The Absolute Sound - Bruce Brisson Interview by Robert Harley



MIT Founder Bruce Brisson Talks
with Robert Harley

Tell me about your background and how you began designing cables.

My wife Kathy and I always enjoyed music. In 1976 we bought a Pioneer rack system, but quickly moved on to a full Marantz system with the Model 7 preamp, 8b power amplifier, and 10b tuner. I began experimenting with bi-amping and then tri-amping, but since I added the amplifiers over time I ended up using different speaker cables for each connection. The cables were from Monster Cable, Mogami, and Fulton.

One day the crossover broke so I took apart the system to fix it and when I put it back together it sounded different. I had not paid attention to which cables were connected to which drivers, so I ended up with different cables on different drivers than in the original configuration. When I turned on the system it didn’t sound the same. I took every-thing apart and retested it, but was puzzled because everything worked correctly. And then I asked myself if mixing up the cable brands connecting the different drivers could be the cause. I put it back together the way it initially was, and the sound returned. That got me interested in how cables can affect the sound.

A few years later I was working at Fairchild Semi-conductor where I met a guy who repaired test instruments for Hewlett-Packard. He enjoyed music and would bring his records over to my house. Being an employee of HP, he was able to borrow any piece of test equipment it made, and would bring the instruments over while we listened. Between the test instruments and the listening, I was starting to understand the phenomenon that made cables sound different. I began to think of a cable design that would be better than anything previously built.

Around 1980 I was in a group of San Francisco audiophiles called the Hands On Audio Society. Some of the guys listened to my home-made cables and many wanted to buy them. An employee of Monster Cable heard about my cables and said that [Monster Cable founder] Noel Lee wanted to meet me. I showed him an interconnect design and he listened to it, and asked me to make a sonic change, which I did. I modeled the cable mathematically on a Tandy Model III computer running VisiCalc, and then patented the design. I licensed the design to Monster and it became their Interlink Reference. Many consider this the first true audiophile interconnect. I developed about eight other cable products for Monster, and then founded Music Interface Technologies in 1984.

MIT was the first company to use networks in cables. Why do cables need networks?

As with any passive network, cables contain both resistive and reactive components. This creates resonances and anti-resonances in the cable. A series resonance is when the reactive components cancel each other. At the resonant frequency the complex impedance will be quite low. This series resonance doesn’t impede the signal flow in a cable. An anti-resonance, however, is formed when the reactive components add together to form a highly complex impedance. This “parallel resonance” does impede signal flow in the cable.

It’s generally assumed that the electrical bandwidth of an audio system should be ten times greater than the audio bandwidth. That is, the electronic components should operate out to at least 200kHz. So, what are the first issues that cause distortion when a cable doesn’t work well within that band of frequencies? Cables suffer from a parasitic series resonance at frequencies below about 1.5kHz and from parallel resonances at higher frequencies, determined by the values of the inductance and capacitance. The cable doesn’t function as an ideal inductor. All audio products act as low-pass filters. Cables without networked terminations function as a lossy low-pass filter because of this parasitic capacitance as well as shunt capacitance. The vector seen at the input terminals of an audio signal-carrying cable should be an inductive vector at all frequencies and at all power levels.

We can correct for the parasitic and shunt capacitance by adding reactive components in the network that will offset these effects.

A conventional [non-networked] cable will also operate in a “bi-stable” state. State analysis shows that a system can work in three states—stable, astable, and bi-stable. A cable carrying a low signal level will function in a bi-stable state because of the parasitic capacitance within and between the individual conductors, which when twisted or coiled together form the inductor of the cable. The low-level signal must overcome this parasitic capacitance before it can pass current (the audio signal). So the cable shifts between a capacitive element and an inductive element many times per second because of the audio signal’s varying amplitude. The cable must carry sufficient current to overcome the parasitic capacitance. That makes the cable bi-stable.

