emu's patchmix dsp demystified

Published in SOS November 2005Printer-friendly version

Emu's Patchmix DSP Demystified...Technique

Technique : Recording / Mixing

We demystify the powerful internal routing and

mixing engine within Emu's recent popular range of

computer audio interfaces.

Martin Walker

The new range of Emu soundcards (1820M, 1820, 1212M,0404, and by the time you read this the 1616M as well) hasbeen selling like hot cakes, but many PC musicians find variousaspects of their associated Patchmix DSP utility difficult tocomprehend. It's not that the mixer is difficult to use; more that itoffers so many possible options that it can be difficult for thenewcomer to perform even basic tasks.

The Patchmix DSP mixer design is based on a conventional analogue mixing console, with theinput channels on the left-hand side, main and monitor mix output channels on the right. Thesevarious input and output channels have inserts, aux sends, pan and level controls, mute andsolo buttons, and so on, which generally makes perfect sense to most musicians who havebeen brought up with such mixers. However, there's a new breed of musicians who have onlyreally experienced the virtual world of the software studio, and it's hardly surprising that theyfind this layout unfamiliar. So in this workshop I'll be covering the basic principles behindPatchmix and then explaining some of the more arcane operations.

Basic Mixer Features

Let's start by quickly recapping on the basic functions available. Emu have made the PatchmixDSP mixer totally configurable, so you can have as many input channels as you need, up to amaximum of sixteen in stereo — you can add extra channels at any time. I normally opt for thesimplest arrangement for the task in hand in order to keep the mixer smaller on screen so thatit doesn't get in the way of other windows. A label showing the channel type appears at the topof the strip, and you can drag and drop the input channels into any order in your mixer design.

Some people get confused by the fact that every channel strip is labelled as Input, whether it'sbeing used to listen to a physical signal source plugged into one of the Emu input sockets, orcarrying a playback output signal from your audio application. However, in both cases you'resending these signals through the mixer either to monitor via one or more of the physicaloutput sockets, or to route them elsewhere using sends.

For each mixer channel you create using the New Strip function you must choose one of theavailable input options from a selection of Physical Sources comprising whatever input socketsyour particular Emu card has on offer, such as the mono mic/line inputs, stereo line inputs,S/PDIF input, or ADAT inputs. Alternatively, you can select one of the Host Sources — eitherone of the sixteen stereo ASIO Output Sources (carrying stereo playback signals from youraudio application), or the single stereo Windows Source for playback when you're using anapplication with Direct Sound or MME-WDM drivers and when playing back Windows sounds.

Below each channel strip's label is a set of six Insert slots, into which you can insert a varietyof different objects (more on these later on). Next are the pan controls, followed by two auxsends, which can be used to add variable amounts of Emu's DSP effects, such as reverb orchorus, to all the channels globally. The bottom section of the channel strip comprises a striplevel fader with associated text box so that you can directly enter a suitable level in decibels.The Mute button removes the output of that channel from the mix, while Solo allows you tohear it in isolation. Finally, at the bottom there's a 'scribble strip' where you can enter adescriptive name for the channel.

In this article:Basic Mixer

FeaturesWhat's So

Different AboutPatchmix DSP?

Problem-solvingTips

Sessions &Sample Rates

RecordingOptions

On-line HelpDSP Effects

RoutingPatchmix DSP

TipsMore Complex

Signal Paths

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Emu's Patchmix DSP Demystified... http://www.soundonsound.com/sos/nov05/articles/emupatchmix.htm

1 de 6 31/05/2013 19:10

To play back stereosounds from ASIOand MME-WDMapplications, this isall you need in thePatchmix DSPmixer. Notice howthe mixer output hasbeen routed to thephysical outputsocket named DockOut 4 so that you

What's So Different About Patchmix DSP?

Some audio interfaces simply hard-wire the various driver playback channels to thephysical output sockets (for example, ASIO 1/2 playback comes out of Out 1/2, ASIO 3/4from Out 3/4, and so on), and hard-wire the various physical input sockets to the variousdriver inputs (In 1/2 to ASIO In 1/2, and so on) for recording. This is the way a lot ofmusicians want to work anyway. Those interfaces offering direct or 'zero latency'monitoring will also provide the option of routing physical input sockets direct to physicaloutput sockets, so you can monitor the incoming signals during recording without anysoftware delays.

