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The Truth About Noise (and how to cope with it)

Punter

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The definition of noise is “a sound, especially one that is loud or unpleasant or that causes disturbance”. A technical definition might be “irregular fluctuations that accompany a transmitted electrical signal but are not part of it and tend to obscure it”. Now haven’t these definitions got some awesome trigger words for the Audiophile! Unpleasant… disturbance… irregular fluctuations… and obscure… AAAAAAAAAAAAAAAAAAAAAAAAAAHHHHHHHHHH! Exclaim the golden ear brigade as they run screaming into the night!

However, one man’s meat is another man’s poison and the meat here is for the HiFi product vendors. Noise is their best friend because it’s without doubt second only to distortion as a point of leverage to promote the qualities of their products. How many times have you seen “noise’ trundled out as the primary boogeyman that is being nullified by their miracle products and there’s a bunch of flavours to choose from too. EMI, RFI, hum, buzz, crosstalk, hiss some of these are just different names for the same thing. Conveniently, it leaves so much room for suggestion and disinformation that it’s never run out of steam with respect to convincing the numpty’s that the snake-oil product their looking at will eliminate it or at least minimise it.

What’s your favourite flavour? In HiFi, the favourites are most definitely EMI and RFI as they represent forms of unwanted electrical noise that can, believably, impinge on the quality of the music gushing out of your $200,000 speakers. Now just to be clear, in the normal world, EMI and RFI are different terms for the same thing. This is not the case in the HiFi world because it reduces the number of boogeymen. Vendors always treat them as separate forms of noise subsequently, I will here also. So let’s take a deep dive on those forms of noise.

EMI (Electro Magnetic Interference)

Most of the internet information says that EMI is “unwanted noise or interference in an electrical path or circuit caused by an electromagnetic field (EMF) from an outside source. Also known as radio frequency interference, EMI can adversely impact electronics, causing them to operate poorly, malfunction, or stop working completely.” But this doesn’t fly in the HiFi world because anything connected with “radio frequency” is defined as being “RFI”. So let’s stick with an explanation that leaves out any reference to radio frequencies. Let us not forget however, that radio frequency or RF covers frequencies form 3KHz to 300GHz but more about that later. From all I have read regarding EMI connected with HiFi, it’s generally thought to be in the lower frequency range and that begins with the mains frequency at either 60Hz or 50Hz. Now this is where we will encounter the word “hum” and a sea of frustration. Anyone who has had any experience with audio and amplifiers will be aware of hum. Even if it’s just that momentary surprise you get when you touch the inner conductor of the lead you have plugged into your phono pre-amp and the volume is turned up. In this instance, you’re acting as an inductively coupled antenna and the high gain pre-amp is amplifying the signal that you’re radiating, scary isn’t it, you’re cells are constantly being excited by the mains frequency that’s radiating out of every mains cable around you.

The “Hum Loop”

When hum is referred to generally, it’s in the form of a sustained signal superimposed on the output of the amplifier or other equipment and in this mode, it’s often a “hum loop” causing the problem. A hum loop is caused by the parts of the equipment that are considered at “ground” potential, having no common connection between them. The cause of this can vary. To help explain this, it might be useful to consider an “equipment heavy” environment. A professional recording studio would represent this kind of environment. The primary goal of any recording studio is to get the signal from a source, be it a microphone or a direct injection interface (DI), to a recording device and thus to a finished master recording. There will be many interconnected audio devices in the signal chain and a range of different gain levels in the equipment. Subsequently, any noise introduced into the chain early can affect all of the equipment and ruin the signal. To mitigate this type of problem, all properly engineered studios will have a “studio ground” or “star ground” as part of their construction. This will ensure that the ground connection on every piece of equipment is at the same potential. Hum loops occur when the ground connections on equipment are at different potentials. I have personally experienced situations where there’s around 20V difference in the ground connections between two power points in the same room (not a studio). This is why a lot of live music and stage equipment has a “ground lift” switch, so that a built-in ground loop can be worked around in a venue.
sc900ct.png

The ground lift disconnects the earth connection and lets the signal wires “float” or lifting the ground on one end makes the system “shotgun shielded” (i.e. grounded at one end only). This tactic usually works with a balanced source but it can be touch and go with an unbalanced one. I tend to think that ground loops associated with mains grounds are fairly uncommon with home HiFi setups. In general, the equipment will all be plugged into the same power circuit and therefore, provided the ground connections are solid, there will be no difference in potential on the grounds of the various components.

