Getting started in digital crossovers (using a Mac)

[untangle]

I get asked about this topic a lot, so here are the basics...

 

Digital crossovers are way cool. They enable many sonic benefits and, with some care, cost little. (Monetary costs as little as $500, but likely $1-2K, to start.)

 

For one thing, they enable bi-amping or tri-amping. Much has been written about why having a one-one relationship between amps and speaker drivers is ideal. Start with the single-driver literature.

 

Another huge benefit of digital crossovers is that they enable the use of steep slopes for the cutoff curves. This will likely result in a lowering of overall distortion levels in the final sound.

 

The most common use of active crossovers is to isolate the bass from the mids and trebles. This is logical, and a great place to start. In fact, I'd estimate that as much as 75% of the benefit of digital crossovers is from this key crossover point. A varient of this strategy is to use a digital crossover to accurately blend in a subwoofer with a pair of full-range channels.

 

If you want to pursue this technology, borrow or buy a multi-channel DAC. It is soooo much easier than trying to glue together multiple 2-ch DACs in software (aggregate devices, etc.), and will likely sound better too. Get one with a USB or Firewire interface, as this will eliminate lot's of hassles.

 

(I am partial to external audio interfaces. I like that they isolate the music-making gear from the noisy computer. But many reference rigs use Lynx or other sound cards.)

 

You can buy an inexpensive one first. Check out the Gearslutz forums. Look on the Sweetwater (or like) site. $400 or so is enough, but get a popular brand in case you want to trade up later.

 

If you like what you're hearing, you can then want to move up to a product that will stand toe-to-toe with audiophile 2-chan DAC's - a Metric Halo, Apogee, Prism (which I have), etc.

 

You'll need amplification and cables for your additional channels too. It's OK to just pull something out of the closet, or buy something on eBay. Again, you can upgade later if you like what you're hearing. The Linkwitz Lab web sites has lots of wisdom about active crossovers and amp/cable req'ts.

 

OK, those are the basics for source hardware and amps, now on to the speakers.

 

[untangle]

Oddly enough, your speakers may be the biggest barrier to active crossovers.

 

The reason is, to do this right, your existing crossover networks should be removed - if not physically, then at least electricly. That's the point. We want to remove everything that's between your amps and their respective driver...except your speaker wire of course.

 

In truth, you may get some benefits from wiring into your bi-wire posts (if your speaker has them) and overlaying steeper slopes digitally. But this approach would, at minimum, leave a lot of fidelity on the table.

 

I can't tell you how many high-end speakers that I've done a crossover-lobotomy on. But it's a lot. While the end result should be visually difficult to detect, this task is not for the meek.

 

So, if you don't want to do this, there's little reason to read on. For those adventurous souls that do, let's talk about software approaches....

 

[untangle]

Given my expertise (and the thread's title), this will focus on Mac's. But every approach and software component that I discuss here has a just-as-capable analog in the Windows world.

 

In order to implement digital crossovers in software, two things have to happen:

 

1. The signal must be split, with one copy destined to arrive at each amplifier; and

 

2. Digital filtering must be imposed on each channel, thereby effecting the crossover slope(s), be they low-pass, high-pass, or band-pass.

 

There are at least three ways to accomplish this on a Mac. Let's go through them:

 

I. IN THE MUSIC PLAYER ITSELF

 

I currently recommend that anyone playing music on Macintosh use ChannelD's Pure Music (PM)*. IMO, while other very capable players exist, none have the breadth of functionality that PM has. Nor is any other publisher keeping up with the pace-of-updates that ChannelD has kept up.

 

The other reason to use PM is that Rob Robinson of ChannelD has created a *reference quality* implementation of digital crossovers. I can make this claim because I have been using digital crossovers for years. I have tested at least 10 studio-level packages, several of which cost more than PM itself.

 

Rob's are more transparent.

 

If you've taken my advice and purchased a multi-channel DAC, you'll find that the nomenclature re signal routing (and crossovers) in the PM docs sounds a lot like the desciption of signal routing in your audio interface. There's a reason for that. It mimics an analog board, and that's what everybody on the pro side knows and likes.

 

The task here is relatively straightforward, as PM does all the work for you behind the scenes. You simply have to assign a software bus (stereo pair) to each bus on your DAC, and then define the frequency and slope of your crossover for that bus.

