May 2019

What's Up With Noise Reduction In The Megahertz Range?
And why does it matter?
Article By Joe Cohen Of The Lotus Group

  There is a very simple explanation for why this topic is so important. It comes via my technician when I asked him why he thought the PranaWire Linebacker was so effective. Earlier I wrote that when he measured its effectiveness he was expecting to find no greater than 10dB or perhaps, at the extreme, 15dB of reduction. What we found instead was that the attenuation we were able to measure was at the noise floor of the measuring equipment. In other words we were only able to measure to 60dB of attenuation before the noise generated by the equipment itself masked further results. Though measuring equipment with higher resolution exists, and I would be very happy to see those results, I am content with being able to say that the attenuation is at minimum 60dB.

If you are familiar with how a piano is tuned you will understand immediately, but for those who do not, let me digress into what is happening with "just" verses "tempered" intonation which will have bearing on my explanation:

The intervals in just intonation are derived from the physics of a string. When you allow your finger to lightly touch a string at exact fractional distances between the bridge and the nut you will hear different tones. The table below explains:

So we can see from this chart that the octave, fifth, third, minor third, natural second, minor seventh and major seventh are all derived from the natural harmonics of the string.

The point is that there is a physical basis for the derivation of each note based on the actual subdivisions of a vibrating string. This is what happens naturally on any single string of an instrument whether on a Bösendorfer or a one string Indian Ektar. When viewing a video of a vibrating string in slow motion, you can actually see these nodes at work.

The tempered scale was invented for the purpose of creating the ability to transpose from any of the twelve keys into any of the others while maintaining exact proportional relationships. In order to accomplish this the naturally derived scales had to be slightly and precisely detuned.

When two strings on an instrument that are out of range of each other are gradually brought closer together in intonation there is a threshold of closeness where they will begin to interact by creating a rapid beat. As they are brought closer and closer to the center of the pitch the beat slows until, at zero, the beating disappears altogether. When tuning the intervals on a piano, the technician listens for and counts the beats per minute (generated by detuning) to determine the precise intervals that create a proper tempered scale.

So what happens when two frequencies in the megahertz range are within beating distance? They behave in exactly the same manner as two strings. The periodicity of the beating generates a fundamental that occurs within hearing range. Noise is a cloud of frequencies. As a result there are myriad frequencies interacting, generating a myriad of audible fundamentals. High frequency generated noise can and does impinge on the circuitry within a given component affecting the manner in which signal is delivered to the next component and so on. It impinges from without (other components, cables, home wiring, phones, Wi-Fi etc.) and also as self-generated noise from within. The attempt to generate signal has as a byproduct this "dark matter" called noise. A system comes into being in an environment already rife with noise, and the complexity of interactions within it and its environment are likely beyond our current means of measuring except in the broadest sense.

When we remove high frequency noise from a system, audible veils are removed. Therefore, the absorption and dissipation of high frequency noise is a topic that should be of paramount concern to all who design components and those who seek to put them together into a coherent whole.

The Lotus Group 
Voice: (415)897-8884
E-mail: joe@lotusgroupusa.com
Website: www.LotusGroupUSA.com