The only other form of mains frequency hum or noise that could be reasonably expected in any HiFi equipment would be an induced hum caused by electromagnetic coupling. In this scenario, you have a source which is an electromagnetic field generated by the alternating current of the mains power, in the proximity of a high gain circuit. In this case, the hum would be inductively coupled, like in a transformer. If this was happening inside a HiFi component it would indicate that the designer/s of the component were thoroughly incompetent and the unit should be returned to the point of sale and a refund sought. At the user level, if one was to lay the output lead from the turntable to the amplifier along a mains cable in parallel, it is possible that hum could be induced. This would be solved by re-routing the cable. If an alternative route is not possible, having signal cables cross at 90 degrees to a mains cable will minimise the effect.

RFI (Radio Frequency Interference)

Hoo boy! Do the snake-oil vendors love this one! As previously mentioned, radio frequency signals are recognised to be in the range of 3Khz to 300GHz. It seems strange that the lower end of the range is squarely in the region of audible sound but there’s a reason for that.
radio-frequency-spectrum.jpg

Certain types of radio transmission exist at the ELF and VLF ends of the spectrum. These include submarine communications systems. The reason the carrier frequencies of these systems is so low is for the purposes of “penetration” Put simply, the higher the carrier frequency, the higher the free-space attenuation.
RF-attenuation-in-sea-water-41.png

This attenuation is even more pronounced in water and as seen in the graph, ELF and VLF signals have the least attenuation and occupy 3–30 kHz in the RF band, corresponding to wavelengths from 100 to 10 km, respectively. Due to its limited bandwidth, audio transmission is highly impractical in this band, and therefore only low data rate coded signals are used. The VLF band is used for a few radio navigation services, government time radio stations (broadcasting time signals to set radio clocks) and for secure military communication. VLF waves can penetrate at least 40 meters (131 ft) into salt water.

Who knew the RF band included the audible spectrum! Having dealt with that novelty, we can concentrate on the higher frequencies in the KHz, MHz and GHz ranges that we traditionally associate with radio frequencies. RFI is a verdant grassland for the HiFi tweak vendors as the average person has little understanding of it. With the veil of mystery, black magic and voodoo RFI and RF in general can be wheeled out to cause a cold sweat on any High-End HiFi equipment owner. In a practical sense however, it’s a very minor pathway for interference in electronics that are primarily concerned with processing audio signals in the 10Hz to 20KHz band. The reason for this is that HiFi equipment is not designed or constructed to amplify or pass frequencies in the traditional RF bands. Any competently designed equipment will nonetheless have components included to eliminate even the minute amounts of RF that may be induced into HiFi equipment circuits. A case in point is the circuit of the amplifier power supply circuit that I included in my post “The Truth About HiFi Amplifier Power Supplies” thread
35V-PSU.png

In this circuit R2, C7, R4, C15, C8 and C16 are included to ground or filter out any signal component in the high frequency RF spectrum. You will find components in practically all circuits dealing with audio, in an amplifier or disc player or DAC that are included for the purpose of mitigating any unwanted high frequency energy that could compromise the audio signal. This is by design, people involved with the professional engineering and design of audio equipment take this shit seriously because what manufacturer is going to sign off on something that’s farting and squealing because it’s being an antenna for the local AM radio station or courier dispatch radio room! It never ceases to amaze me that HiFi Audiophool types NEVER consider this. They would much rather believe that the $2000, 0.5M interconnect cable they’re looking at has had more thought and engineering put into it than the $50,000 amplifier they’re intending to hook it up to!

Internal Noise in Audio Circuits

This is quite a big subject and not something I’m going to go into detail here. If you want to bone up on it, here’s an excellent page: Link
Anyone who has owned a HiFi amplifier and has a little curiosity, will have turned up the volume to full with no input signal present. In this state, you will probably hear white noise and maybe the odd zizz or pop from local electromagnetic fields. Regardless of how much you paid for your amp, there will be noise produced by not only the components but also the movement of electrons in the conductors. Internal noise takes several different forms.

