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Hunt for RFI offenders


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19 minutes ago, Don Hills said:

(*) Old timers may remember when equipment such as computers used to have metal "finger" springs along the edge of the panels, which formed a continuous connection along the joins when the panels were closed. 

 

The same applies to most metal rack cases too ! You need to remove the anodising around the screw holes in the side and top panels , as well as around any earthing points.

 

How a Digital Audio file sounds, or a Digital Video file looks, is governed to a large extent by the Power Supply area. All that Identical Checksums gives is the possibility of REGENERATING the file to close to that of the original file.

PROFILE UPDATED 13-11-2020

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30 minutes ago, Don Hills said:

 

Computers usually used in domestic situations are exceptionally "permeable". 

The biggest problem is the aforementioned "slots". Slots are good aerials / antennas, acting as dipole radiators. A slot will form anywhere there is not continuous metallic contact between panels. (*)

Side access panels make poor contact along most of their edges, forming slots.

Grilles are usually only bonded to the cabinet at the corners, forming slots along the edges. The metal covers on the back panel covering the card slots usually only make good contact with the case at the ends. And ventilation slots are, well, slots.

 

(*) Old timers may remember when equipment such as computers used to have metal "finger" springs along the edge of the panels, which formed a continuous connection along the joins when the panels were closed. 

All true, though I assumed he meant permeable by design, maybe incorrectly. Within reason computers are designed not to care much about external influences, which are usually small compared to their 'self-created  and 'real close up' RFI.

 

At IBM we didn't give a rats ass about external RFI. We were far more interested in the operators dropping cigarette ash on the  'open' disk packs  as they inserted and removed them.  Later on we found that   didn't matter  much either :D 

 

What shielding there is on 'home' computers is more about passing 'RF radiating' regulations than anything else.

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1 hour ago, Em2016 said:

 

WiFi and bluetooth?

Of course, though the WiFi  (and presumably Bluetooth) frequencies are so far away from what our equipment can respond to that they couldn't  have any audible effect.

 

I'm no great expert of RFI, I just used to do some testing in  a hopefully RFI free environment which we could gradually increase to a large  but controlled amount.

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1 minute ago, Spacehound said:

Of course, though the WiFi  (and presumably Bluetooth) frequencies are so far away from what our equipment can respond to that they couldn't  have any audible effect.

 

I'm no great expert of RFI, I just used to do some testing in  a hopefully RFI free environment which we could gradually increase to a large  but controlled amount.

 

No worries. The post above was just sharing from one expert but that's only one data point. Experts always disagree and that's cool.

 

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3 hours ago, Em2016 said:

WiFi and bluetooth?

Those usually use either external antennas or foil antennas behind a plastic patch in the case.

 

BTW, I recently took apart a Marantz AVR. There were copper clips, copper foil, and copper-plated screws aplenty ensuring good connection between all chassis parts.

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5 minutes ago, Em2016 said:

 

Yup, in this case the housing is designed to be "permeable"

They do that on toy plane radio control too.

It operates nominally on 2.4 GHz but frequency hops about 1000 times a second  and also uses 'spread spectrum' so you can't really say it works at a particular frequency. Due to the 'spreading' its transmissions are  below background level so cannot be detected, but that's an 'accidental' side effect. 

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10 hours ago, Spacehound said:

And as has been pointed out, RFI is so far outside the audio band, and the usual frequency response of amplifiers etc. that it simply won't have any effect.

Well no, it can have a great effect. Many people have noticed that a cell-phone at 2GHz can affect their hi-fi system. So can old citizen band and police radio transmissions. While they don't go thru the system the same way the audio signal does, they can impact the feedback loop or bias.  When you look at a schematic in the back of a manual, it represents the circuit at audio frequencies, but high frequency interference will see the circuit differently.

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18 hours ago, Spacehound said:

A personal example:  I use a totally 'untweaked' Lenovo tower PC with an i7 processor, three spinning disks, and a fancy graphics card, so it is quite high on the 'RFI scale'. It's in the next room and the cables go though a hole in the wall so  it's inaudible. There are no  little 'improvers' anywhere and it's connected by USB  and Ethernet  cables from the local supermarket as my thirty years plus in the computer industry tells me that 'special' cables for digital working are a complete waste of money.

