[raindance]

I've been experimenting with using a mini DSP to remove a room mode that was dominating the sound in my system and here are my findings:
1. Correcting for the subwoofer only with the mini DSP out of the circuit to the Maggie's - this does not work as the miniDSP introduces a delay.
2. Correcting the full range signal before the power amp - this does not work as too much gain is lost by the mini DSP.
3. Correcting the full range signal between DAC and preamp - this gives promising results and allows me to run the sub crossed over at 40 Hz (Maggie 1.6's run full range). There's still a bit of gain loss, but the results in the bass are worthwhile. I'm getting the best measured results with REW that I've seen, ever.

My question for the group is: how do I set the gain structure properly on the miniDSP? I use a test CD (flat pink 4000) with a 0dB signal and set the level to -14 or so on the miniDSP, but I notice most CD's giving me quite a lot more level than this. I an sensing some minor distortion in vocals and a slightly artificial tone to cymbals. Any thoughts?

[raindance]

Note, when I say full range room correction I'm only applying a single parametric filter derived from REW. The reason I'm calling it full range is because I'm not separating out the subwoofer channel.

[Davey]

The miniDSP gadgets are unity gain.  You shouldn't lose any signal level by just passing through.
You neglect to mention which miniDSP unit you are using, so I can't answer your question specifically.

Also, you will find the delay (latency) of the units to be fairly low, but the preferred scheme would normally be to pass your entire chain through the unit (and have it do the crossover as well) so relative delay issues are eliminated.

Dave.

[raindance]

Apologies, I have the miniDSP 2x4. Input is set to 2V as it is being driven direct from a DAC. Output is 0.9V. So not unity gain.

[Davey]

Okay.
Yes, that would be the best setting for your example 3 above.
For example 2 you should set the jumpers to the 0.9v position to maintain unity gain and not experience the gain loss.  It's unlikely you would experience clipping in that instance.......depending upon power amplifier voltage gain.

I would opt for the placement between preamp and power amp and configure the other two outputs to feed your subwoofer.  That way you eliminate the latency issue and allow your sub-woofer crossover to work with the full-range signal.  Or you could disable your subwoofer crossover/EQ and let the miniDSP perform that function.  Other configuration options exist as well.

Make sense?

Dave.

[raindance]

Makes sense, however it does clip at 0.9V between pre and power before I get to full power - my amp requires 1.2V RMS for full output. If I connect it like in (3) at 0.9V it reads full scale and clips with the DAC at 0dB (obviously, as it is direct out from the DAC); however I can attenuate the DAC output and when I do this I seem to have to attenuate it quite far down to avoid clipping with wide dynamic swings, hence the loss.

I am passing the full signal through the unit to avoid the delay issue. Because these speakers drop like a stone below 40Hz, all I am doing is filling in the bottom below 40Hz. My room node is at 46Hz and is 12dB. So all I am doing is attenuating a fairly narrow band at 46Hz, I am not adding any boost within the DSP.

I am fairly happy with the way it is now, just wondering if there is a better way... Maybe the HD version of the 2x4 where I can achieve unity gain (2V in and 2V out)? I can't find much info on that product.

[Davey]

Your DAC must output 0dbFS voltage levels above 2.2VRMS???
If so, yes, you should attenuate it so as not exceed that level, otherwise you will clip the miniDSP A/D section with the jumpers in the 2VRMS position.

Generally, most people don't run their amps to full power with normal listening.  If you are doing that, I think you might need some more powerful amplifiers. 

Dave.

[raindance]

To follow up after much experimentation, the mini DSP severely curtails dynamics and renders the overall sound lifeless.

I've moved it back to subwoofer only duty. I wish there was an analog preamp available with a Quad-style tilt control and a single sweepable parametric filter to remove the primary room mode. That'd be useful.

And, by the way, my amp has plenty power for the Maggies. I only listen at about 93dB when I'm listening seriously.

[Davey]

To follow up after much experimentation, the mini DSP severely curtails dynamics and renders the overall sound lifeless.

Well, I don't really know what that means, from an objective standpoint.  Are you exceeding the hardware limitations of the unit or not?
If this is a gain structure issue, we can certainly solve it and/or understand it.  But if this is some sort of subjective evaluation, I can't help you. 

Cheers,

Dave.

[raindance]

Not a gain structure issue. More like a headroom issue. But these are my subjective findings, so YMMV.

I'm not looking for help any longer. Just hoping to help others who go down this path.

[raindance]

And yes, it is subjective. It's audio after all

[Davey]

A headroom issue IS a gain structure issue, hardware limitation, and not a subjective data point. 

Anyways, good luck.

Dave.

[limniscate]

I've tried a couple of times to integrate the DSPeaker 2.0 Anti-Mode with my 3.7i's and dual Rythmik F12G subs through my Aesthetix Calypso Signature.  So far I've only tried the DSPeaker on the subs, and it didn't seem to do much.  The before-and-after graphs seem to suggest that my room is already pretty flat.  I will try the DSPeaker between my DAC and pre at some point and will let you know my results.

[DTB300]

DSpeaker does a lot of smoothing if I remember right - making the curves not as choppy.

See if you can measure with another program and then seeing the graph in higher details.

I use the 8033 and it does a wonderful job on my JL subs.

IMO there are very few home rooms (not custom made) which measure flat from the get go.

[Barry100]

The DSPeaker 2.0 screen resolution due to the size is the problem, not smoothing.  Use it with a program like REW and you can actually see what it's doing and you will probably see that your room is not as flat before or after as it seems to appear.

I use DSP on the subs only with good results. Yes, there is some delay which is visible in REW but it's at such a low frequency, below 50 Hz, I can't hear it. Running it full range is the recommended option for time alignment but I do not care for the loss of transparency that imposes even with an upgraded bigger linear power supply.