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Product Review
 

Lexicon MC-12 7.1 Surround Sound Processor:  Automatic-Room Correction

January, 2004

John E. Johnson, Jr.

 

Click the photo above to see a larger version.

Specifications

● Codecs: Dolby Digital, Dolby EX, Dolby Pro Logic II, DTS, DTS ES, DTS ES Discrete, DTS Neo:6, DTS 24/96, HDCD
● Digital Audio Inputs: 6 S/PDIF RCA, 6 S/PDIF Toslink, 1 XLR
● Audio Outputs: 12 RCA, 12 XLR, Including 2 for Future Use
● 4 Analog Devices SHARC 32-bit DSP Engines
● THX Ultra Certified
● Cirrus Logic's Crystal CS49326 DSP decoder
● Input Impedance: 100 kOhms
● MFR: 10 Hz - 40 kHz - 0.75 dB
● THD: 0.003%
● 24/96 A/D, 24/192 D/A Differential Balanced in All Main Channels
● Zone 2 Operation
● Video Switching: Component Video at 300 MHz
● Size: 6.6" H x 17.3" W x 14.8" D
● Weight: 45 Pounds
● MSRP: $10,000 USA; Calibrated Microphone Package Option $795 USA

Lexicon, Inc.

www.lexicon.com

Introduction

At CES, 2004, one of the hottest new things for surround sound processors (SSP) and receivers was Automatic Room Correction (ARC). Several companies were showing products with this feature, and so we decided it was time to review one to see how the latest technology performs.

In 2003, we reviewed the Lexicon MC-12 Surround Sound Processor, but at that time, we did not have the latest option package for ARC. In order to use the ARC feature, you need to purchase the set of 4 calibrated microphones that are designed for its use (a $795 option). We obtained another MC-12 and microphone package for review.

There are other processors and receivers that have now or have had various aspects of room correction built-in. However, it takes a massive amount of DSP to perform the calculations, and the MC-12, with its 4 SHARC processors, is at the leading edge in terms of modern sophistication. It uses 4 microphones (most ARC systems use 1 microphone) that can be placed to give you the best compromise for multiple seating position situations. That takes a lot of processing power that has only become available recently.

Since the basic MC-12 features have been covered in our previous review, we will concentrate on the the auto room correction for the present review.

If one were to automatically correct a room using software and processing power in an SSP or receiver, it would include several things: (1) correction for distances between the various speakers and the listener; (2) correction for volume in each channel; and (3) EQ for each channel. The current Lexicon automatic room correction system handles (1) and (2) above, but not (3), although EQ correction for the lower octaves will be in the next software version coming in a few months. Correction for the high frequencies is unlikely since the wavelengths are so short, all you have to do is move your head an inch forward, backward, or to the sides, and the EQ changes. Therefore, EQ in future SSPs will most likely just be for the lowest octaves. Lastly, early reflections and standing waves are only correctable with room acoustical treatments (placing absorption panels on the walls), rather than something that is adjustable in an SSP.

So, let's call the current MC-12 software ARC Minus 1 until the new EQ software arrives. In any case, automatic distance and level correction are important enough that we will talk about those two features now, and update you with the EQ feature when it arrives in our editorial offices. Some might argue that automatic distance and level calculation is not anything you can't do with a tape measure and Radio Shack SPL meter. That's true, but if the SSP or receiver will do the work for you, it means that much more time you can spend watching movies and listening to music. Secondly, the Radio Shack SPL meter is not calibrated, and can be off by a few dB at various frequencies. It is fine for comparing relative speaker levels between channels but cannot be considered accurate to within 1 dB in its readout at all frequencies. Also, the processing power of the MC-12 lets you calculate the best compromise for several simultaneous listening positions, and that is something you really can't do manually.

The Procedure

The MC-12 has 4 SHARC processors, and they are all used in calculating the room correction.

A set of 4 microphones is packaged in a separate hard carrying case, and consists of small AKG C-98 microphones with very long cables. Each microphone is placed in a microphone clamp that is screwed to individual table-top stands.

The microphones are placed at the main listening position, with each microphone as close to the others as possible. A photo below shows the setup that we used for the review.

The other end of the cables is a 0.25" mini-plug that is inserted into one of four microphone jacks on the rear panel of the MC-12. The jacks are in the center of the photo shown below, and you can click on the picture to see a larger version.

