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Output summing after crossover 5 years 2 months ago #30972

  • bcodemz
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Hi,

I'd like to suggest a very easily implemented feature that can be incredibly useful - output summing for the miniDSP. What I'm thinking of is for a speaker that is a passive and active hybrid where the tweeter and midrange is passive but woofer is active. This will save cost so that a 3 way speaker only needs 2 channels of amplification, but still benefit from the active filtering and time alignment. This is also good for the woofer so that a 2 band (or more) multi-band compressor can be implemented.

All this requires is just to sum the output signals after the 4 crossover channels. Summing signals is extremely easily implemented. Plus, it is essentially just the routing matrix, so the GUI is already done as well. We just need another one near the end of the DSP block. It should take no DSP resources since summing is quite a simple operation.

I hope miniDSP can implement this. In fact, I want this feature so much I'd be willing to pay to expedite this feature or volunteer my time to implement it myself as I'm a programmer.

Thanks

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Last edit: by bcodemz.

Output summing after crossover 5 years 2 months ago #30973

  • dreite
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Summing of output channels is not required for the hybrid system configuration you outlined. The miniDSP unit functions as the woofer/(mid-tweet) crossover (before amps) and your high-level passive crossover the mid/tweet crossover (after amps.) No summing should be required. (However, I could be misunderstanding your objective.)

Regardless, if you feel the need to sum miniDSP output channels for whatever reason, simply "Y" them together with an appropriate adapter. The 600 ohm output resistance of all the miniDSP units supports this without risk of damage to the internals.

Dave.
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Output summing after crossover 5 years 2 months ago #30974

  • bcodemz
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Summing of output channels is not required for the hybrid system configuration you outlined. The miniDSP unit functions as the woofer/(mid-tweet) crossover (before amps) and your high-level passive crossover the mid/tweet crossover (after amps.) No summing should be required. (However, I could be misunderstanding your objective.)

Regardless, if you feel the need to sum miniDSP output channels for whatever reason, simply "Y" them together with an appropriate adapter. The 600 ohm output resistance of all the miniDSP units supports this without risk of damage to the internals.

Dave.


How would you pad the tweeter section with one crossover parametric EQ channel? I'm sure it is doable, but not easily. Plus, if you want to time align the mid and tweeter, you can't do that with just one. You need to use two, and then sum them up at the end.

A Y solution isn't the prettiest, especially if I want a multi-band compressor. For my 4 way speakers, I would need to buy a second miniDSP just to have a multi-band compressor and a bunch of Y adapters when it could be very very very easily done just by internally summing them before output.

I'm simply saying, miniDSP has done some incredible features. They gave us the compressor. Implementing a compressor is 100x harder than to implement signal summing. MiniDSP did 99% of the hard work of implementing the compressor, but in its current state it is only achieving about 1% of its potential usefulness. All they need to achieve the rest of the 99% of its usefulness is to do the last 1% of the work of adding output summation and it becomes hugely useful. Because of how ridiculous that is, I offered to do it for miniDSP for free even though as a programmer myself I earn a 6 figure salary to program. I have no problem doing 1% of the hard work to unlock 99% of its potential usefulness.

The current state of the compressor is pretty useless because all it does is physically protect the speaker at a huge expense to sound quality. Generally a compressor is used to compress the bass to prevent the woofer from bottoming out. Therefore, when the compressor is activated, the entire woofer band is compressed. If the speaker is 2 way, the tweeter is suddenly several dB louder than the woofer, which is a very bad sound. Even if the speaker is 3 way, you still lose all of the lower midrange too, making the speaker sound very thin.

So what needs to be done is

1. Either compress ALL channels. So if the compressor needs to compress the woofer channel by 3dB, it compresses every channel by 3dB so the overall volume is compressed by the compression magnitude (3dB) to avoid the huge tonal imbalance. That's a single band compressor, except in miniDSP's implementation it is a single band compressor on one output channel instead of the whole output.

2. Or the optimal solution: create a multi-band compressor where only the bass is compressed, leaving the tonal balance intact (except deep bass of course). That just requires output summation, which is very simple to do digitally. Even better if the 4 compressors (one for each channel) can be reassigned to one channel to make a 4 band compressor for one output. That would be truly useful.

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Last edit: by bcodemz.

Output summing after crossover 5 years 2 months ago #30977

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You're making this way more complicated than it needs to be. :)

A tweeter pad would implemented in your passive crossover.
Any relative mid/tweet phase-matching could be implemented in the passive crossover as well.

A "Y" solution is easily done and it is pretty.