During the time it takes for the cable to shift from being astable to stable, the low-level signal carried by the cable is turned into noise. We call this “analog jitter.” Removing analog jitter is one of the reasons why MIT cables have such a black background and have such good low-level detail. The result is proper timbre, transparency, soundstage size, and point-point location of images. No jitter equals no noise component.

Think of a cable carrying two tones of the same frequency, but one is very high in level and the other very low in level. With MIT cable the low-level signals remain intact and are not converted into noise, and are sent in-phase with the high-level signal. Also, the harmonics of the low-level tone are transported in time within the complex tone’s envelope.

All of this describes the technologies I’ve developed over the years: “2C3D,” “JFA” and “JFA-2” (“Jiiter-Free Analog”), and “SIT” (“Stable Image Technology”). SIT means that the image of the instrument or voice won’t move within the soundstage.

The circuit elements in our networks are “time invariant.” That means the relationship between the input and output signals doesn’t change over time. The system should not respond differently to the same input signal at different times.

We have a whole range of impedance analyzers that we’ve bought over the years. We can increase or decrease the applied voltage and measure the impedance with varying power levels at any frequency. This allows us to fully characterize any capacitive or inductive component we use in any given cable. MIT is the only cable manufacturer that quantifies the performance of the products.

Can you explain the concept of “poles of articulation”?

A pole of articulation can be thought of as a pole that is holding up a tent in the center.

The tent will have a slope or skirt associated with it on both sides of the pole. Electrically, a pole has a magnitude and it stores energy. How much energy the pole stores is determined by the size of the storage elements—linear capacitors and inductors. Capacitors store voltage for a period of time and return that voltage back to the cable or network. Inductors store current for a period of time and return that current back to the cable or network. If the capacitor or inductor is larger it will store more energy. An articulation pole stores energy and then over a predetermined amount of time can deliver energy to the load.

All cables have one articulation pole, the point where it is most efficient at transporting energy, which is usually around 1500Hz. This is why most cables sound OK at about 1.5kHz but sound brighter at high frequencies and muddy at low frequencies. With just a single articulation pole the first few harmonics of middle C and A are not correct with regard to timbre, and won’t image properly. We end up with an articulation response in conventional cables that is shaped almost like a bell. The highest point in the bell-shaped curve is the highest articulation frequency of the cable, again, about 1.5kHz. We add more poles of articulation above and below that frequency by adding additional capacitive and inductive elements to produce a straight-line articulation response. The first technology we invented that helped overcome these issues was our MIT 2C3D Technology. I wrote a paper about this in 1991 called “Transportable Power in Audio Cables and Energy Storage Elements.”

Going back to our Jitter Free Analog technology, the new version of that, JFA-2, is the primary reason the Articulation Control Consoles are so sonically superior to the Oracle products before them. The Articulation Control Consoles also use a very improved 2C3D technology, which also helps imaging and soundstaging with-in the very important frequency range of 80–800Hz.

Why have you included impedance adjustments on the interconnects?

Because all audio components have different impedances, the network’s articulation response will vary with that impedance. The adjustable impedance allows the user to optimize the articulation response for their particular components.

The MIT white paper titled “The Effects of Audio Cable as Related to Articulation of Speech and Music” includes the articulation responses, in percentage, of cables I had measured into different impedances. I helped design the FFT analyzer along with a Hewlett-Packard engineer. It uses a “single-shot unit step pulse” not a swept sinewave. This is a dynamic measurement. The measurement uses as a reference the “unit step pulse” spectra in both magnitude and frequency against a clock in the computer. This is a one-of-a-kind FFT that cost me about $135,000 to build back in 1998.

Using this analyzer, we show in the white paper the articulation plots of various cables. You can see immediately what happens when the cable is not terminated into the proper load impedance. The articulation response suffers. We developed a technology called “Impedance Specific Networks” that allows the user to switch between three impedance settings and optimize the interface for his components.