How do I use the Pure Music crossover?

[Sparky W]

Hi Folks,

 

One feature of the Pure Music player that really intrigues me is the digital crossover. I would love to be able to use the crossover to split the signal between my mains and my subwoofers. But the Pure Music player wants a device that has four channels to do this. Obviously, my USB DAC only has two channels. So is there a way -- like some kind of software "device" -- that will let me send channels 1 and 2 to the USB DAC, and channels 3 and 4 to some other physical device, be it another USB DAC, the Mac's toslink, or even the Mac's internal DAC? Or am I missing some easier way to set this up?

 

Thanks,

Sparky

 

 

 

[untangle]

The easiest way to do this is a multi-channel DAC (or sound card).

 

You would then use PM's bus architecture to map out the channels, with appropriate crossover strategies on each.

 

Multiple devices are possible, but AFAIK much tougher.

 

If you are interested in pursuing this, you find multi-channel DACs (both USB and Firewire) in the 'pro sound' world.

 

Bob

 

 

[Sparky W]

Thanks, Bob, but I was hoping for a software solution that lets me split the signal. I'd like to keep my Ayre for the mains, and get something cheaper for the subs. It's going to be hard to find a pro DAC with the quality of the Ayre at that price point (if at all), but the subs are not nearly as sensitive so a modest DAC would be fine. But I don't know if the thing I'm looking for exists. The place to do it would probably be inside Pure Music, where the program could send the different channels to different devices, but that doesn't seem to exist. I was just hoping someone had confronted this or a similar issue in the past, or there was maybe a plugin to route different channels to different devices.

 

Ultimately, I'm trying to avoid an external crossover. My experience has been that they degrade the signal so much that I've been running crossoverless despite the difficulty in EQing.

 

Sparky

 

[untangle]

PM lets you split the signal, and hi/lo pass it (but not EQ it).

 

There are ways to take those signals and do interesting things with them - e.g., I use Jackrouter and Bidule.

 

But a multi-channel DAC is the most straightforward approach.

 

(BTW, I don't know what you mean by 'crossoverless design.')

 

Best,

 

Bob

 

 

[Sparky W]

Hi Bob,

 

I had a look at Jackrouter, and the manual directed me to Audio Midi Setup where you can create an "aggregate device" (i.e., a single virtual device that combines two or more physical devices). I haven't had time to experiment with it yet, but it looks promising. Have you tried this?

 

By crossoverless, I just mean that I'm currently running the full-range signal to both my mains and my subs. The subs have low-pass filters built in, so what I really need is a high-pass filter for the mains. But, as I said, my experience with line-level filters has been less than satisfying, so I was hoping to do it in the digital domain.

 

Sparky

 

[untangle]

Nope, haven't tried them. Let us know how it works out.

 

Bob

 

 

[Sparky W]

Okay, I gave it a brief try yesterday, and it seems to work. The Mac's Audio Midi Setup program makes it easy to create aggregated devices, and Pure Music recognizes them and the channels line up in order of the inputs on the collected devices. I was able to engage the crossover and send the low-pass output to one device and the high-pass to the other. Two issues I ran into:

 

1) There seems to be some weirdness when Pure Music changes sample rates on the fly. This didn't always work, but I didn't have time to fully scope out the problem or try many solutions. Obviously, when you treat two devices as one, there is the potential for miscommunication with one or the other.

 

2) The low-pass filter output of Pure Music seems to be *many* dBs lower than either the high-pass output or the unfiltered output. There is a trim setting on the filter, but even with it cranked up all the way (+12 dB) I could barely get sound out of either of the connected devices (routed to my subs). Again, more experimentation is in order, but this feels like a bug in Pure Music.

 

Hopefully I'll more time to play with it this weekend. But if anyone else takes a crack at this, I'd like to hear about your experience.

 

Sparky

 

[untangle]

Nice progress.

 

1. FWIW, I have found SR changes work pretty well in PM.

 

2. I have used PM's crossovers extensively, and never encountered a gain problem on the buses. Perhaps the output stage on your second device has a gain mismatch for your setup. Or you set crossover point to low. (I think that Rob's filters have a Q of 0.7-0.8.)

 

You can make bigger corrections on the buses by employing plugins. Lots of good-sounding ones are free/cheap. You can also EQ/xover via plugins on the buses.

 

Bob

 

[Sparky W]

Thanks for the input. I've found the sample rate changes to work well with my DAC, too (it's one of the things I really like about PM), but this aggregate device thing may be a bit more tricky. There are some settings to play with -- I'll let you know what I find.