 

So, for example, you'd set PM's Bus #1 to feed Bus #1 on your DAC, and define a 4th-order lowpass filter at 100hz as the slope for that bus. (Your DAC would typically automatically map its Bus #1 to the first pair of RCA/XLR jacks - so you'd want to be sure that those jacks are connected to your bass amps in this example.)

 

And that's it - hit PLAY and rock on.

 

 

Now for the second method...

 

 

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II. IN A DIGITAL AUDIO WORKSTATION (DAW) USING PLUGINS

 

A DAW is a specialized tool that helps automate all the processes of a recording studio. Examples of popular DAWs are ProTools, Logic, and Cubase.

 

To automate a studio, a DAW must do more than just record mic feeds. It must also be able to play back tracks, splitand route them, and do filtering/EQ. So a DAW has all the capabilities necessary to implement digital crossovers.

 

But the DAW has big disadvantages for home playback: it's expensive, it's very complex, and it's not the greatest in managing a library with thousands of tracks.

 

It also usually requires external plugins to do the EQ (more on these in the next section).

 

For these reason, I do not recommend DAWs as playback software in the home.

 

 

III. USING STAND-ALONE ROUTING SOFTWARE AND PLUGINS

 

This approach is the most flexible of the three - you can use any player that you like, choose form 100's of plugins to tailor your crossovers and sound, and route and re-route to your heart's content.

 

It's also not very expensive.

 

But it's fairly complex to implement - about halfway between PM and a DAW.

 

If you learn nothing else from this diatribe, it's that three things are needed to implement digital crossovers: signal splitting, routing and signal filtering.

 

There are several tools out there that help with these tasks (e.g., Soundflower, Rewire, etc.), and I've tried most of them. But I've been particularly happy with a trio of them: Plogue Bidule (PB), Jackrouter (JR), and Fabfilters (FF).

 

PB, despite its zany name, is a very elegant tool for splitting audio signals and also hosting the signal filtering plugins. JR is audio middleware that connects your player (iTunes, Ayrewave, Amarra, etc.) and your DAC to PB. And FF are the best overall tools (other than PM) that I've found for implementing the crossover slopes. It's terrific.

 

(The Izotope Ozone DSP suite is also excellent.)

 

So Google them, download the free trials and get started!

 

Bob

 

* You could also use Pure Vinyl (PV). But ChannelD tends to release music playback improvements on PM first.

 

[untangle]

I can honestly say that DSP has changed the way that I interact with my system. I no longer have any desire to upgrade hardware components. If I want to change the sound, I do it digitally. I feel much more empowered.

 

But DSP and digital crossovers they are obviously not for everybody. the require nontrivial investments in time, money, and learning. They also are 180 degrees out from a less-is-more, don't-mess-with-my-signal-path philosophy. I get that.

 

But if I haven't scared you away and you'd like to pursue this tack, I'll try to answer any questions that you have in implementing DSP (including crossovers) on your Mac.

 

All the best,

 

Bob

 

 

[Nyal Mellor]

Hey Bob

 

Great write up. I am pretty sure that Jack limits you to 44.1 or 48 kHz sample rates (at least last time I looked). Soundflower can do any sample rate you like but you need to make modifications to the plist file to do so (last time I used it 96kHz was the max sample rate). The big advantage of PM you didn't mention is auto sample rate switching. Soundflower and Jack you have to set the sample rate on startup or in the audio midi controls.

 

I gave up on the audio routing thing, it was too much of a PITA to be worthwhile living with on a day to day basis. Starting the Jack server, then iTunes, blah blah.

 

IMO the ability to integrate an AU plugin into Pure Music is awesome and I was using FabFilter to do room correction prior to getting a DEQX. I watch with interest how Pure Music develops in this space.

 

I must admit that I have not tried the built in XO in Pure Music. I never had a 6 channel capable computer DAC to try this out. The new DEQX HDP-Express offers you crossover and 6 channel dac in a package priced less than most 6 channel dacs (with quite a bit of extra functionality as well). I have compared the DAC section of the more expensive HDP-3 against a Weiss DAC2 and at least in my system there is not a clear winner in terms of sound quality. I used the DAC2 to feed the HDP with a digital signal.

 

[untangle]

Jack will now do 192, as will Bidule and, of course, the plugins.

 

And yes, my Options #2 and #3 require dedication - lots of it! LOL.