I use  big Tannoy dual concentric speakers so if take the grille off and  put an ear in one  I can hear all frequencies.

And there's a permanent WiFi signal  from the internet router that covers the whole house and most of the garden, maybe all of it.  And a couple from the neighbors too.

The 'worst case' for a test is JRiver playing 'silence' (which produces the same bit stream voltagewise  as a full orchestra or whatever at full throttle) and the amp at full volume. I hear nothing at all  from the speaker my ear is in  (and my hearing is  tested regularly for 'professional' reasons.)

 

And again, people just don't get it about what the impact of interference is on a digital rig - there's this concept that the interference generates an "extra noise", which one can hear as something distinct, over the speakers. Ummm, it just doesn't work this way - to this day I have never ever heard interference in this manner, unless I do something extremely savage like creating an arcing mains power link, close by.

 

What actually happens is that the quality of the reproduction is degraded - the sparkle, bite and life of the music gets dragged down, it becomes boring and listless to listen to - a "good" recording becomes, a "bad" recording. Of course, if one is not aware of what's happening, the easy out is to state the "bleedin' obvious" - gee, I didn't realise I had so many poor recordings ... :P.

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14 hours ago, Spacehound said:

...

At IBM we didn't give a rats ass about external RFI. We were far more interested in the operators dropping cigarette ash on the  'open' disk packs  as they inserted and removed them.  Later on we found that   didn't matter  much either :D 

 

What shielding there is on 'home' computers is more about passing 'RF radiating' regulations than anything else.

 

23 years at IBM, myself...

There was the trick of putting an AM radio on top of the CPU, then running a program that ran various delay loops to generate musical tones.

There was no smoking in the computer rooms I frequented as a condition of the Maintenance Agreements, but I agree there was plenty of opportunity for contaminants to get in. I recall an operator putting a pack in a drive, lifting off the cover then sneezing mightily before closing the drive. One of my jobs as an engineer was to clean packs and heads.

 

Home computer shielding is a bit of a joke, especially with the fashion for windows in the cases to show off the tech. Manufacturers have had to resort to tricks like spread spectrum clocking to get the EMI down to allowable levels.

Most of it is at frequencies too high to have any possible effect on audio equipment, though.

"People hear what they see." - Doris Day

The forum would be a much better place if everyone were less convinced of how right they were.

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16 hours ago, esldude said:

I have.  I posted files of music with noise added at different levels asking people to listen at their normal level and say when it disappeared.  Almost everyone heard it until -70 to -75 db and couldn't hear it below that. 

 

Thx - this was injected via the regular inputs?

 

not via RF thru the case to the circuits...??

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17 minutes ago, Ralf11 said:

 

Thx - this was injected via the regular inputs?

 

not via RF thru the case to the circuits...??

I actually simply added it to otherwise clean musical files.  So it isn't a test of how much RF can get thru devices.  Just a test of how much noise would have to result in it being heard. 

 

I have done things like wrap XLR cables around a high power switching PC supply.  Nothing came thru.  With RCA connection some noise did result at a mildly audible level.  Moving the RCA lines away 18 inches was enough to drop it below -130 dbv levels.  

And always keep in mind: Cognitive biases, like seeing optical illusions are a sign of a normally functioning brain. We all have them, it’s nothing to be ashamed about, but it is something that affects our objective evaluation of reality. 

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10 hours ago, Speedskater said:

Well no, it can have a great effect. Many people have noticed that a cell-phone at 2GHz can affect their hi-fi system. So can old citizen band and police radio transmissions. While they don't go thru the system the same way the audio signal does, they can impact the feedback loop or bias.  When you look at a schematic in the back of a manual, it represents the circuit at audio frequencies, but high frequency interference will see the circuit differently.

They certainly can get in from the speaker leads and the NFB path.