 

Thanks for your input on the xover. It's good to know that the gain is correct. Now I can focus my efforts on getting the other bits to work right. In you experience, is there any degradation in the sound quality from using the high-pass filter at around 80 Hz?

 

The xover/EQ combo would be fantastic if I can get all these parts to play together -- I like to do room correction and it would be awesome to do it so far upstream while everything is still digital. About the buses on the plugins: I see "1, 2, 3, 4, All". Are 1, 2, 3, and 4 the individual channels? Thus if I want to EQ my low-pass channels, would I put a separate EQ plugin on each of #1 and #2, or can I combine channels 1 and 2 on a single bus and use a single EQ plugin?

 

Sparky

 

[ericuco]

I have been using the ARC System from IK Multimedia for about a month now and am pleased with the results. It is an AU plug-in for PM. It does not really allow much on the EQ side other than four different curves (e.g. HF rollover).

 

You will need an audio interface (e.g. TC Electronics Impact Twin) to do the initial setup. Basically connecting the microphone (supplied with ARC System) to your computer. Send me an e-mail if you decide to check it out and are in need of an audio interface.

 

 

 

[untangle]

In theory, SQ should increase - maybe dramatically - by do a HPF on your mains. After all, your amps and woofers will be relieved of their biggest burden: bass.

 

The "in theory" part comes from the challenge of getting the subs-mains integration right. This can be tough. Many folks never get it to their satisfaction. But it can be done.

 

The "1, 2, 3, ..." in PM refer to stereo buses, not individual channels. Of course, you can declare a bus "mono" if you like. This is helpful for use with a sub.

 

PM itself does not allow arbitrary mixing of channels. Perhaps it will in the future. But you can put multiple plugins on each (or all) stereo bus.

 

I use FabFilters for EQ (and often the crossovers themselves). Izotope is also excellent, and does much more than EQ.

 

Bob

 

 

[Sparky W]

So I managed to make this work. It's actually relatively straightforward: First one needs to create an aggregate device in the Audio Midi Setup. For the time being, I ran a stereo cable from my Mac's headphone out jack and ran the left and right wires out separately to my L and R subs. I'll probably get an outboard DAC soon, but this works for now. I made the aggregate device using Apple Built-in Audio (the headphone jack) as the first device, and my Ayre DAC as the second. The Ayre is the clock source, and the built-in is set to resample as necessary. The important thing when configuring this way is that both devices must have the same sample rate -- I set both to 96K and 2 chan/24 bit. I then selected this device as the default system output (note: I also turned the volume for the internal sound effects (alerts) down to zero). (The other option here is to select the Aggregate device from within PM.)

 

Once I fired up PM, I sent the LPF channels to 1R,2L and the HPF channels to 3R,4L. I confirmed that everything was working (at low volume) and sample rate changes were handled correctly. I got the subs and the mains running at about the same volume, then used the delay setting on the mains to get them into phase with the subs at the crossover frequency (80 Hz).

 

To do the room correction, I used Room EQ Wizard (REW). (Eric, ARC actually looks pretty good -- I'm going to do some more research on it. Thanks!) This was non-trivial because there are currently some problems with REW and Macs, the biggest of which is that you have to downgrade your version of Java to get it to work. This is not for the faint of heart, so I can't currently recommend REW for Mac users. Nevertheless, I had a working version, so I used it. It sends horrifying loud noises to my DAC, however, so I only ran it on the subs in isolation. I used Audio Hijack Pro (AHP) to catch the REW output before it got to the audio device. Within AHP, I used the Blue Cat Parametr'EQ to filter the output to get the response I wanted. When that was done, I installed the Blue Cat EQ onto the LPF bus within PM, and copied the settings that I'd used to get my desired response within REW and AHP. Kind of clunky, but it worked.

 

I did some listening today, and everything sounds pretty good. Once I've relaxed and listened for a bit, I'm going to try FabFilters and see if there are any audible differences relative to the PM and Blue Cat filters. And, as I said, I'll probably get another DAC (though I'm a little concerned about having two DACs on the same USB bus).

 

But this is pretty cool -- I now have my crossover and room correction all happening in the digital world, and my analog path has a minimum of components: DAC to amp to speakers. The resolution is pretty amazing, and the bass is tight and controlled and pitch-specific. My only complaint is that there is sometimes a little pop or click when jumping from one track to another. This may be an artifact of the EQ, but I'm not sure yet.

 

[untangle]

.

 

[Sparky W]

And thanks for your help.

 

A couple of new developments:

 

I forgot to mention last time that once I installed the EQ onto the LPF side of the processing chain, I needed to revise the delay of the mains to account for the processing lag of the EQ. It slows that leg of the processing by a few milliseconds.

