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Author Topic: Ripple In DBX4800  (Read 5840 times)

Mac Kerr

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Re: Ripple In DBX4800
« Reply #10 on: August 23, 2013, 05:52:42 am »

My concern is that if I add delay for each bandpass individually for the reference measurement to get a flatter phase it changes the time relationship between the band passes.  If i remember correctly from when I took the measurements I did set the delay to the Low frequency transfer function, then left it in place for the HF transfer functions.

No it doesn't. It is only changing the measurement time so you get the correct phase display. You will then be able to see where the 2 phase plots are through the crossover, and if you need to change it, you add or subtract delay in the device without resetting the time in your measurement software.

Mac
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Doug Fowler

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Re: Ripple In DBX4800
« Reply #11 on: August 23, 2013, 12:07:49 pm »

No it doesn't. It is only changing the measurement time so you get the correct phase display. You will then be able to see where the 2 phase plots are through the crossover, and if you need to change it, you add or subtract delay in the device without resetting the time in your measurement software.

Mac

What Mac said. Also:

As someone else said, the phase response of an electronic measurement should be dead flat, except in the HF due to the sampling rate not offering a delay value that will completely flatten it.  You can get closer by using the highest sample rate available.

And, it doesn't look like a comb filter to me.  There is no complete cancellation at 1/2 f, with subsequent notches every f Hz above the first cancellation. 

Edit: of course the "complete cancellation" occurs only when the misaligned signals are equal in level.  Anything else changes the way it looks in a measurement.  Still, it doesn't look like a comb filter to me. 

Edit 2: and since it is not combining with anything, how could it be a comb filter?  It may be a jiggy 4800.
« Last Edit: August 23, 2013, 12:27:47 pm by Doug Fowler »
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Doug Fowler

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Re: Ripple In DBX4800
« Reply #12 on: August 23, 2013, 12:29:56 pm »

Are the two signals time aligned? Since the 4800 probably adds some propagation delay the result in the TF will be comb filtering, which I suspect is what your measurement shows.

Not accounting for device latency would obviously affect the phase response, but I would not expect it to affect the magnitude response, at least in SysTune.
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Mac Kerr

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Re: Ripple In DBX4800
« Reply #13 on: August 23, 2013, 02:15:41 pm »

Not accounting for device latency would obviously affect the phase response, but I would not expect it to affect the magnitude response, at least in SysTune.

It should not change the magnitude response in Smaart either.

Mac
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Malcolm Macgregor

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Re: Ripple In DBX4800
« Reply #14 on: August 25, 2013, 09:52:15 am »

If i understand correcty you want to copy the presets into your own unlocked preset file? first of i would start with measuring the device.

1. Use a flat preset (no changes to gain/delay/polarity/eq/phase/x-overs) and store a snapshot of it as reference

2. Open the preset you want to copy and write down the propogational delay for each of the outputs (from input to output of your fft I/O)

3. Now use the transfer function to store snapshots of each output and make sure you set the measurement delay correctly.

4. Create a new preset and start changing stuff output by output until they matchup with what you see in the previously recorded snapshots. (i usually start with gain, then delay, then x-overs, then eq, then allpass and tweak the bunch untill it's good.

For a transfer function to be of any use you really need to align the measurement signal to the reference signal, otherwise the phase display just isn't usable and you are missing vital info.

I hope this helps :)
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Re: Ripple In DBX4800
« Reply #14 on: August 25, 2013, 09:52:15 am »


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