Thermal noise

Shot noise

Flicker (1 / f) noise

Burst noise

Avalanche noise

Noise generated by these factors is unavoidable in solid state audio circuits.

Noise Related to Digital Equipment

Things were simpler before digital. Before digital, HiFi was all about audio signals, starting tiny and then being amplified and disgorged from a pair of speakers. In the digital age, we have to deal with far more than this simple analogue landscape. Having a disc player, or worse, a DAC in your system unleashes a phalanx of egregious electromagnetic horror that could only be imagined in the vinyl era.
ESS_DAC.jpg


Let’s take the DAC, it’s basically an audio processing computer with HNKKKK! A clock oscillator! Oh the humanity… how will my musical goodness survive the RFI from the 9.5MHz clock oscillator??!?!?! Put simply, any potential interference has been designed out of the chip and the oscillator would have no ability to impinge on the audio signal. Take the ESS ES9038Q2M that sports a 128dB dynamic range and THD+N (Total Harmonic Distortion plus Noise) at -120dB. That’s noise folks, it’s at minus one hundred and twenty decibels, you can measure it but you can’t hear it.

Noise Related to Computer Network Equipment

Fantastically for snake-oil vendors, the advent of music streaming has given them yet another potential market for their hokey products. Recently, there was an entry in the “Extreme Snake Oil” thread relating to a network “switch” that had two ports, one input and one output. Just what is being switched here is anyone’s guess. Just for a lark, I posed as a customer with a fairly expensive setup and asked the vendors of the product how it will benefit my setup to have their switch in circuit. Their response was that it would eliminate “noise”, without going into any further detail. As I wrote in my “The Truth About HiFi Network Devices” post, modern Ethernet computer network devices have a robust design intended to reliably transmit data from one place to another. This has to be achieved in less than ideal environments where there could be a slew of other signals and electromagnetic fields present. Because of this, the designers of Ethernet chose to use twisted pairs of conductors for the critical functions of the system. This is to take advantage of “Common Mode Rejection” and is utilised in USB and balanced audio systems also.

Ethernet cable contains four pairs of wires which are twisted at different rates. Each half-twist of a pair acts like a mini-loop of wire; the orientation of a magnetic field relative to the wire is opposite in each half of the twist. This means any noise induced in the first half of the twist affects the wires in the opposite way in the second half of the twist, constantly cancelling itself out. The different rate, or pitch, at which one pair is twisted from the others ensures that any noise induced by the signal traveling through one pair can't affect any of the others. In USB cables, the D+ and D- signal wires carry a positive and negative version of the same information, respectively. So for each 1 coming down the D+ wire, a 0 is sent along the D- wire. At the receiving end, the D- signal is subtracted from D+, so any induced noise has its phase flipped and is cancelled out, leaving only the desired signal. Ethernet, USB and balanced audio cables all use variations of differential signalling to cancel the noise out of the signal.

In addition to the construction of the cable, an additional hardware noise mitigation is often applied to equipment. This network is known as “Bob Smith Termination” after its inventor and consists of a network of resistors, capacitors and centre-tapped secondary transformers.
bob-smith-1.png

By diverting some common-mode emissions to ground, you’ve effectively increased the system’s overall common-mode rejection ratio (CMRR). This means the return loss back to ground should be as low as possible.

Just as a brief illustration of the usefulness of the noise mitigation methods on Ethernet here’s a short account from out in the field.

“We ran a 300' Ethernet cable 15' below a 230KV power line. This was at a substation. Before the cable was grounded, (both ends floating) we measured 550 VAC (60Hz) to ground! Got some nice little zaps off of it. After grounding, we connected an AirFiber 24GHz radio, SNR was -28dB on all pairs.”

So to all the vendors flogging their HiFi network devices on the basis of “noise” reduction, I say “hogwash, bunkum and snake-oil!”

Shielding and Grounding.