The next step up in versatility is providing a dedicated hardware monitor mixer on theinterface, so that you can mix together various live input signals and playback signalsfrom your sequencer, and either use this combined stereo signal to feed a physical output— a monitor mix on headphones for performers during the recording phase, for instance— or send it to a driver input so you can record lots of signals onto one stereo track ofyour sequencer. This is the approach used by manufacturers such as Edirol, M Audio, andTerratec. In these cases, however, you can still completely bypass and ignore the monitormixer by choosing the direct routing options for both physical inputs and outputs, asbefore.

Emu have taken rather a different graphical approach, and at first it appears that everysignal must be routed through the entirety of the Patchmix DSP mixer. The secret is that,while much of the mixer is indeed dedicated to creating a monitor mix that appears onboth the Main and Monitor outputs, you can also use the Insert slots in each channel toroute input signals directly to your sequencer, or output signals directly to physical outputsockets, as with any other audio interface. If this is all you want to do, a useful mental trickis simply to ignore all the Patchmix DSP controls below the Insert slots, as well as themixer's entire output section (see screenshot). It may also be useful to activate the Mutebuttons for these channels, so you remember that you're not listening to them through themonitor mixer but by directly routing them elsewhere.

Problem-solving Tips

One of the first difficulties experienced by many users is simply getting a sound out of themixer when attempting to play back WAV files or soft-synth sounds. The easiest emergencyadvice is to load a New Session (configuration of input and output channels and routing), usingthe Save As option that pops up to preserve any of your own existing settings for another time,and then to choose a template from the thirty or so on offer. This will reset everything tosuitable defaults, and in many cases your sound will return immediately. If you're using the1820 or 1820M, though, many of the templates assume that you'll be using the Audiodockoutputs 4L and 4R as Monitor outputs, so make sure these are what your amp/speakers areplugged into as well. If you're using the MME-WDM drivers with an application like SteinbergWavelab, your output signal will be passing through the input channel strip marked Wave L/R,while ASIO applications will probably default to ASIO Out 1/2.

At this point, let me introduce you to the single most helpful hint of all.To help sort out Patchmix DSP routing problems, always put a PeakMeter in the topmost slot of each mixer channel by right-clicking on theslot and selecting 'Insert Peak Meter'. This will show you where youhave active signals, even if you can't hear them due to some routingproblem.

The easiest output routing is through the monitor mixer, the controls forwhich are on the right-hand side of the mixer window: master controlsfor the main and monitor outputs, read-outs of current sample rate andclock source, plus a 'TV window' above that which displays extracontext-sensitive controls. You'll probably already see the Main Mixoutput meter twitching in time with your signal (if not, you've eitherpulled down the channel fader, activated its Mute button, or have someother Insert blocking the signal). Now all you need to do is make surethe output of the mixer is routed to the output socket that you'relistening on.

Click on the Outputs button above the 'TV window', and then on the boxmarked Physical — this will display vertical strips of red and greenboxes on the left, and a list of possible physical output sockets on theright, depending on the Emu card you're using. To connect the Main orMonitor output to your choice of output socket just click on the red orgreen box adjacent to it — you can send either of these signals to asmany simultaneous physical outputs as you wish. The monitor output


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hear the signalsfrom both channelssimultaneously).

carries an identical signal, but with separate volume, balance, and mutecontrols, which is a handy when you're wanting to work onheadphones.

If you want a more direct signal path without all the extra options of themonitor mixer, just activate the Mute button of the channel in question, right-click on an emptyInsert slot, and select Insert Send (Output To ASIO/WAVE Or Physical Out). When the NewSend Insert window appears, choose the desired physical output from the drop-down list (forexample, PCI Card S/PDIF L/R, PCI Card ADAT Out 3/4, or Dock Out 3L/3R). This is theapproach to use when (for instance) you want to send eight ASIO channels from Cubase SXto individual ADAT outputs — just create one stereo send for each of the four ASIO channelpairs.