Even analogue TV transmitters 2KM away could cause "Frame Buzz" to be heard.It was possible to identify the TV station by watching for bright scene changes. The cure was looping the speaker leads through a large toroid.

 

How a Digital Audio file sounds, or a Digital Video file looks, is governed to a large extent by the Power Supply area. All that Identical Checksums gives is the possibility of REGENERATING the file to close to that of the original file.

PROFILE UPDATED 13-11-2020

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3 hours ago, esldude said:

I actually simply added it to otherwise clean musical files.  So it isn't a test of how much RF can get thru devices.  Just a test of how much noise would have to result in it being heard. 

 

I have done things like wrap XLR cables around a high power switching PC supply.  Nothing came thru.  With RCA connection some noise did result at a mildly audible level.  Moving the RCA lines away 18 inches was enough to drop it below -130 dbv levels.  

 

Thx - Let's go with 75 dB down then

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4 hours ago, Don Hills said:

 

23 years at IBM, myself...

There was the trick of putting an AM radio on top of the CPU, then running a program that ran various delay loops to generate musical tones.

There was no smoking in the computer rooms I frequented as a condition of the Maintenance Agreements, but I agree there was plenty of opportunity for contaminants to get in. I recall an operator putting a pack in a drive, lifting off the cover then sneezing mightily before closing the drive. One of my jobs as an engineer was to clean packs and heads.

 

Home computer shielding is a bit of a joke, especially with the fashion for windows in the cases to show off the tech. Manufacturers have had to resort to tricks like spread spectrum clocking to get the EMI down to allowable levels.

Most of it is at frequencies too high to have any possible effect on audio equipment, though.

Now you mention it I remember hearing about that radio trick.

 

And of course they weren't supposed to smoke, but our operators on night shift, when there was nobody about, certainly did.  And at    IBM France they did it openly - you won't stop the French smoking wherever they want. I used to be a member of the 'cable laying team' at weekends, three or four hours work Saturday or Sunday morning and then down to the local pub (we were in the 'country', close to a small village).  We crawled about under the false floors in the computer rooms making changes. And under the operating consoles there was always a pile of cigarette ends where the ops had put them through the grilles.

 

Incidentally, as we never bothered  to pull unused cables out as they were  all tangled up, the layer of cables got thicker and thicker and the space became less and less. As a development lab  we were constantly changing things around. At the time the main computer room at Hursley, UK, was the biggest computer room in Europe.

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7 hours ago, fas42 said:

 

And again, people just don't get it about what the impact of interference is on a digital rig - there's this concept that the interference generates an "extra noise", which one can hear as something distinct, over the speakers. Ummm, it just doesn't work this way - to this day I have never ever heard interference in this manner, unless I do something extremely savage like creating an arcing mains power link, close by.

 

What actually happens is that the quality of the reproduction is degraded - the sparkle, bite and life of the music gets dragged down, it becomes boring and listless to listen to - a "good" recording becomes, a "bad" recording. Of course, if one is not aware of what's happening, the easy out is to state the "bleedin' obvious" - gee, I didn't realise I had so many poor recordings ... :P.

I'm with you on the 'analog' side. But you mention 'digital rigs'. Unless I'm misreading you we are in agreement on that too.

 

My 30 plus years in the computer trade tells me it's completely impossible. 'Digital' stuff doesn't 'degrade', it works perfectly up to a point, and beyond that it just stops. And in a digital environment noise doesn't 'add up'.

 

Bits don't 'travel though the system'  like an analog signal does, where each signal is an 'as accurate as possible' reproduction of the previous one, brand new  bits are created at every point depending on what the received  one was, it's not a 'copy' of the received one. and that's true of the  USB (or whatever) transmitter - the DAC receives a bright shiny string of brand new bits. And it doesn't 'use'  those either, the bits coming out of the DACs USB receiver are brand new ones created BY the DACs USB receiver .'

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37 minutes ago, Spacehound said:

I'm with you on the 'analog' side. But you mention 'digital rigs'. Unless I'm misreading you we are in agreement on that too.

