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Cable Asylum Interconnects, speaker wire, power cords. Ask the Cable Guys. |
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Cable Asylum Interconnects, speaker wire, power cords. Ask the Cable Guys. |
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In Reply to: MIT Cable--- How They Work, What they Do posted by NegWAF on March 13, 2007 at 06:38:16:
their intent is good but their approach is inherently flawed.The big remaining mystery to most folks interested in high-resolution audio is the topic of out-of-band noise. Most folks agree that human hearing frequency response is limited to about 20KHz at the upper end. Some might argue that information up to about 50 KHz still affects perception of stereo reproduction. However, audio electronic equipment can generate and/or respond to electrical noise up to the UHF band and beyond: say 100 MHz.
The spectral range from 50 KHz to 100 MHz contains no useful audio-band information. Unfortunately, noise in this range can interact with the audio-band signal anywhere there is non-linear conduction, such as inside transistors or at dirty contacts. This interaction is similar in principle to what happens inside a radio receiver: the intermodulation products include audio-band products. In the case of out-of-band noise, these products are spurious tones that mimic overtones in the recorded signal.
Symptoms of this kind of noise include excessive brightness, enhanced 'detail' and sibilance, mushy cymbals, a harsh and mechanical midrange, a vague sound-stage for acoustic bass instruments, an artificial "black" background that swallows up natural decay, a forward and compressed sound-stage, sound-stage instability with changes in pitch or loudness, blurry massed strings or choral voices, and a general sense of nervousness in most music that should be warm and relaxing.
The out-of-band noise can come from equipment power supplies, both linear and switching, digital processing in CD players and the like, local non-audio appliances such as computers, DVRs and microwave ovens with computer control, and wireless communications equipment within and outside the home.
A first-order approach to reducing the effects of this noise are to provide low-pass filters in the cables, to block transmission of the noise from one component to the others. This appears to be the MIT approach.
Whether the low-pass filters in themselves have audible characteristics depends on the skill of the designer. However, I don't like the approach because, no matter how skillful the designer, the cables between the filters and the terminations can still act as RF resonators.
Resonance is a familiar phenomenon. Bridges fall down if their resonances are not damped or controlled. Organ pipes sound loud tones at specific pitches with modest energy input from chaotic air flow at their throats. Electrical cables also have inherent resonances if their terminations are not properly designed. These resonances fall within the out-of-band noise spectrum that can degrade audio signals. Strong tones due to resonances can overcome any filtering or matching measures taken elsewhere in the system.
I've tried to make this explanation as simple as I can. If it is not clear, then imagine how difficult it is for the person writing the advertising copy for audio products. The issue is not secrecy or lack of information, it is the level of education of the target audience.
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- From my perspective, - Al Sekela 09:54:09 03/13/07 (0)
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