Some thoughts on DSP, and an embarrassing confession

[Paul Carmody]

Re: Some thoughts on DSP, and an embarrassing confession

Both the analog and the digital are infinitely adjustable. Passive is doing the crossover post-amplifier (after the amplifier, between the amp and the speakers).

But that's the thing. Analog op-amps aren't infinitely adjustable. Compare the features and flexibility of that Ashly you linked to a DBX DriveRack (or, the DIY staple, the Behringer DCX2496).

[mattsk8]

Re: Some thoughts on DSP, and an embarrassing confession

But that's the thing. Analog op-amps aren't infinitely adjustable. Compare the features and flexibility of that Ashly you linked to a DBX DriveRack (or, the DIY staple, the Behringer DCX2496).

Having set up a large system using the Driverack PA+, a different system using a Op-amp based active crossover (albeit in a car stereo, it was a Audio Control), as well as the dial style in that Ashly (also in a car stereo), I understand. But not all active analog crossovers are op-amp based. Features and flexibility are nice, but I'm not talking about ease of adjustment. When all things are the same, I'm curious if the analog sounds better than the digital. De Focht said in his opinion the analog sounds better than the cheaper digitals, but I'm curious which price point. Is the MiniDSP one he considers cheaper?

[jonasz]

Re: Some thoughts on DSP, and an embarrassing confession

Just want to give some thoughts on this as at one time I spent a considerable amount of time and money trying to build a small speaker with good bass.

In short, if you can deal with the extra amps and cables, active is the way to go. There is so much unused potential in a speaker that can be brought out by using DSP. Let me explain.

Most people listen to music at moderate levels, but the drivers we use are capable of playing much louder. As long as you don't exceed the maximum SPL capabilities of the drivers you're using in your listening, then using DSP can let you get away with using much smaller speakers. For example, I have a speaker with dual 4'' woofers that I use in my kitchen. By using DSP, and applying a ~20dB boost (depending on the frequency) in the bass, it is capable of sounding like there is a very large subwoofer in the room when playing at normal volumes. It has shocked many people that a tiny, 0.15 cf speaker is putting out this kind of bass. Even though it can only sustain this much of a bass boost at a normal volume, that's pretty much all I need. If I wanted this time of bass performance without DSP, I would either need a *very* large floorstanding speaker or a subwoofer.

On the topic of crossovers, besides cost and more amplifiers, an active crossover is better than a passive one in *every* way.

- Higher efficiency because there are no losses from resistors.
- Lesser load on amplifiers because you don't have to worry about impedance and phase changes from using inductors and capacitors (which also improves sound quality).
- The ability to use steep slopes, which helps the transition between the crossover region, reduces distortion, and can better protect the tweeter.
- Micro adjustments to the frequency response of the driver to achieve closer to the perfect response
- And of course, way easier to design and experiment.

There are caveats. As Paul mentioned, it is not as simple as entering a crossover value and set slopes. You still need to listen. And be careful of over-EQ'ing speakers. While you can tinker and tinker and get a very flat on axis frequency response with DSP, it doesn't necessarily mean it'll sound good in a room. That's because when we're in a room, we hear the on axis and off axis reflected sound from the speaker, and that is determined by the directivity of the drivers. You can EQ the frequency response, but not the directivity because that's a property of a driver.

People shouldn't be ashamed of using EQ. Instead, it should be embraced. Smart DSP use will bring out the most out of a speaker in ways that passive crossovers simply can't. If you want the best speaker possible, active is the only way to go.

Thumbs up!

[Sydney]

Re: Some thoughts on DSP, and an embarrassing confession

... I understand. But not all active analog crossovers are op-amp based.

There are Tube Based Active Crossovers* as well. It really isn't about that however.

...but I'm curious which price point. Is the MiniDSP one he considers cheaper?

That market analysis is useful; realistically I don't expect a L.M.S. at the low end of the commercial market to be the equivalent of one used in a Broadcast or Recording Studio.