We often hear the word “shield” or “shielding” in relation to HiFi cables, with this being some sort of high-end selling point. Shielding as such, is a mechanism to prevent spurious electromagnetic signals affecting the conductor within the shield. To achieve this, the shield is at ground potential and so any spurious energy is shorted to ground. In a common unbalanced cable, read “any RCA type” the best construction is coaxial where the signal wire (positive or hot) resides inside an all-encompassing outer conductor which is connected to ground. This can take the form of a sheath of small conductors wrapped around the insulation of the signal wire or a woven braid or foil. Some cables use a combination of a woven braid and foil.
GAC_10070.jpg

Interestingly, there aren’t a lot of unbalanced audio cables with braid and foil however if we we look at RF coax, this type of construction is very common. I balanced cable, the selection is vast but the primary difference in construction is that the balanced audio cable has a twisted pair encapsulated by the shield. As an aside, Ethernet cables have also adopted the shield concept in Category 6 cables and up (there’s actually a provisional Category 8 standard). The inclusion of a shield and drain wire is aimed at improving the SN ratio to achieve higher data speeds. In unbalanced circuits, the shield must be connected to the ground at both ends but with balanced cables, there’s an option to only connect one end of the shield to a ground. This method is called “shotgun shielding” and is primarily aimed at reducing the possibility of ground loops. As the shield is at ground potential with even one end grounded, it still performs the same function of grounding extraneous electromagnetic signals.

There’s nothing magical about shielding and the availability of stupidly over designed, over engineered cables does not change physics. Cables designed for professional use do not have fifteen layers of shielding made of pure, oxygen-free, directional unobtanium. No they just have shielding designed to ground the common interference signals from low frequency (braid) to RF frequencies (foil). Check these babies out for over engineered shielding! Link They even ship them in guitar cases :)
Gold-Audio-Cables-7-770x498.jpg


I’d just like to thank member Ken Tajalli for proposing a post on this subject. I have exceeded the scope of his suggestion somewhat and he has also taken me to task over some of the content (which he previewed). From here I’ll leave it up to the learned members to shred (if necessary) and add any wisdom of their own.
 

levimax

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Noise is an interesting subject, while it is certainly easier to hear than distortion how much it affects the enjoyment of listening to music seems to vary widely. Some people can't stand LP's because of the noise and others aren't bothered. Many of my favorite recordings, especially live recordings and some older recordings, have obvious noise during quiet sections yet it doesn't really bother me as long as the louder sections sound clean. For me noise is easily audible but not super important, I know for others "black background" is very important.
 

Waxx

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It would also be good to talk about the classic EMI/RFI filters in this article. I know what they do, but are not technical enough to make a clear explenation of it. But those, mandatory by electronic design rules in the EU (and also the US i think) are important, and they are cheap...

This is a classic circuit of such a filter.
1686642606814.png
 

fpitas

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It would also be good to talk about the classic EMI/RFI filters in this article. I know what they do, but are not technical enough to make a clear explenation of it. But those, mandatory by electronic design rules in the EU (and also the US i think) are important, and they are cheap...

This is a classic circuit of such a filter.
View attachment 291925
It's not required per se, but just like CE, the FCC sets limits on conducted and radiated emissions. With a power supply switcher or class D amp, you often end up needing an EMI filter.
 

restorer-john

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@Punter How about sitting the next couple of plays out?

Your endless 'truth about' threads are boring, superficial, tiresome, basically a poor man's version of ChatGPT and add no value to ASR.
 

fpitas

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Tough crowd. I think a lot of people enjoy them and learn a lot. It's one of the best things about ASR.
 

IPunchCholla

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@Punter How about sitting the next couple of plays out?

Your endless 'truth about' threads are boring, superficial, tiresome, basically a poor man's version of ChatGPT and add no value to ASR.
Maybe they are not meant for someone like you? It’s not like someone is tricking you into reading it. I personally have found them very helpful, in general.
 