Sessions & Sample Rates

You can save your own different configurations of the Patchmix DSP mixer (known asSessions), for use with different applications and in different scenarios. For example, I'vecreated some that incorporate the settings needed to transfer digitally to and from myportable DAT recorder. Depending on the interface model, Emu also provide a set ofabout thirty default Sessions covering multitrack recording and playback, ADAT transfer,guitar tuning, and a special one for use with the Emulator X Studio sampler if you havethat as well.

One important thing to remember is that the Patchmix DSPmixer offers DSP effects that only run at either 44.1kHz or48kHz sample rates. There are also several restrictions on thedigital ADAT and S/PDIF connections beyond 48kHz. Becauseof these various fundamental internal changes, it's impossible tolet software applications switch sample rates for youautomatically behind the scenes. So, although with most audiointerfaces you can load and play WAV files at almost anysample rate, the interface automatically accommodating you bychanging its current rate behind the scenes, the Emu range(along with various others including Edirol's UA and FA ranges)require you to set the appropriate sample rate manually. If youtry to play back or record at a different rate from the one currently set in the hardware,you'll either get an error message or just silence.

To set your preferred sample rate directly from the Patchmix DSP utility by choosing oneof the New Sessions on offer — when you click on the New Sessions button on the mixertoolbar a dialogue screen will be launched with three main tabbed pages. If you chooseone of the supplied sessions on the 44k/48k page you can decide which of the twosample rates you want on the following page, while the sessions on the 96k and 192kpages are fixed at these sample rates, and provide default sessions with no effectsprocessing.

The eagle-eyed among you may have noticed that 22kHz, 88.2kHz, and 176kHz haven'tbeen mentioned. This is because the Emu range doesn't currently support these samplerates at all. Although this may prove frustrating to some users, there is one advantage innot supporting 22kHz. While ASIO drivers won't convert between sample rates behind thescenes, MME-WDM ones normally will, and if you play a 22kHz system audio file, yoursequencer project may end up having its sample rate changed until the next boot. WithEmu's approach, the 22kHz file will simply be ignored, leaving your sequencer playbackintact.

Recording Options

Next, let's say you want to record a stereo signal through a couple of the line input socketsand therefore want to route its signal to your audio application. If your chosen line input pair(Dock In 1L/1R for instance) isn't already displayed in the Patchmix DSP mixer as a stereochannel strip you first need to use the Append New Strip option to add it to the mixer.

Then you have to route it to the audio application. Right-click on one of its Insert slots, selectthe Insert Send (Output To ASIO/WAVE Or Physical Out) option, and then choose where youwant to send it to, for example HOST ASIO In 1/2 for any application using ASIO drivers (suchas Cubase or Sonar), or HOST WAVE L/R if you're sending it to an application usingMME-WDM drivers. If at any time you want to refer back to this routing, just click on the Insertin question, and the connection you made will appear in the 'TV window'.

With the current Patchmix DSP version, each of the mono Dock Mic/Line inputs of the1820/1820M models can only be routed to a stereo destination. So, although you could forinstance route mono input Mic/Line A to the ASIO 1/2 inputs of your sequencer and pan it hard


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Here's a setup thatwill convert twomono mic inputsinto a single stereoinput in yoursequencer.

Using thischannel stripsetup youcould recorda guitar bothclean andwith externalhardwareeffects ontoseparatesequencer

trackssimultaneously.

left so it only appears on the ASIO 1 input as a mono source, you stillwouldn't be able to use ASIO 2 for a second mono input channel, sincethe ASIO 1/2 pair is now greyed out as an option. This can befrustrating if you're wanting to record with stereo mic pairs, or if you'dlike to use the two inputs as extra stereo line inputs.

However, there's a way round this limitation, allowing you to send thetwo channel strips into your sequencer as a single stereo input. First,create the two channel strips for Mic/Line A and Mic/Line B, but makingsure that you tick the Aux Send Pre-fader option in the New Mixer Stripdialogue. Next, pan the first strip hard left, and the second hard right,and set each of the Aux 1 send controls to 0dB — this results in the twomono signals being sent to the stereo Aux 1 bus.

