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What's up with noise reduction in the Megahertz range and why does it matter?

4/1/2019

12 Comments

 
Picture
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:
Picture
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.

PictureNodes On A Vibrating String

​Thepoint 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 Bosendorfer 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 by product 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.
12 Comments
paul davies
4/6/2019 08:44:13 pm

megahertz hetrodyning your talking about digital problems again the pure analogue domain only has 20-20 hhz with these effects to worry about is enough

Reply
Aldo Cugnini link
4/11/2019 07:36:46 pm

The explanation given is incorrect. The beat between two frequencies is a perceptual phenomenon: it does not actually exist, it is only perceived in the brain. Hence, in order to "hear" the beat, the two individual tones must also be heard, and the human auditory system simply cannot hear anything above 22 kHz at most. Thus, it is irrelevant as to whether the medium is analog, digital, vinyl, magnetic tape, or whatever. -agc

Reply
Dennis Han
4/15/2019 01:20:15 pm

This is not digital problem, it is an analog problem for DSD since some DSD DACs don't have a low-pass filter at the output and the noise floor rises about 20 kHz. Filters also need to be used with a DSD ADC to avoid encoding noise as described next.

The description of hetrodyning is correct. Nothing is perfectly linear, even amplifiers with 0.001% distortion, and especially not speakers. Any two signals will produce a sum and a difference signal. If the two signals are 5.00 MHz and 5.01 MHz, then the difference signal is at 10 kHz. If filtering is used above 20 kHz, I use 30 to 50 kHz, then the amplitude of the noise (I'm calling noise anything that is not part of the intended audio signal) is reduced a lot and the hetrodyning effects are also reduced a lot.

Reply
Hair Bow link
4/27/2022 04:43:21 am

Wow! I didn't know before what's the importance of reducing noise in the sound waves, it does really gives out a big impact to our auditory system. This could help to a new wholesome idea in the future.

Reply
building and repair link
4/28/2022 03:26:52 am

This is now actually being studied all throughout the world, looking to treat diseases using sound for example. It really is a good findings and could also contribute to building and repairing components indeed.

Reply
MK Minerals link
7/12/2022 04:34:53 am

Noise reduction is definitely something important.

Reply
Oscar link
7/12/2022 04:36:23 am

It matters alot. If you want something to help you reduce the noise then this is a good feature.

Reply
Paul Davies
7/12/2022 06:17:52 am

If 2 transmitter had antennas and one was 50,000 mhz carrier and the other 50,001 mhz would we here a 1khz beat?Also apart from electronic musical instruments dont produce a perfect single sine waves

Reply
Dennis Han
1/20/2023 09:39:32 am

The receiver that receives those two signals would produce, due to its non lineariities, a sum and difference of those frequencies -- 1 kHz and 10.001 MHz (I'm assuming you meant 50 and 50.001 MHz and not 50 GHz), and then sums and differences of those frequencies, etc.. That's called intermodulation distortion. It exists in all electronic amplifiers with the very good amplifiers reducing the distortion to a very low level.

Reply
John link
10/13/2022 02:34:35 pm

The study also shows that sounds in the higher-frequency range of around 2,000 to 5,000 Hz were rated as most unpleasant.

Reply
https://www.lenexalandscapelighting.com/leawood-landscape-lighting.html link
12/1/2022 05:23:41 am

What techniques can be applied to reduce noise and interference in measurement systems?

Reply
http://saratogamovingcompany.com link
1/20/2023 05:01:16 am

Low-frequency sound are often “lower' to the human ear while high-frequency sounds can start at above 2000 Hz.

Reply



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  • Home
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    • PranaWire >
      • Sukhavati
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      • Power Supply Related Products >
        • USB Isolator
        • CB-1DB Receptacle Wall Plate
      • LAN Isolator
      • PC & Newtwork Audio Related Products
      • RR-888 Ultra Low Frequency Generator
      • RGC-24 Ground Conditioner
      • REM-8
    • Oyaide
    • Acrolink
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