 

My 30 plus years in the computer trade tells me it's completely impossible. 'Digital' stuff doesn't 'degrade', it works perfectly up to a point, and beyond that it just stops. And in a digital environment noise doesn't 'add up'.

 

Bits don't 'travel though the system'  like an analog signal does, where each signal is an 'as accurate as possible' reproduction of the previous one, brand new  bits are created at every point depending on what the received  one was, it's not a 'copy' of the received one. and that's true of the  USB (or whatever) transmitter - the DAC receives a bright shiny string of brand new bits. And it doesn't 'use'  those either, the bits coming out of the DACs USB receiver are brand new ones created BY the DACs USB receiver .'

 

Possibly misreading ... I'm talking about any system that relies on the music source being stored in digital form - that data, while being considered as bits, is always fine - as you say. The troubles arise in the conversion to analogue, and anywhere from that point on. Those systems which are full analogue - tape, vinyl, etc - seem more immune to the particularly pernicious interference issues - hence, people talk of getting "analogue sound" ...

 

Further to that, I have a CDP here which is extremely flaky in pulling off CDR material - it struggles, the sound glitches like crazy at times, as the error recovery and interpolation circuitry does its best - but, it still manages to read the disk. So, the data integrity there is badly 'degraded', corrupted, from the interpolation - yet the music still comes through with full tonality ... I have no problems with even severe digital corruption, in terms of getting good sound.

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1 hour ago, Spacehound said:

and that's true of the  USB (or whatever) transmitter - the DAC receives a bright shiny string of brand new bits.

 

What is exported from the USB Port to the DAC is an ANALOGUE  representation of the digital data, and subject to the usual analogue vagaries due to the length of the cable, the isolation between D+and D-, and +5V Vbus and 0 volts, correct impedance of the USB cable, noise on the PC's internal +5V USB supply etc. Some longer USB cables don't even have shields, presumably done deliberately to  extend the operating distance of the cable  !!!

 

https://www.audiostream.com/content/draft?page=1

http://www.audiostream.com/content/theres-no-such-thing-digital-conversation-charles-hansen-gordon-rankin-and-steve-silberman-p

 

http://www.audiostream.com/content/qa-john-swenson-part-1-what-digital

http://www.audiostream.com/content/qa-john-swenson-part-2-are-bits-just-bits

https://www.audiostream.com/content/qa-john-swenson-part-3-how-bit-perfect-software-can-affect-sound

 

 

 

How a Digital Audio file sounds, or a Digital Video file looks, is governed to a large extent by the Power Supply area. All that Identical Checksums gives is the possibility of REGENERATING the file to close to that of the original file.

PROFILE UPDATED 13-11-2020

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43 minutes ago, sandyk said:

 

What is exported from the USB Port to the DAC is an ANALOGUE  representation of the digital data, and subject to the usual analogue vagaries due to the length of the cable, the isolation between D+and D-, and +5V Vbus and 0 volts, correct impedance of the USB cable, noise on the PC's internal +5V USB supply etc. Some longer USB cables don't even have shields, presumably done deliberately to  extend the operating distance of the cable  !!!

 

https://www.audiostream.com/content/draft?page=1

http://www.audiostream.com/content/theres-no-such-thing-digital-conversation-charles-hansen-gordon-rankin-and-steve-silberman-p

 

http://www.audiostream.com/content/qa-john-swenson-part-1-what-digital

http://www.audiostream.com/content/qa-john-swenson-part-2-are-bits-just-bits

https://www.audiostream.com/content/qa-john-swenson-part-3-how-bit-perfect-software-can-affect-sound

 

 

While I agree about it being analogue, it's a representation, as you say. It's not somethin that you have to amplify or whatever accurately.

Silberman is only a snake oil cable  manufacturer so I take no notice of him. As for  the others, Rankin talks  pure bollox at times. Swenson  is better but I think he is mistaken on some things.

 

Anyway, "appeals to authority", of which you seem so fond, are a logical fallacy because they  prove nothing either way.

 

 

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