Now mute the two channel strips (the pre-fader option we used earlierprevents the Aux 1 signals disappearing at this point), and move to theAux Effects section of the mixer. Set the master Aux 1 Send to 0dB, butthe master Aux 1 Return to its minimum -132dB setting. The final stepis to right-click on the first master Aux 1 Insert , and select Insert Send(Output To ASIO/WAVE Or Physical Out). Choose a stereo HOST ASIO destination, and ourtwo mono channel-strip signals will end up in the sequencer as a stereo pair. Once you're surethis routing is working, save the Session for later use.

On-line Help

You'll find lots of posts about Emu soundcards and theEmulator X soft sampler in the SOS Web Forum, but thereare other resources that cater more specifically forEmu-owning musicians. The most popular are the unofficialEmu forums at www.productionforums.com/emu/default.asp, which cover all of Emu's interfaces andsoftware, as well as dealing with integrating these productsinto all the major sequencers. You'll also find that Emu staffregularly put in an appearance with 'official' answers,despite the fact that these forums are not run by Emu themselves.

If your Emu soundcard is one of the ones bundled with Emu's Emulator X sampler, I'vealso discovered two more web sites with useful information. Emus On Acid(www.emusonacid.co.uk/forum) is primarily a forum dedicated to Emu hardware samplers,but does host one for the Emulator X as well, as do the Studio-central Community Forums(http://studio-central.com/phpbb).

DSP Effects Routing

The bundled effects are roughly equivalent in quality to a mid-range hardware unit, and runinternally at 32-bit resolution and 44.1kHz or 48kHz sample rates. As with an analogue mixingdesk, the two aux sends come after all the Inserts, and are therefore ideal for adding effectsfor monitoring purposes (such as reverb during vocal recordings) when you want therecordings themselves totally dry to retain more flexibility during mixdown. This is where thefunctions of the Patchmix DSP mixer start to outstrip most of the competition, since you're notusing any of your PC's native processing power to run the effects — you just left-click on theFX button to launch the Effects Palette window, and then drag and drop the desired effectacross to an empty Insert slot in the appropriate channel.

With earlier versions of the Patchmix DSP mixer it was confusing trying toadd different DSP effects to multiple playback channels — the processinvolved creating a number of stereo output buses in your chosenmultitrack audio application, routing each one to a different ASIO output,creating the appropriate ASIO channel strips in the Emu mixer, adding theeffects as just described, and then routing the treated signals to physicaloutputs or back into the sequencer application. Thankfully version 1.6made life far easier, and you can now access the various Emu DSP effectsdirectly from within your chosen sequencer application as ASIO plug-ins.Just choose the plug-in marked Emu Power FX, then drag and drop one ofthe available DSP effects into an Insert slot in the Emu Power FX plug-inwindow. Some musicians have apparently experienced Emu Power FXsettings disappearing when reloading Cubase songs, and a few havesuffered crackling and synchronisation problems with some hostapplications. If this turns out to be a problem for you, then remember thatthere are also plenty of ways that you can use the DSP effects within the Patchmix DSP mixer.


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For instance, why not add compression, distortion, or a complete chain of effects, to a guitarinput in real time? The channel Inserts operate on the signal from the top to the bottom slot, sobear this in mind when setting up more complex routing. Just drag and drop the desired effectsto Insert slots on the input channel you're using — remember that you can re-order them bydragging them around as well. For example, if an input channel has (from top to bottom) peakmeter, send, and EQ Inserts, you'll get a clean signal sent to your audio application, but hearthe EQ'd version when monitoring through the DSP mixer. Conversely, a guitar sent throughan input channel with peak meter, distortion, and send Inserts will record the distorted signalas well as monitoring it.

Patchmix DSP Tips

If you think your playback signals are quieter than normal, you've probably loaded aSession containing -10dBV instead of +4dBu output levels — you can change them byclicking the Session Settings button and selecting the I/O page, where you'll find all thecurrent settings of both inputs and outputs, including the configuration of the PCI card'soptical input and output (ADAT or S/PDIF).