Compression has nothing to do with any of this. Your initial post barely mentioned it, but now it seems to be your primary interest??
I have no interest in compression at all......I'm not sure why anyone would. Way too much program material already has too much embedded compression, so adding more is just crazy.

Dave.

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Output summing after crossover 5 years 2 months ago #30980

  • bcodemz
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You're making this way more complicated than it needs to be. :)

A tweeter pad would implemented in your passive crossover.
Any relative mid/tweet phase-matching could be implemented in the passive crossover as well.


One could, but you might as well go passive at that point. I prefer to have as few crossover components as possible to save cost and improve performance.

A "Y" solution is easily done and it is pretty.


I don't think you fully understand. Because of miniDSP's severe feature limitations, I have a pair of football sized speaker that requires not one, but *FOUR* miniDSP 2x4 HD's. Two of them are literally used only to implement a 2 band compressor through a Y solution because there is only 4 channels when I need 6 (one for tweeter, one for mid, two for front woofer, two for rear woofer). Because miniDSP couldn't internally Y a signal, I have to deal with spending $450 more on 2 more miniDSP's and 18 more pieces of cables (4 RCA inputs and 8 RCA for 8 outputs on 2 miniDSP's, 4 Y adapter, 2 power cable), not to mention having 2 more miniDSP boxes.

Surely you don't think having 18 more cables in the system is a pretty solution do you? Not just that, but for a tiny speaker too that I made for travel purposes. All of those mess and cost can be avoided with a simple internal output summation feature.

Compression has nothing to do with any of this. Your initial post barely mentioned it, but now it seems to be your primary interest??
I have no interest in compression at all......I'm not sure why anyone would. Way too much program material already has too much embedded compression, so adding more is just crazy.

Dave.


I don't think you understand what a compressor is used for in active speakers. It is very different from what a compressor is for music production. A compressor for active speakers is used to either protect the speaker from mechanical damage, and/or to limit distortion by preventing the output signal from exceeding the limitations of the speaker. It is a hugely useful tool to get much more usable bass out of a speaker/subwoofer without destroying the speaker's drivers or a speaker's headroom if bass boost is used.

I mentioned it because a simple feature will make a complicated feature from being useless to very useful.

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Last edit: by bcodemz.

Output summing after crossover 5 years 2 months ago #30991

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How would you pad the tweeter section with one crossover parametric EQ channel? I'm sure it is doable, but not easily. Plus, if you want to time align the mid and tweeter, you can't do that with just one. You need to use two, and then sum them up at the end.


Um... I don't believe what you are suggesting here actually works. If you want separate control over the response of two drivers, you do need to have two DSP channels and two amplifiers. If you sum the two DSP channels and feed them into one amplifier, each driver is getting the sum of the two DSP channels, multiplied by the transfer function of whatever passive components you have in front of it (i.e. not the same at all as the output from each DSP channel prior to summing.)

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Output summing after crossover 5 years 2 months ago #31055

I understand what you are asking. And I agree it would be useful.

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If we could sum the outputs internally then you could use multiple channels of dsp to create a Multiband compressor. It would be easy to implement and effective.

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This would be an excellent feature for maximising quality and achieving sensible speaker protection.

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Output summing after crossover 5 years 2 months ago #31130

  • devteam
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Pretty unique request and something we can put into the wishlist for review by the engineers. :-) We can't promise we can implement all the request we get.. Every new feature requires new firmware + DSP code + GUI testing + user manual update.. it's not always as simple as it sound.. :-) With this said, thanks for sharing new ideas.. we're always listening to see what's possible. :-)

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Output summing after crossover 5 months 2 weeks ago #58032

  • sgurdus
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Hey All, bubbling this back to the top to see if anything has been implemented in the 2x4 HD to enable limited, multiband compression capabilities. @bcodems suggestion to add a final summing option for outputs would effectively unlock multiband compressor capabilities since a compressor already exists for 4 output channels. I'd just want to sum two of the outputs into a single output for my woofer.
Very similar use case to Phil and bcodems. Smaller woofer that is EQ'd for for excellent, full range listening at low to medium volume. I'd like to be able to listen at louder volumes and only compress/limit the lowest frequencies (< 65hz) to preserve overall quality but with slightly less low end, to protect the speaker. My workaround, which required the 2x4 HD, is config presets. If the speaker will be used for higher volumes, I flip to the second config, which implements a more aggressive high pass filter to protect the woofer.
The other, less elegant solution is passive summing two of minidsp outputs (where a compressor was applied to the 40-65hz one).

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