Dirac Live Room Correction Suite
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Digital room correction. Or should we call it virtual room correction since we're not correcting the room, we're adapting the music's bits during playback to better suit the room. But in order to correct something, you first have to understand what, if anything, needs correcting. Of course you can perform room correction by ear and you very well may come away with a sound that suits your tastes. But to really understand what's going on with the sound in your room, you need to analyze. You need to abstract the musical information into forms that represent various aspects of sound. The Dirac Live Room Correction Suite not only shows you how your music looks, it also shows you how they feel it should look.
The Dirac Live Room Correction Suite, which is intended specifically for computer-based audio, consists of two applications—The Dirac Live Calibration Tool which requires a microphone, and the Dirac Audio Processor that implements the filters you create using the Calibration Tool. I used the Dirac-recommended XTZ Microphone ($140) which makes things easier as its calibration file is provided with the Dirac software. Using the Dirac Suite was simple and very straight forward and so was hearing its effects through the custom-for-my-room filters. The real question is—do you like being corrected?
What the Dirac Calibration Tool does is measure your room's frequency and impulse response and then automatically generates an optimization filter to turn your lumps and bumps into a smooth line. Jack LaLanne for your hi-fi. To dig a little deeper, the Dirac software uses a Mixed-Phase filter, "that matches a desired magnitude response [more commonly called Frequency Response] while also having a customized impulse response". According to Dirac, a mixed-phase filter is more difficult to design as compared to the more common minimum-phase and linear-phase filters, "...neither of these two filter designs can make a desired change to the phase or impulse response, unless the desired change is exactly the particular change they make by definition". So to put another way, the Dirac software looks at (or listens to) and presumably corrects your hi-fi's in-room frequency response and optimizes your time domain response.
I'll just point you to the Dirac website's technical description page for more information since I would just be repeating what they have to say. Instead, let's focus on using the Dirac Live Room Correction Suite.
Using the Calibration Tool is a snap. After loading the associated software, I connected the XTZ USB Microphone to its included USB microphone amplifier and then to my MacBook Pro and launched the Calibration Tool software.
The first screen asks you to select your system configuration. The Dirac software works with up to 8 channels but I use just 2 so I selected "Stereo Speaker System". The Test signal playback device is your DAC so I selected "Mytek_Firewire" and the filter can work with sample rates up to 96kHz. Music files with a sample rate higher than 96kHz will get downsampled when played back using the Dirac software.
Next you select your Recording Device, which was the XTZ Microphone in my case which showed up as "USB Advanced Audio Device", and load its associated calibration file (optional). Since the Dirac Suite comes with the calibration file for the XTZ mic all I had to do was select it.
Then you set your output levels. If you think you could use more details for any of these steps, there's an on-screen Help section for each page that gives you all of the information you need. I did not include this in my screen shots because it made the image too small to read but trust me, its there. There's also a 40-page PDF manual that I only had to reference once or twice.
Now's the fun part. First select the type of listening area you have, I selected "Chair", then position the microphone where the picture tells you to and click "Start". There are three views to look at in order to help you place the mic in three dimensions. Once you place the microphone where you're supposed to and click "Start" the Dirac software plays three sweep tones. All in all you go through 9 positions around your listening area (my chair in my case). When you're finished, you get to see what kind of shape you're in.
Showing your in-room frequency response is like taking a shower in a public bath—your shape is there for all to see. Now I know that I have not been exercising much lately and I've let my eating habits be ruled less by health and more by taste as is clear from that graph. Oh wait a minute, I meant to say that even though I treated my room with some homemade room treatments and spent some real time arranging my hi-fi and speaker setup, I did so according to taste. I had more room treatments in place, and less, and settled on the current setup when things sounded really good. Compared to an untreated room, my current setup sounds very rich and there's very little sense of the room. What I mean by that is the music is not contained by the walls nor does it obviously project from the speakers. It just is, so to speak.
But as you can see from that graph, my room is lively and that orange line is the recommended/optimized target for the correction filter. You can click and drag those circles/break points to tailor the response to your liking and by double-clicking on the orange line you can add more break points. I went with Dirac's recommendation by clicking "Optimize" and then "Save Filter". You also need to save the Project by clicking "Save...". This way you can Load your saved Project and use it to make new filters if the feeling moves ya. And I'm betting it most certainly will.
Next you open the Dirac Audio Processor and your Media Player of choice. You have to set your computer's sound output and Media Player to point to the Dirac software. The Dirac software points to your DAC. "Click to Load" in the Dirac window brings up the filter(s) you just made in a browser window and all you have to do is select your filter and turn it "On". You can load multiple filters simultaneously but only one, the one that's highlighted, is active at a time. There are also Gain & Delay data associated with each filter that the Dirac software automatically sets as part of the calibration process. You can edit these settings in the Processor software for both channels simultaneously or individually. I left these in the default settings.
I mainly used Pure Music with the Dirac software but also tried Audirvana Plus for these listening sessions. While the Dirac software worked fine with Pure Music, it only worked sporadically with Audirvana when iTunes Integration mode was engaged. It worked just fine with Audirvana in playlist mode.