Don't worry if you can see signal activity on a peak meter inserted in the 1820/M Dock In3L/3R inputs when you have nothing plugged into these jack inputs (or hear lots of hisscoming from this stereo channel through the monitor mixer). This is because the high-gainRIAA-equalised turntable (phono) preamp shares these input channels, and remainsactive until you plug something into the Line 3 L/R jack sockets. To remove this hiss fromthe monitor mixer output, just click on the channel's Mute button. Similarly, to minimiseany contribution from the mic preamps when you're not using them, click on their channelMute buttons. This will ensure that background noise levels remain as low as possible onthe main mix output.

If you create a useful mixer setup, don't forget to save it for posterity with a descriptivename so you can use it again later on. This will save both time and frustration.

The Insert Test-tone/Signal Generator includes a sine-wave oscillator that I've found reallyhandy for tuning instruments. Just temporarily insert the oscillator on any mixer channelnot playing back the instrument in question and type in the desired frequency — such as440Hz for a concert 'A'. Then you can tune the instrument to the test tone.

Emu's WDM drivers currently only support a single stereo input and output, which somemusicians find incredibly restricting. However, the vast majority of professional audioapplications now support ASIO-format drivers, and these do support full multitrackoperation. Only those few multitrack applications that don't offer ASIO driver support (suchas Adobe's Audition, previously called Cool Edit Pro) will therefore be restricted tostereo-only operation, but hopefully this will change in the future.

More Complex Signal Paths

If you want to record the mixed-down stereo output from your MIDI+Audio sequencer, plus thecombined stereo mix from a set of hardware MIDI synths being triggered from MIDI tracks, it'seasy using the Patchmix DSP functions. Just create your combined mix using the various inputstrips, and then add an Insert Send (Output To ASIO/WAVE Or Physical Out) to one of theMain Inserts to return this combined mix to a stereo input pair on your sequencer.

You can even send signals from one application to another through the mixer. For instance, ifyou choose the stereo MME-WDM E-DSP Wave output option in an application like Wavelab,its signal will appear in the Patchmix DSP mixer on the Wave L/R stereo playback input strip.Then, if you add an Insert Send (Output To ASIO/WAVE Or Physical Out) to one of the HostASIO In options, this stereo signal can be recorded directly into Cubase/Nuendo or any otherASIO-compatible application.

You may instead want to patch external hardware effects into some sequencer tracks, andagain Emu have made this comparatively easy — you just route the stereo signal in questionto an ASIO output in your multitrack sequencer application, make sure this ASIO outputappears as a channel strip in the Patchmix DSP mixer, and then choose the InsertSend/Return (Physical Output And Input) option in one of its Insert slots. Choose the physicaloutput and input sockets to which you want to attach your external effects (including S/PDIF ifyour hardware effects box has digital I/O and you need a cleaner signal path that doesn't passthrough A-D and D-A converters).

Another example of a complex setup that's easy to create is where a guitarist wants to recorda guitar with Pod-style modelling effects, but also record it dry (in other words with no addedeffects) in case the sound needs to change later on. To do this on the 1820M, just plug yourguitar into the Line A or B inputs, add an Insert Send (Output To ASIO/WAVE Or Physical Out)near the top of the Insert chain to any available 'Host ASIO In' to send this dry signal to your


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sequencer, then add an Insert Send/Return (Physical Output And Input) below it, and patchthe Pod input and outputs into the chosen send and return sockets on the Audiodock I/O box.You'll be able to hear the treated (wet) signal through the Main or Monitor outputs of the EmuPatchmix DSP, but both wet and dry signals can now be simultaneously recorded in yoursequencer onto separate stereo tracks.

Once you've got your head round the routing options I've discussed here, you should be ableto work out plenty more to suit your individual requirements — just remember to have a peakmeter inserted into each mixer channel, and then you shouldn't lose your signals ever again.

Published in SOS November 2005

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emu's patchmix dsp demystified

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