 

Most folks seem to overly discount the sound quality of multi-channel pro DACs. But with a little care, you can get 8 great-sounding channels for the price of two 'audiophile' channels.

 

In truth, the easiest - but not most powerful or flexible - way to implement active crossovers is with a venerable Behringer DCX2496. Mod the output stage, and for

[Nyal Mellor]

Also there is the miniDSP, not sure if you have seen that. I have been very impressed by FabFilter, for the price it sounds awesome and the application design is off the charts. I'm not as keen on it in its 'linear phase' mode, I think Flux Epure wins on that one.

 

[hoka]

Great write-up!

 

My two cents:

I'm running "puremusic" and its crossover through a modified Griffin Firewave, (essentially a six channel firewire dac) I bought two of these on ebay for something like $20.

The Firewave is discontinued and requires some trickery to get working on OS X 10.6.4 but it is not difficult and can still be found on ebay for very little money!

 

Especially the modified version sound terrific even compared to expensive dacs and is a very cheap way to implement digital crossovers on the Mac.

 

 

[untangle]

minimum phase is your friend...

 

nice!

 

bob

 

 

[untangle]

This is exactly the way that I would suggest folks go - get an affordable (used) multichannel DAC and go from there.

 

I would, for example, pit a Behringer DAC + $100 in parts against much of the audiophile stuff out there (96k and blw for the Behr).

 

Thanks,

 

Bob

 

 

[hoka]

This is a request to generate a hardware list so we can choose our options:

 

So far known to work good on the mac:

 

Griffin Firewave

Edirol FA-66

 

Furthermore I would be interested in a discussion on the various filter characteristics build into "PureMusic"

At the moment I am trying to choose between the 24db/oct and 18db/oct options, input and evaluations are welcome!

 

[untangle]

Many multichannel pro audio interfaces* work well on the Mac. Chances are, if it has a firewire connection, it'll work well. (If it has USB, it prob will too - but less surety of that.)

 

The tougher question is, how does the unit sound?

 

Some units that I am familiar with that have sound quality commensurate with their price range:

 

RME Fireface 800 ($1700)

Apogee Ensemble ($2000)

Metric Halo Leo 8 ($3000, on sale)

Sonic Studio Amarra 4 ($4000)

Prism Orpheus ($4400)

 

IMO, the Apogee and the Metric Halo (at its sale price) represent the best value. I use Orpheus. (All prices from Vintage King.)

 

There are several decent options below $1000, but I lack enough experience with them to comment.

 

Bob

 

 

* These combine a data-level connection - USB or firewire - with the DAC. This is what I recommend. Many reasons.

 

 

[untangle]

A thorough discussion of this topic would fill pages.

 

I recommend trying two approaches:

 

1. Replicate the analog crossover (if known) digitally. It's usually easy to find this out from vendor specs or a phone call. If not, it can be reverse-engineered. Doing this, you can assess how your active/digital system compares to "stock." Shallow-order slopes also sound more open and dynamic - esp at low-to-moderate volume levels.

 

2. Implement an all-4th-order (24dB) solution. This leverages your newfound ability to do steep slopes for free. The 4th-order slope has inherent advantages. This approach will generally lower distortion and allow you to play at loud(er) volumes. Most times, I end up here.

 

Bob

 

[Student_Driver]

Have been spending some time thinking about implementing active DSP-Xover and had been intimidated by the apparent complexity of many of the solutions suggested on various forums. Your write up suggests that I might be able to implement with my PM 1.74/Mac Mini and a new multichannel DAC. I have several question but will focus on my two largest concerns regarding the Pro-Audio solutions.

 

1) How big a factor is the phono to rca adapter issue. Everything I've seen plug adapter-wise seems cheap. I'm usually reluctant to add any more signal connections, especially $1,99 radio shack type quality plugs into my signal path. Where/what/how are you adapting the phono plugs? Are there quality purveyors of adaptive line cables with phono on one end and RCA on the other?

 

2) The all-in-one solutions like the DEQX tout phase shift and time alignment as a key element. Are these adjustments possible with the Apogee, Metric Halo (Pro-Audio) solutions? Is this done in Pure Music with extensions?

