For that mater it is also close to 6th for ntsc . However it is only as I understand it generated when processing signal . May be a sub harmonic generated by the converters of the osc freq. Not sure . A problem that should note be disregarded easily .
For that mater, tons of lab equipment are using 15.625Hz line frequency in their displays. We have here an Agilent 54750A 20GHz digital scope which is radiating the hor. line frequency at -80db, on a dynamic signal analyzer, from 10ft. away. It's fun to move the DSA cables around and watch the spectra pulsing up/down, usually the scope user gets some nasty flak about 100 pound dinosaurs.
OTOH, I'm using a Tek 3052 500MHz shoebox scope and the LCD CFL power supply radiates at some 60KHz so badly that occasionally it triggers the scope. No need to mention what this means for a short memory cheapo digital scope.
The fight-club show of tonight is boring, don't you find ? A bad B-Show. There is no better position on one side than an other. Trying to approach perfection in audio reproduction imply BOTH good engeneering and careful choice of components, BOTH measurements and carefull listening. And a good audio designer will dedicate his life to increase BOTH his knowledge and accuracy of his listening ability. Because there are things we can measure, and things we cannot, with our actual instruments, but that we can 'feel'.
Nothing is 'enough', we have to try our best.
Nothing is 'enough', we have to try our best.
i don't want anyone to take the data shown too literally or to try to guess what the cause is. For one thing the signal has been attenuated 20X to prevent loading of the source. Same for this one here ......
Just after 100KHz, the noise level goes way up out to >500Khz. This is a BlueRay playing video test disk only and the output of one audio channel shown. The player also has an idle freq at 950Khz.
There is no broad band of noise freqs until it is in Play mode.
There are many, many out-of-band signal sources getting into our audio.... from the equipment itself onto the ac lines; thru EMI/RFI and digital and video gear. And, to some extent, every system is in a different environment. But, clearly the out-of-band energy ought to be addressed for analog signals.... if you want the lowest system distortion.
THx-RNMarsh
Just after 100KHz, the noise level goes way up out to >500Khz. This is a BlueRay playing video test disk only and the output of one audio channel shown. The player also has an idle freq at 950Khz.
There is no broad band of noise freqs until it is in Play mode.
There are many, many out-of-band signal sources getting into our audio.... from the equipment itself onto the ac lines; thru EMI/RFI and digital and video gear. And, to some extent, every system is in a different environment. But, clearly the out-of-band energy ought to be addressed for analog signals.... if you want the lowest system distortion.
THx-RNMarsh
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Of course, Richard and Esperado are correct. High frequency 'garbage' has been around virtually forever, and it is not getting better.
Waly, if you don't believe in improving audio quality, why do you bother us here?
For the record, it is difficult to make a low pass filter that will not be ACTIVE and therefore prone to adding distortion. It is simply easier to make audio gain stages that can handle high frequency 'garbage' and rely on a simple RC rolloff above 100KHz to reduce any real RF. It doesn't cost that much more, maybe a slightly faster IC will do it. Even better, a true class A discrete design.
Waly, if you don't believe in improving audio quality, why do you bother us here?
For the record, it is difficult to make a low pass filter that will not be ACTIVE and therefore prone to adding distortion. It is simply easier to make audio gain stages that can handle high frequency 'garbage' and rely on a simple RC rolloff above 100KHz to reduce any real RF. It doesn't cost that much more, maybe a slightly faster IC will do it. Even better, a true class A discrete design.
Because he's a smart and knowledgeable guy, and not once stated it can't be improved ?
I would try a few ferrites (SMD 0603 for example) in series with the output - right at the connector and then from the connector after the ferrite a small cap to ground - say 100 to 200 pF.
Have you tried a common mode clam ferrite on the power cable? I lot of these BD players use SMPS that may be responsible for noise in the 100kHz to 1MHz region as well.
[uh oh . . . the Sandman commeth 😉 ]
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I think that's for resistors - the ferrite devices DC and LF resistance is extremely low - a few ohms. I am not aware that that is modulated by the signal current which should be quite low (uA range).
More often than not, its HF very much higher up on F that is getting demodulated in the input stages that is the problem.
However, an RC pad on the input is a good thing. If you set it for c. 200kHz, you are only down 0.1dB at 20 kHz and 40 dB down at 20 MHz
audiophiles are very suspicious of lossy ferrites, ferrite cores
a "story" is that they saturate and afterwards cause added distortion
super sizing (aka "engineering for the application, expected worst case...), selecting better materials for the function, dealing with material, geometry limits on effective performance all might be a help
and I don't know if John has noticed but mid 90's is now 2 decades ago - from then and moving forward there has been major change in op amp offerings - we have quite substantially better, faster Semi processes and op amps designed on them for more demanding telcom, medical imaging requiring good performance to MHz
a "story" is that they saturate and afterwards cause added distortion
super sizing (aka "engineering for the application, expected worst case...), selecting better materials for the function, dealing with material, geometry limits on effective performance all might be a help
and I don't know if John has noticed but mid 90's is now 2 decades ago - from then and moving forward there has been major change in op amp offerings - we have quite substantially better, faster Semi processes and op amps designed on them for more demanding telcom, medical imaging requiring good performance to MHz
Not before you would agree to breath and live by the First Principles. Till then, we don't have a common language to communicate.
But you don't need me, you already got it right 40 years ago. Nothing happened since, at least not as far as you (and other famous designers) are concerned.
Yes you've got it! Unfortunately AM radio starts at 540 kilohertz around here and we have 50 kW two miles away. The issue with RC is the series R adds noise and the C often self resonates. (Some power supply electrolytic's actually resonate in the audio band!)
The issue of attenuating just above the audio band effectively requires L & C if you want to do it passively. L comes with serious penalties, either over size air core and large loop area or distortion from a core material. So wider bandwidth in the amplifier and making it an active filter is one way to go.
Bipolar junction transistors as input devices can be a real problem, particularly when current starved.
So a JFET input with a wideband amplifier that has active filtering is one good approach. Of course JFETS are not where the money is for most manufacturers.
So my next project should be a time machine to allow purchasing the best parts that are now no longer made. 🙂
FTR, I wasn't suggesting doing 80dB rejection at one octave removed, just that having bandwidth (traditionally defined by -3dB points) much beyond 20kHz can only have bad effects. I get very suspicious when audio designers put out things like amps that are flat to MHz.
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