) is about 3dB, nowhere near adequate headroom for any post processing.
This is one of the things I had to redesign in the BBE unit that I tested here last year, had to decrease input sensitivity and increase the makeup gain to scale the ADC and DAC to real world (pro) levels. The DBX DR260 has jumpers built in to allow scaling as well.
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