A DIY Line Mixer/Crossover/EQ/High Pass Filter

Passinwind · #1 03-11-2011, 03:24 PM

I guess this fits best in the Effects forum. I've been posting teasers around TB for a couple of months now, but I finally finished the build this morning.

I've been using DSP based speaker management/EFX mixer widgets in my bass rig for a few years now, but DIY ones seemed too expensive and convoluted until I came across this one. Now they are offering one in a case, and I expect them to do something similar to my take eventually too, especially if a few people drop the hint.

One very cool feature is the ability for the user to write their own filter definitions. You can just spec lots of cookbook stuff, throw it in a spreadsheet, and copy and paste biquad definitions straight into the Windows (or Mac) GUI. The programming interface is really simple and you can monitor the results in real time. I will post full performance test specs soon, but I can already say that audio quality is pretty darned good, and I may do a gig test this weekend just because I can.

Here's a pic of the front panel. The 4 pin connector is for the external power supply (12 volts DC at 150ma will do fine, you could use a wall wart), the USB port for programming the Mini DSP. On the back panel there will be four 1/4" TRS jacks, which can be used in a variety of ways. I only have two hooked up at the moment since that's all I really need for most of my intended uses.

Questions, comments, and general derision are welcome, as always.

cultrvultr · #2 03-11-2011, 04:10 PM

This is really really cool. Would love to see/hear your results!

4Mal · #3 03-11-2011, 04:16 PM

Where are you gigging this weekend ? We'll be out and about I'm sure...

dug dog · #4 03-11-2011, 05:23 PM

I've done some reading on these units based on the teasers you've posted earlier, but I was in a little over my head on their website.

Is there are an easy layman's explanation of what "biquad" means? I've googled it, but am still confused.

Thanks.

Passinwind · #5 03-11-2011, 05:43 PM

Quote:

Originally Posted by dug dog

I've done some reading on these units based on the teasers you've posted earlier, but I was in a little over my head on their website.

Is there are an easy layman's explanation of what "biquad" means? I've googled it, but am still confused.

Just think "state variable filter" as a building block. Now think up to 56 of those in whatever arrangement you can dream up.

Someone else already wrote the spreadsheet, so no scary math is really needed anyway. The app even graphs the expected response for you. But in any case, there's no need to use the advanced functions for most people, because the standard parametric and graphic filter options will already do a heck of a lot, and those just require selecting from a drop-down window, or moving virtual sliders. For some of us the ability to write our own filter definitions is pretty mind blowing though, especially given such a low price for the hardware.

knuckle_head · #6 03-11-2011, 08:01 PM

Hhmmmm.... reprogramable crossover. I'd spend near as much on a CBG.

Passinwind · #7 03-11-2011, 08:29 PM

Quote:

Originally Posted by knuckle_head

Hhmmmm.... reprogramable crossover. I'd spend near as much on a CBG.

This one can do Linkwitz Transforms and some other tricks that you'd love too Skip...

Foz · #8 03-12-2011, 06:53 AM

whadja pay for software... did you have buy in modules or can you buy it all in one go?

Passinwind · #9 03-12-2011, 11:53 AM

Quote:

Originally Posted by Foz

whadja pay for software... did you have buy in modules or can you buy it all in one go?

The plug-ins are ten bucks a shot, with download at time of payment. I bought three right off: mixer/graphic EQ, advanced 2-way stereo crossover, advanced 4-way mono crossover. Upgrades to the modules you own are free.

The crossover modules I bought include six bands of parametric EQ pre-crossover, and six more bands of PEQ per crossover band. You can get a module with 31 band graphic EQs instead, but you lose the advanced filter writing option then. There's also delay on each crossover band, for driver time alignment.

It's already pretty slick, but I'm working on the developers to add limiting and noise gating (downward expansion) eventually. They are open to writing a musical instrument-centric plug-in if enough people ask for that as well.

fdeck · #10 03-12-2011, 01:54 PM

Dude, this is cool. What's the processor platform? I've been interested in doing an open source DSP bass preamp project.

MX21 · #11 03-12-2011, 02:25 PM

Does this handle instrument level input or does it need a preamp?

Passinwind · #12 03-12-2011, 10:25 PM

Quote:

Originally Posted by fdeck

Dude, this is cool. What's the processor platform? I've been interested in doing an open source DSP bass preamp project.

AD 1701. There is lots of technical discussion on DIYAudio.com. MinDSP have their own support forum on their website as well.

Passinwind · #13 03-12-2011, 10:35 PM

Quote:

Originally Posted by MX21

Does this handle instrument level input or does it need a preamp?

I only use active basses, which will drive it directly OK but not optimally. I'll address that in my tests, which I'll try to get to this week. All my audio analysis hardware and software in on my old computer, which I need to set up again.

knuckle_head · #14 03-19-2011, 10:07 PM

. . . . and?!?

Did you gig with the box?

I see all sorts of win here. Is the USB port I/O - as in will it do A/D?

Passinwind · #15 04-01-2011, 09:11 AM

Quote:

Originally Posted by knuckle_head

. . . . and?!?

Did you gig with the box?

I see all sorts of win here. Is the USB port I/O - as in will it do A/D?

Still on hold, got sidetracked with a trip to pick up my new speaker cab.

The USB port is for control only, no audio goes through it. They do make ones with digital I/O though.

Touch · #16 04-01-2011, 06:54 PM

Quote:

Originally Posted by fdeck

Dude, this is cool. What's the processor platform? I've been interested in doing an open source DSP bass preamp project.

Wow... this combined with an upright-friendly FDeck HPF/pre?

Now that's change I can believe in!

Sign me up....for two!

rpsands · #17 04-07-2011, 03:11 PM

This will do what the FDeck HPF/pre will do already. You can do 12db/butterworth, lr, whatever.

No need for another box from what I can tell.

I have Putnam putting one of these in pedal form with a bypass (and master volume pot, input pad switch) for me. Will report out on how it works out. Intended use is as a butterworth HPF before my bass amp, but may try some more interesting stuff with it (like using it as an effect with drastic eq or similar).

It'd be pretty sweet if they offered an MI centric option with less eq, but a crossover and digital effects (e.g. chorus, reverb, etc).

Seems like you could accomplish a LOT with 4 outputs with different settings, and a channel switching box.

Passinwind · #18 04-07-2011, 04:40 PM

Quote:

Originally Posted by rpsands

It'd be pretty sweet if they offered an MI centric option with less eq, but a crossover and digital effects (e.g. chorus, reverb, etc).

Seems like you could accomplish a LOT with 4 outputs with different settings, and a channel switching box.

Compression/limiting would be the most likely next step, I think. If that were multiband it would be very cool. Time domain EFX would take a second processor, but I'd hit it...

My other DSP has preset switching and expression pedal support, which are extremely useful. Might be worth pitching that to MiniDSP.

I just spent a few hours dialing in some effects mixing patches. I'm jonesing for a gig where I can give this thing a real workout!

rpsands · #19 04-07-2011, 05:01 PM

This thing is making me want to pull the crossover out of my 15/6, replace my shuttle 9 with a power amp, and biamp. It's seriously pimpin'.

knuckle_head · #20 04-19-2011, 11:19 PM

I'll likely pull the trigger on one of these in the next week or two - balanced in, unbalanced in, 4 balanced outs. Potential 4 way configuration.

Pretty damn cool on spec.