Ken Tajalli

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@Punter How about sitting the next couple of plays out?
Your endless 'truth about' threads are boring, superficial, tiresome, basically a poor man's version of ChatGPT and add no value to ASR.
Its OK, a cup of coffee, or perhaps a couple (cases) of beer, would put you in a better mood. :)
I am with you, that this thread happened to be a little long-winded (boring?). I had a word in private with @Punter prior to creation of this thread, and my opinion was that:
Starting a "Truth about Noise" encompassing everything noise-related, well . . . . would be HUGE! My recommendation was to limit it just to "Ground-loop noise", but he was/is the boss, and he decided to do it his way.
At any rate, he puts a lot of effort into these. and more to the point, it encourages dialogue between the "Informed" and "not so informed".
That is how we learn stuff.
I rather have them, than not.
 

fpitas

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Since noise in all its forms is discussed in many threads here, it's hard to see why we should not have a thread to help the non-engineers understand.
 

Ken Tajalli

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Since noise in all its forms is discussed in many threads here, it's hard to see why we should not have a thread to help the non-engineers understand.
Yes true.
But I was of the opinion that the mentioned "ground-loop" is the least well-known.
Its creation and effects, is still misunderstood among many non-technicals.
 

restorer-john

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Since noise in all its forms is discussed in many threads here, it's hard to see why we should not have a thread to help the non-engineers understand.

Understand exactly what? It's an absolute train wreck of a thread.
 
OP
Punter

Punter

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I started off with the "truth About" thing to get some eyeballs on it and remember my first one was about power supplies. If you read along, I explained their form and function largely to debunk any malarky concerning fuses and power cables. I hoped some might like it for the technical explanation and others may enjoy having the ammunition on hand to counter any audiophool assertions about fuses and cables. The noise one was a bit of a lash up and I admit that I studiously ignored the advice of Ken Tajalli in writing it, even though it was his idea. I noticed myself veering from the subject but I just couldn't help myself, I really like the idea of ULF and VLF communications. Anyway, I did get the earth loop an shielding concepts across I think and hopefully some of the members got something out of it, As mentioned restorer-john, nobody's forcing you to read my posts if they're not up to the technical standard you believe they should be for the forum, I'd be more than happy to see you post something up that provides better or more accurate information.
 

Bob from Florida

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I started off with the "truth About" thing to get some eyeballs on it and remember my first one was about power supplies. If you read along, I explained their form and function largely to debunk any malarky concerning fuses and power cables. I hoped some might like it for the technical explanation and others may enjoy having the ammunition on hand to counter any audiophool assertions about fuses and cables. The noise one was a bit of a lash up and I admit that I studiously ignored the advice of Ken Tajalli in writing it, even though it was his idea. I noticed myself veering from the subject but I just couldn't help myself, I really like the idea of ULF and VLF communications. Anyway, I did get the earth loop an shielding concepts across I think and hopefully some of the members got something out of it, As mentioned restorer-john, nobody's forcing you to read my posts if they're not up to the technical standard you believe they should be for the forum, I'd be more than happy to see you post something up that provides better or more accurate information.

Not to "rain in your parade", but where does your background material for your many "truth about" threads originate from?
 
OP
Punter

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The background material is a combination of experience and research. I've been a broadcast tech for over 40 years and picked up a fair bit of knowledge over that time. I'm not a circuit designer, my work is primarily at a system level but back in the day, you had to have bench repair skills to component level as the gear you were dealing with had a substantial capital value to the operation. I've assimilated into the digital era but not to the same level as younger chaps who cut their teeth on it. As an old colleague of mine opined recently "we're analog techs in a digital age".
 

SSS

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The background material is a combination of experience and research. I've been a broadcast tech for over 40 years and picked up a fair bit of knowledge over that time. I'm not a circuit designer, my work is primarily at a system level but back in the day, you had to have bench repair skills to component level as the gear you were dealing with had a substantial capital value to the operation. I've assimilated into the digital era but not to the same level as younger chaps who cut their teeth on it. As an old colleague of mine opined recently "we're analog techs in a digital age".
Similar to me. I started as an radio/TV technician before studying EE. So at the former times component level repair was usage. What some digital thinking guys forget is that digital in detail IS analog. And there is some lack in understanding or better said "feeling" for analog circuits and components. This "feeling" is what the old guys developed over time and is helpful in resolving problems of noise, hum and EMI.
 
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