 

Thanks, SD

 

[untangle]

1. The subject of RCA-to-XLR conversion is a deep and well-documented one. The three classes of solutions are: adaptors (a la Guitar Center), custom cables, and active solutions. Adaptors are the best way to start IMO, and - for me at least - custom cables (DIY) are the place to end. You will probably be surprised at how good these sound. Be cautious with active pro units, most of which are meant for sound-reinforcement applications.

 

2. You can implement polarity inversion and "time alignment" (delays) directly in PM. Beyond that, recognize that PM implements minimum-phase filters, not linear-phase filters, in its crossovers. This decision eliminates pre-ringing but introduces phase errors. Since the ear is quite sensitive to pre-ringing (ever hear a drum strike before it's stuck?) and insensitive to most phase issues (the room introduces a ton anyway), the PM filters sound natural to most listeners.

 

Through plugins, you can implement phase-linear systems of any ilk quite easily.

 

Bob

 

[Wavelength]

Gang,

 

my 2 cents...

 

In college I wrote a paper about this very subject. Some of you are laughing as you know I graduated in 1981. I had in my senior year converted the VAX 11/780 into both a FFT analyzer and a xover. As well as building a number of opamp and discrete based units.

 

bla bla bla...

 

Ok rule 1: Any xover point between 100-10KHz has to result in the use of the same amplifier to power the speaker in that range. This is a simple rule to understand. The differential sound between two amplifiers is greater than the differential sound of the speaker and therefore a requirement in the area in question.

 

Ok rule 2: Below even like 150Hz phase becomes a big issue. The use of line level input into the SUB per say will never match the speaker in the High Pass area because the High Pass speaker's impedance, phase and timing are all willy nilly because of the cabinet acting like a filter for the bass driver and it's contribution to the resonant frequency and inductance of the driver.

 

So really the only way to do a sub is with the connection to the sub's xover with the speaker level as seen by the speaker.

 

Now many will say that time delay and phase can be added to the digital xover... BUT!!!!! this is complex phase and timing in this region. Also note to anyone listening... midrange really starts at like 100Hz, not 1KHz (actually most is gone by then). Low E in open tuning on a guitar is about 80Hz, male vocals starts at 120Hz, heck middle C on the piano is what like 261Hz. Also sharp cutoff does not guarantee it is going to gell with the High Pass speaker.

 

Final point... this is big money, what do amplifiers cost? Really you would be better off buying a REL or some other sub with the use of your main speakers and just buy a better amplifier with the money you save.

 

Thanks

Gordon

 

[untangle]

Thanks, Gordon.

 

While you make some good points, let's please keep this thread on track as a DIY for those who want to implement an active xover in PM.

 

Perhaps another thread could be started to capture that pro's and con's of of active xovers, DSP, subs, etc.

 

With respect,

 

Bob

 

 

[hifitubes]

The new Antelope AD/DA looks interesting, then I could use the AD for Pure Vinyl when I get setup again.

 

Still, I have heard there can be impedance issues running floated pins on XLR when trying to go balanced/unbalanced.

 

I'm tryin to research if J. River has progressed enough to sync two zones perfectly yet so I can try two DACS and feed a full ranger and sub like a Hawthorne setup.

 

[Adrian]

Hello,

 

I am new to computeraudiophile and discovered this very interesting thread that has big relevance for my next audiophile project . I would like to embarque on a "active loaudspeaker" journey and purchased already the construction plans for building a Linkwitz LX521 multi-way active open baffle.

I intend to go the DSP way and use your recommandation regarding Pure Music. The key concern I have is regarding the DAC, no experience yet with pro DACs.

 

However, there is something fundamental that I don't understand:

 

When using a USB or similar interface from the Mac to the DAC (or sound card) and assuming Pure Music splits the frequency spectrum in Lows, Mids and Highs according to the x-over spec, then I assume that all these 3 digital streams flow over the USB interfaceat the same time, is this correct?

If yes, How does the DAC / sound card know how to discriminate and route the different streams to the 3 channels?!

 

Many thanks in advance!

 

Adrian

[bliss53]

Many multichannel pro audio interfaces* work well on the Mac. Chances are, if it has a firewire connection, it'll work well. (If it has USB, it prob will too - but less surety of that.)

 

The tougher question is, how does the unit sound?