 

Upon further listening, the Apple built-in DAC turned out to be unsatisfactory, leaving me with somewhat muddy bass. So I bought an HRT MusicStreamer II ($149 -- a bargain!) to handle the LPF side of things. I was somewhat concerned about having two USB DACs on the same bus (especially two async DACs), but everything seems to be working just fine. And my bass sounds better. Once it was connected, I had to reset the sub level and the delay. My earlier concerns about the LPF side being considerably lower in level appear unfounded.

 

I'm pleased with the quality of the HPF in PM. Aside from changing the frequency response, it is essentially inaudible. This is definitely the way to go for people who want to use a crossover in their system. I think it's a big selling point for PM -- PM should include a "How-To" on their site.

 

[renkinj]

I want to say thanks for this thread. I have been searching for a way to do this, not really understanding Bus architecture and you have the most coherent thread on the web. I was arriving at the aggregate device and just plugging in to try it, but now I see that it can work and have a path. Very appreciated. The PM instructions are a little vague.

A few simple questions, since I just found this and haven't tried anything (and with the 11 month old, it will happen at the pace of molasses in the antarctic...)yet.

1. with the two DAC set up, I assume they were USB DACs, did you just plug them into separate USB ports?

2. You mention setting both device outputs to the same bitrate, you used 24/96. Is there a problem with two devices that accept different bitrates? I have a DAC that accepts 24/192 and another two that accept 16/44. I was hoping to use the 24/192 for the full range and one of the others for the subs. Do you think there will be issues with that and PM will just downsample to the lowest common denominator?

 

Eventually to play!

Thanks again.

-j

 

[Sparky W]

Hi J, I'm glad you found the thread helpful. As to your questions:

 

1. Yes, I used two USB DACs, and just plugged them both into the USB bus on my Mac Mini. I was a little worried that this would overwork the USB bus, but I experienced no problems or dropouts. I will note, however, that this won't work with all USB DACs. If the DAC requires its own driver (like the Wyred 4 Sound DAC-2, for example), it will not work in an aggregate device. The solution in that case is to get a USB-to-SPDIF converter (that doesn't require a driver) and set up your aggregate device to use the converter.

 

2. The two devices must have the same max bit rate configured in Audio Midi Setup and/or Pure Music. I tried devices with two different bit rates, and it did not work. So you are limited to the maximum bit rate of your device with the lowest bit rate. The HRT Music Streamer can get you to 24/96 pretty cheaply, but I don't know how to get to 24/192 cheaply. Maybe someone else can suggest some options.

 

[renkinj]

Thank you for your answers. Sigh, it always is more complex than it seems. But it does give me yet more things to try, so the game goes on. I was planning to use a HiFace but it does require a driver, so that is out. I do have two other DACs, so I could try them.

 

Here is Channel D's response, do you have any clock issues?:

 

Hello,

 

You need a DAC / audio interface with more than two output channels. This can be 4 or more analog outs, or two or more analog plus a S/PDIF output (they have to appear to the Mac as four output channels). In the latter case, an outboard DAC could be connected to the S/PDIF. It is not practical to connect independent DACs and have this work properly, there is no way to synchronize the sample clocks of independent DACs. Pro audio DACs have this capability but then again they will also generally have more than two analog output channels. See our website for examples:

 

http://www.channld.com/support-soundcards.html

 

http://www.channld.com/computeraudio.html

 

A Mac Mini G4 may be a little under-powered for doing this, anyway. The Mini (and the laptops) used a low-power (and lower performance) variant of the G4 processor, so it is even less capable than a desktop G4 (tower or iMac).

 

Thank you,

 

Rob Robinson

 

Channel D Support

 

 

 

[Sparky W]

I didn't have any clock problems, but that doesn't mean they can't happen in some situations. Mr. Robinson is somewhat incorrect about the clock issue, however. When configuring an aggregate device, you can choose one of the devices to provide a master clock, and allow the aggregate device to resample for the other device(s) as necessary to maintain sync.

 

Given the usefulness of the PM crossover features, I'm a little surprised that the developers don't give the program the option to connect to two (or more) devices, and allow routing the various channels to those devices. This functionality exists in other software (Audio Hijack Pro, for example), so it's not technically impossible.

 

Seriously, what do they consider the market for this feature? Why did they go to all the trouble to include the crossovers and then limit their usage to the tiny percentage of audiophiles who have four-channel (or more) pro DACs?

 

[renkinj]

I agree. I found the explanations for setting up the digital XO so confusing because I was missing the obvious. I just assumed that the functionality to drive more than one device was there, when it is not.

