Glen O'Hara, staff 5.1 engineer at Porcupine Studios in Chandler, Ariz. also teaches digital audio and post production audio at the Conservatory of Recording Arts in Tempe, Ariz. and is a contributor to Pro Audio Review.
The design intent of the MTI-3 is to radically widen the stereophonic sweet spot by adding a center channel to the left and right and then inserting electrically matrixed signals into all three channels.
Product Points
Applications: Installed systems; church auditoriums; multimedia; studios; home theater; DJ
Key Features: Source gain control; source balance control; TriSonic setup switch; SpreadSound switch; TriSonic balance; surround control
Price: MTI-3 - $599; MTI-3A - $649
Contact: Miles Technology, Inc. at 800-280-8572.
Plus
+ Easy to set up and use
+ No coloration, pumping, out-of-phase, flanging, or other undesirable effects
Minus
- None
The Score: Does just what it was designed to do: widens the stereophonic sweetspot.
Unlike the Pro Logic systems, which steer phantom center audio into the center channel, the MTI-3 inserts matrixed information into all three front channels to obtain the design intent of good left/right and center perception (over a wide listener location), without the steering effect many listeners find objectionable.
Features
The MTI-3 has two derived surround outputs with separate gain control. The left-right difference signal contains ambient and reverb information on stereo recordings and intentional surround effects on Dolby encoded movies. The TriSonic Imager's dispersion matrix increases the relative level of these sounds in the left and right loudspeakers while maintaining complete cancellation of them in the center channel.
When the surround outputs are used to feed rear loudspeakers, a very even, four-speaker surround effect is created. This is accomplished in Miles' SpreadSound circuit by providing the two surround outputs in quadrature phase (90 degree phase difference) at all frequencies from 100 Hz to 10 kHz, greatly reducing surround localization, to prevent in-the-middle-of-your-head and out-of-phase effects.
The single rack-space MTI-3 is professional throughout. Balanced XLR jacks and 1/4" TRS are provided for inputs and left-center-right outputs, with XLR only for center input, surround input and surround outputs.
Manufacturer's specifications are frequency response of 20 Hz to 20 kHz +/-1 dB, with total harmonic distortion less than 0.02% across the same bandwidth from inputs to any output.
On the front panel: source gain control; source balance control; a TriSonic setup switch (allows amplifier gain adjustments for left to center and right to center midpoint imaging - switch must be out for normal operation); SpreadSound switch (spreads the sound smoothly across the entire soundstage when pressed - particularly useful for mono source); TriSonic Balance; and Surround Control (level control for surround outputs, LS, RS).
On the rear panel: right channel polarity switch (designed for the optional bridged-center loudspeaker connection) and surround filter switch (changes frequency response of surround outputs from 20 Hz to 20 kHz down to 100 Hz to 7 kHz).
A 26-page instruction and application manual is included. The manual is clearly written and contains many applications and connection diagrams.
In use
The MTI-3 was a pleasure to set up and use. Its straightforward design added no coloration, pumping, steering, out-of-phase, flanging or other undesirable effects. Its design for professional applications was evidenced by its XLR and 1/4" TRS balanced connections throughout.
I was immediately able to effect the stereo spread by using the TriSonic balance control. In the normal position, I listened to a variety of music and movie mixes, plus experimented with on-the-fly mixes with hard left, hard right and center pan positions.
Having a gain control for the surrounds became very useful as I noticed the differential content varied quite a bit over the wide range of music and soundtracks auditioned. I also found moving the TriSonic balance control slightly toward the center indication was more pleasing for movie listening and music with a lot of ambient sound and reverb. Moving the TriSonic control past the normal indication through sides to its most clockwise position (labeled "diff") gives the listener an idea of what the circuit is doing by exaggerating side insertion of the matrix signal. Dialogue and any mono information in the stereo mix is totally summed out in the diff position. During all my subjective listening tests, I found somewhere between the center and normal position the most pleasing.
Using the MTI-3, even from extreme left and extreme right listening positions, a good stereo mix was perceived. I experimented with sitting far left (and far right), then doing some left to center to right panning. The perceived image would pan smoothly, at a consistent level.
When sitting far left, a hard right pan is perceived to come from the right, but not the right speaker. I have quite a bit of material recorded with stereo pairs of microphones over a guitar, piano, etc. and noted a full spatial image from all listening positions.
Summary
The MTI-3 does just what its designer intended - it widens the stereophonic sweetspot. As a piece of hardware, this unit is simple, straightforward and well-manufactured. Vintage analog hounds out there will enjoy the one knob approach. Just using the left-center-right outputs, live sound applications will present a stereo image to all seats in the venue - even with hard pans in the mix.
The MTI-3 ($599) uses an outboard power supply (brick in the cable). The MTI-3A ($649) more conveniently incorporates the power supply internally without increase in chassis size.
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