Now you turn on your audio system and are ready to go. You need the remote control for doing all of this (photo below, right), and also the On-Screen Display (OSD) should be viewable on your TV (you can perform the procedure using only the front panel display, but it is much easier with the OSD on a TV screen). I send component video from my DVD player directly to the projector rather than going through an SSP, but the OSD is displayed with S-Video out, so I connected the S-Video from the Lexicon to my projector and just switched from component video when I watched DVDs, to S-Video to use the OSD for changing any particular parameter.

The first menu is shown below, left, which is accessed by pressing "Menu" on the remote control.

Click on the photo above to see a larger version.

Selecting Setup brings the menu shown below.

For our tests here, we select Speakers, bringing the menu below. Before ARC is performed, you need to set any crossover points that you want, as selected in the menu below.

After that is done, you select Check Microphones, and the menu shown below comes on the screen.

Pressing the right arrow key then brings a screen that says "Testing for Silence", followed by the menu shown below.

The results of the microphone check are shown below. Each microphone has been tested and is "OK". If one has a problem, it will be labeled with an error. It would not be used in the calculations.

Once the microphones have been checked, you go back to the Speaker Setup menu and select Automatic, which gives you the menu shown below. For our tests, we selected Distances & Levels, since we wanted the Lexicon to set both of those parameters. The menu reminds you to put the four microphones in the primary listening position.

Continuing on, the next screen is shown. It tells you that you have 10 seconds to leave the room or remain quiet. I sat there and plugged my ears, as the test signals are loud and high frequency. They appear to be sine wave sweeps rather than pink noise.

Once 10 seconds have passed, the testing begins, and you see the Distances screen, which shows the results for each channel as each channel is tested individually, including the sides for a total of 7.1. In our case, the center channel test had a problem, which was caused by the fact we use two speakers instead of one. The system is obviously very picky about determining the answers. We ultimately got a center channel distance of 7 feet by disconnecting one of the center channel speakers and redoing the auto distances calculation.

The subwoofer output had been set to mono, but if you have stereo subs, the calculations will include both subwoofer outputs as long as you set the subwoofer menu to include stereo subs. There is an LFE subwoofer output that can be tested too, and there is a separate LFE output jack that has to be turned on in this case.

For Levels, here are the results.

Once the tests are completed, you can backtrack through the menus and see what the settings are in the Speaker Setup Manual menu, which now contains the settings determined by the Automatic procedure. The first one is the Distances. It has the settings from the automatic testing, which I confirmed.

Then you can check the Levels to see that the auto results are there, which they are.

That is it. You are done with Automatic Room Correction for Distances and Levels using the seating position where the microphones were located during the procedure. The whole process worked without a hitch in our tests, and we were delighted with the results. One interesting bit of serendipity is that the testing revealed that one of our speakers was wired out of phase. This was indicated in the tests as an Error next to that channel. Using the down arrow, a sub-screen popped up saying that the speaker was out of phase. Reversing the speaker cables fixed the problem. I imagine this problem was detected through the MC-12 looking at the impulse response that it got when the test signals were received from the speakers and processed. The initial wave should be positive. If it is negative, then the speaker is out of phase. The problem is that some components invert the signal, and since we often have several components in the signal chain, including two different power amplifiers in our case, it is difficult to know if everything arrives at all of the speakers in phase. The MC-12 lets you know if there is a problem. This is really something you can't do manually with just a tape measure and an SPL meter.

The sound quality of the MC-12 is one of the smoothest of any SSP I have ever heard, and with the utilization of ARC Minus 1, the sound stage is much more cohesive and focused. Besides the forthcoming room EQ addition which will make it full ARC, I would suggest that Lexicon add a few memory banks to store at least three user setups. This would allow us to have one ARC memory setting for one particular sitting position (say 1 person watching a movie or listening to music from the sweet spot), a second ARC memory setting for another situation (the whole family sitting in several positions, watching a movie), and a third ARC memory setting for impressing your friends (with the subwoofer cranked up).

Conclusions

The Lexicon MC-12, with its balanced DAC configuration and myriad features which now includes automatic room correction, sets new standards of performance in an SSP. We awarded the MC-12 our Secrets Best of 2003 for SSP Technology, and it is well deserved recognition for a very fine component.
 

- John E. Johnson, Jr. -

Copyright 2004 Secrets of Home Theater & High Fidelity

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