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DSP speaker crossover

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natehansen66:
OK, here's a reply I had for someone on another forum asking how to setup MC for an active speaker system:


--- Quote ---The main thing in doing a crossover with J River is getting the channels routed properly. Go to the DSP Studio-Output Format. Select the number of channels that you need from the drop-down menu on the right. It sounds like you're doing 2-ways so 4 channels will work. Make sure "Mixing" is set to no up mixing or down mixing.

One thing you need to understand, is that the different sub-menus of the DSP Studio that are listed on the left can be moved up and down in order (except for Output Format and Volume Leveling, these are locked). This is important because these are processed in order from top to bottom. If it isn't already third from the top, move the Parametric Equalizer up under Volume Leveling. Then in the PEQ click Commands/Add/Mix Channels. This will allow you to tell JR which channel goes where, because until you tell it otherwise it only sends the signal to L & R. After you click "Mix Channels" choose Left for the "Source", and Center for the "Destination." For "Mode" select Copy. This will copy the Left signal to the Center channel. Now click "Commands" and add another mix channel filter, you'll see another one added to the list of filters. For this one choose Right for the "Source" and Subwoofer for the "Destination." Now you have 2 channels with a left signal and 2 with a right. I'd use the Left channel for your tweeter and the Center channel for your woofer. Your Right channel would then be your other tweeter and the Sub channel would be for your other woofer.

From there you can use whatever filters you like from the Commands button to do your eq/crossover, making sure you assign the filters to the correct channel. The filter list works like the DSP Studio sub menus in that it works in order from top down. You can drag filters up and down in the list. Make sure that any eq/crossover filters are below the channel mix filters in the list. Any filters you put ahead of the channel mix filters will be done globally to the L & R channels, which will affect all 4 channels.
--- End quote ---

Use ASIO, and set the AF12 to "Surround" in its settings.

The routing is as follows:

MC   AF12
Left         1
Right       2
Center     3
Sub         4
SL           7
SR           8
RL           5
RR           6
User 1      9
User 2      10

I've never tried to use the 11th and 12th channels..........

Edit: I was whining about the Wiki? A search for "Parametric Equalizer" brings up a link to the thread with all this info  ::)

CraigNZ:
Works perfectly!  Thanks heaps.

I ended up leaving the surround channels as is and 'copied' LEFT and RIGHT channels to 9 and 10.  I will put HPF outputs as LEFT and RIGHT and LPF outputs as 9 and 10.

I tested the configuration using the JRiver test tones and monitoring the AF12 front indicators.

CraigNZ:
Using REW I have now confirmed that cascading two LPF or HPF does indeed drop the amplitude of the signal by -6db at the crossover point, simulating a L-R 24dB filter.  Now how do I check the phase between the two channels?  In theory the L-R filter will generate a 360 degree phase difference between the two filters (LPF and HPF), but is there a way to check that using REW?  Or has someone already confirmed this on here?

My test environment is to take the output of the channel in test (on AF12) and patch it to Input 1, which REW then monitors.  This insures that REW is measuring the output of the soundcard channels rather than upstream somewhere.  For example, for LEFT channel I have HPF output going to Channel 1 and the LPF output going to Channel 9.  To look at either the LPF output or HPF output I then use a TRS patch cable and connect Input 1 to either Output 1 or Output 9.

I would also recommend that we setup a DSP section on the forum because I can see this is going to become a very popular topic and very advanced.  It would be convenient to have all the DSP related topics in one area.

natehansen66:
You can do a dual channel measurement in REW to account for the latency of the measurement system if you want to look at phase. I can go into detail later if you'd like.

natehansen66:
Do you have a measurement mic? Looking at how the filters work at the electrical level is good, but you need to see how they interact with the acoustic output of the drivers to do it right. Unless you've got flat response on either side of the xover freq for several octaves you'll never hit a theoretical transfer function without measurement.

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