I suppose I could just run it through Audio Hijack Pro. I have it and it inserts itself after everything else. I just am not sure if it would adversely effect the excellent processing of PureMusic. ie: is AHP 64 bit perfect?

My experience with AHP is that anything that boosts the signal, adds too much distortion.

Aside from this being a little frustrating, I love PM. Maybe I should point the developer to this thread...

 

[untangle]

Using PM/PV with multiple 2-channel DACs is a use case that even Apple is subtly moving away from. It's a kluge - esp since these DACs typically lack external clocking facilities. So getting them to work well almost requires an act of faith, especially if DSP is introduced.

 

But for those so inclined, the comments above contain most of the secret sauce.

 

But my advice is to try a multi-channel DAC. A Behringer or the like is very inexpensive and can be made to sound decent. Look at a Apogee Ensemble (less than $2K) for something really nice. I find the Prism Orpheus ($4.5K) that I use superior in every way to the Berkeley Alpha DAC that it replaced.

 

Given how inexpensive multi-channel DACs are and how klunky aggregate devices are, I think that it would be a waste of time for the developer of PM/PV to try to implement them internally.

 

IMO, there are many other exciting things (e.g., PEQ, saved xover configs, built-in measurements, room correction) that can be done to improve PM/PV and that should take priority.

 

Bob

 

[Sparky W]

I agree that aggregate devices are non-ideal, and a multi-channel DAC would be easier. But I think it is unrealistic for Channel D to think that a significant number of audiophiles are going to switch from their favorite audiophile DAC to a multi-channel pro DAC. It's much more likely that they'll just switch to another playback program that offers the performance and feature set they want. The crossovers in PM are a great idea (it puts the crossover where it should be in the system) and well implemented, but the fact that 99% of their potential customer base can't use the feature seems to be almost the opposite of a selling point -- it's a frustration. They advertise crossovers as a feature of the product, but unless you already have a multi-channel DAC, or can figure out the magic aggregate device incantations (which Channel D recommends against), then it's unusable.

 

Driver: "This car seems underpowered. I thought it had a V6."

Salesman: "Well, yes, it has six cylinders, but only four of them actually work unless you live in Portland..."

 

 

[untangle]

1. I don't even understand your automotive analogy.

 

2. As to the rest, we simply disagree.

 

3. I don't envy Rob (of channelD) in the face of requests of this sort, but I have have the utmost confidence in his judgement.

 

Cheers,

 

Bob

 

[Sparky W]

1. What's not to get? It's an advertised "feature" that seems to be a selling point, but upon closer examination is not useful to the overwhelming majority of the potential market.

 

2. I invite you to do a poll of audiophiles and look at the ratio of those using two-channel DACs to those using multi-channel DACs. Or have a look at the DACs for sale on Audiogon. Or leaf through the pages of Stereophile or TAS and compare the number of ads for two-channel vs. multi-channel DACs.

 

3. Why don't you envy him? He's running a business in a competitive industry and he has customers telling him about the features they'd like to see in his product. To the extent that he provides the features people want, he'll succeed. To the extent that someone else provides those features, they'll succeed at his expense. If I were him, I'd want the information, even if I couldn't always act on it.

 

[Lars]

"The crossovers in PM are a great idea (it puts the crossover where it should be in the system) and well implemented, but the fact that 99% of their potential customer base can't use the feature seems to be almost the opposite of a selling point -- it's a frustration. They advertise crossovers as a feature of the product, but unless you already have a multi-channel DAC, or can figure out the magic aggregate device incantations (which Channel D recommends against), then it's unusable."

 

If you don't want to invest in a multi-channel DAC that's your problem. Your complaints are getting old fast. Maybe you should try another program. Multi-channel dacs are very easy to find. Perhaps if you spent less time complaining and more time educating yourself, your posts would appear more impressive than they do now.

 

You had 15 days to determine if this program would work for you before purchasing it. Just because it doesn't do what YOU want it to do, doesn't invalidate the program for the rest of us.

 

[Sparky W]

"Perhaps if you spent less time complaining and more time educating yourself, your posts would appear more impressive than they do now."

 

Re education, see #2 in my previous post. You are invited to participate.

 

"Just because it doesn't do what YOU want it to do, doesn't invalidate the program for the rest of us."

 

Let me get this straight: Because you're happy with PM, I'm not allowed to discuss the features I'd like to see in the product, or the way the features are represented in the marketing material? And you speak for everyone? Interesting. That sort of zealotry is usually reserved for the fanbois on Apple forums.

 

BTW, what happened to the EQ that was supposed to be coming in 4Q2010? I guess I should shut up about that, too.