* A classic 1957 model

[natehansen66]

Re: Some thoughts on DSP, and an embarrassing confession

No sir, not merely by virtue of being converted to a digital representation.
I'm not sure I can provide a simple description of ALL the issues involved in converting an Analog signal to a PCM based digital stream* and then the conversion back to a usable Analog signal**.
There were a lot of technical hurdles that had to be overcome; A major one was the implementation of the error control coding utilizing the Reed Solomon code.
There are others - But this isn't a Digital design forum.

* http://www.ti.com/general/docs/lit/g...2&fileType=pdf
** http://www.ti.com/lit/an/sbaa055/sbaa055.pdf

Digital doesn't necessarily mean an external box with AD/DA. IMO the way to go is software based. Infinitely flexible with the horsepower to run any kind of IIR or FIR filter you can cook up. Of course a multichannel dac is needed, but you can then run from the dac straight to the amps. No AD middle man.....if the conversion is even audible. A pc based system opens up more possibilities than even the best external box, and we get to choose the dac we want.

[Sydney]

Re: Some thoughts on DSP, and an embarrassing confession

Digital doesn't necessarily mean an external box with AD/DA.....

Neither said not implied, particularly if the source is Already Digital ( of course that would exclude my old analog source material )

Of course a multichannel dac is needed

Yup ultimately a conversion back to Analog is necessary.
No speaker plays a digital bit stream after-all :p

[natehansen66]

Re: Some thoughts on DSP, and an embarrassing confession

Sydney - of course. You were talking about analog to digital and back though...unless my reading comprehension is failing me. Other posters seem to be mostly talking about these kinds of boxes as well so I thought I'd throw in my 2 cents.

Edit: I need to qualify my opinion and say that my sources are all digital - either on my hard drive or streaming sources so using a pc makes sense.

[Sydney]

Re: Some thoughts on DSP, and an embarrassing confession

Sydney - of course. You were talking about analog to digital and back though...unless my reading comprehension is failing me. Other posters seem to be mostly talking about these kinds of boxes as well so I thought I'd throw in my 2 cents.

Edit: I need to qualify my opinion and say that my sources are all digital - either on my hard drive or streaming sources so using a pc makes sense.

It's all good, I wasn't trying to limit to one approach but rather broadly explain the entire cycle from Analogy to digitization ( and back ).
I jumped on Cooledit and it's successors a long time ago, as recording music into a digital format has enormous advantages.
I also believed back when the first CD was introduced that the current RED Book standard was less than optimum, since then - doing my own recording experiments with higher sampling rates and bit depth has affirmed this.

[mattsk8]

Re: Some thoughts on DSP, and an embarrassing confession

The bottom line for me is that I'll probably go the MiniDSP route. I'm mainly curious if that's the most cost effective option, or if a Driverack would be better, or if even one of those analog Ashly crossovers would be better. I know the digital options offer a LOT more tunability with time alignment, PEQ, adjustable slopes, etc, but do they offer the same resolution and dynamic range of the analog options? Or is there a different digital option I should consider? I'd like something that's 2 channel in, 6 channel minimum out (for the option of a 2 or 3 way).

[Sydney]

Re: Some thoughts on DSP, and an embarrassing confession

Well I've heard analog devices that had less noise than others, and subjectively sounded better.

[natehansen66]

Re: Some thoughts on DSP, and an embarrassing confession

mattsk8 - from the standpoint of being able to dial the speaker in properly with the mini vs being limited to the fixed options on the Ashly I would say the mini would win hands down. Maybe I haven't looked at the right Ashly units.

[mattsk8]

Re: Some thoughts on DSP, and an embarrassing confession

mattsk8 - from the standpoint of being able to dial the speaker in properly with the mini vs being limited to the fixed options on the Ashly I would say the mini would win hands down. Maybe I haven't looked at the right Ashly units.

Unless you spend a lot, they pretty much are just analog active crossovers, and I think they're phasing those out because they only have the 1001 version available now which is only a 2 way, I'd need 2 of those to do an active 3 way. I am definitely leaning towards MiniDSP, but I'd love to know from someone with experience using that, verses a Driverack type, or maybe even something else. I definitely will be reading up on them