 

Some units that I am familiar with that have sound quality commensurate with their price range:

 

RME Fireface 800 ($1700)

Apogee Ensemble ($2000)

Metric Halo Leo 8 ($3000, on sale)

Sonic Studio Amarra 4 ($4000)

Prism Orpheus ($4400)

 

IMO, the Apogee and the Metric Halo (at its sale price) represent the best value. I use Orpheus. (All prices from Vintage King.)

 

There are several decent options below $1000, but I lack enough experience with them to comment.

 

Bob

 

 

* These combine a data-level connection - USB or firewire - with the DAC. This is what I recommend. Many reasons.

 

I have a Lynx Hilo ($2,400) and the TC Electronic Impact Twin ($400). Based on 2 channel listening the Impact Twin is a great value. I am about to try tri-amping with Pure Music so I will report on my experience. Thanks for the write up Bob. It was helpful.

[Sam Leach]

"But the DAW has big disadvantages for home playback: it's expensive, it's very complex, and it's not the greatest in managing a library with thousands of tracks."

 

Hi Bob,

 

I know this is going back some years for you now! But this post is very helpful!!

 

I am just beginning to change my system around and I am going to be using digital crossovers: the speakers I have are Martion Bullfrogs, and they are "active" versions. In practice this means they do not have crossovers on board, but shipped with some fairly prosaic electronics to drive them: a minidsp and a fairly modest modified pro-amplifier. I have some decent amps I can hook up and I have bought a Lynx Hilo to work as the multichannel DAC.

 

Anyway...on the subject of digital crossovers: I like to play some music from soundcloud and other streaming services from time to time when I am searching out new music. Puremusic seems like a great system, but if I use it to implement my crossover, I don't think I will be able to play my streaming media with it, will I?

 

So I am looking at your Jackrouter/Pogue Bidule option, I think...

 

And do you have any more wisdom acquired in the subsequent years that you could share?

 

Thanks

Sam

[Brian Parker]

"But the DAW has big disadvantages for home playback: it's expensive, it's very complex, and it's not the greatest in managing a library with thousands of tracks."

 

Hi Bob,

 

I know this is going back some years for you now! But this post is very helpful!!

 

I am just beginning to change my system around and I am going to be using digital crossovers: the speakers I have are Martion Bullfrogs, and they are "active" versions. In practice this means they do not have crossovers on board, but shipped with some fairly prosaic electronics to drive them: a minidsp and a fairly modest modified pro-amplifier. I have some decent amps I can hook up and I have bought a Lynx Hilo to work as the multichannel DAC.

 

Anyway...on the subject of digital crossovers: I like to play some music from soundcloud and other streaming services from time to time when I am searching out new music. Puremusic seems like a great system, but if I use it to implement my crossover, I don't think I will be able to play my streaming media with it, will I?

 

So I am looking at your Jackrouter/Pogue Bidule option, I think...

 

And do you have any more wisdom acquired in the subsequent years that you could share?

 

Thanks

Sam

 

bump

[InfernoSTi]

I think this is a big advantage of direct digital...perhaps DigiPete or someone can comment? I think there are other digital crossover threads, too (perhaps buried in room correction threads?). This is very interesting stuff...

[lamode]

Many multichannel pro audio interfaces* work well on the Mac. Chances are, if it has a firewire connection, it'll work well. (If it has USB, it prob will too - but less surety of that.)

 

The tougher question is, how does the unit sound?

 

Some units that I am familiar with that have sound quality commensurate with their price range:

 

RME Fireface 800 ($1700)

Apogee Ensemble ($2000)

Metric Halo Leo 8 ($3000, on sale)

Sonic Studio Amarra 4 ($4000)

Prism Orpheus ($4400)

 

IMO, the Apogee and the Metric Halo (at its sale price) represent the best value. I use Orpheus. (All prices from Vintage King.)

 

There are several decent options below $1000, but I lack enough experience with them to comment.

 

Bob

 

 

* These combine a data-level connection - USB or firewire - with the DAC. This is what I recommend. Many reasons.

 

I'm interested in building my next system around a digital XO (probably bi-amped) but at these prices, I could get a better upgrade to the sound by simply adding $5K to my speaker budget in the first place. ($3K for interface, $2K for second amp)

 

But... that list is 4 years old now and things can change quickly in the digital world. How does the list look now?

There are some high-end 5.1 and 7.1 sound cards which might be worth trying, and for very little money, but probably PC only.

 

Is PM still the only player option? How about an AU plugin which could be used in a variety of players? Does that exist?