Any technical minds know about cable capacitance?

[A Surfer]

I lack the technical knowledge to dig into the argument made that I will post below, but I was wondering if anybody who is technically adept could tell me if the arguments being trotted out by a cable believer is pure bunk which I suspect it is. Essentially this person is stating that the capacitance of audio cables can and will have audible effects. Specifically the poster on head-fi stated:
START ----->
Its not baseless at all. Capacitors are low-pass filters.
A high output impedance or using a passive preamp, followed by a high capacitance cable, will cause treble rolloff. This is not snake-oil, this is fairly basic EE.

You can see the measured effect here: https://www.superbestaudiofriends.o...uator-comparison-technical-measurements.7324/

Manufacturers of passive preamps will warn you of this too: https://tortugaaudio.com/what-is-a-passive-preamplifier/

And the audible effect? Well, try it for yourself. If you can't hear a several dB rolloff by 20khz then I don't know what to say.


The length of cables at concerts etc are an apples to oranges comparison. They are sourced from DACs with exceptionally low output impedance, specifically so that they do not encounter any issues in situations they were designed for. You aren't using a passive preamp or high output impedance DAC for a 100ft run at a concert.

END ------>

The link to the testing at SBAF is beyond my technical knowledge, but I do not believe that with any typical use scenario regular audio cables have any audible effect and roll-off treble due to capacitance. Am I wrong? Looking for some input on this from those who actually know enough to interpret the evidence the poster offered by way of the SBAF link out. Thanks to anyone who can help me with this as it goes beyond me.

 

[bigjacko]

If the capacitance is low enough, the high pass will happen at very high frequency way out of our hearing, eg 100kHz. There should be no worry about it since guarantee no one can hear them.

 

[MDAguy]

A high capacitance cable will probably act like a very very very high-pass filter/capacitor and therefore have no affect on 20hz to 20kHz..

 

[witchdoctor]

I lack the technical knowledge to dig into the argument made that I will post below, but I was wondering if anybody who is technically adept could tell me if the arguments being trotted out by a cable believer is pure bunk which I suspect it is. Essentially this person is stating that the capacitance of audio cables can and will have audible effects. Specifically the poster on head-fi stated:
START ----->
Its not baseless at all. Capacitors are low-pass filters.
A high output impedance or using a passive preamp, followed by a high capacitance cable, will cause treble rolloff. This is not snake-oil, this is fairly basic EE.

You can see the measured effect here: https://www.superbestaudiofriends.o...uator-comparison-technical-measurements.7324/

Manufacturers of passive preamps will warn you of this too: https://tortugaaudio.com/what-is-a-passive-preamplifier/

And the audible effect? Well, try it for yourself. If you can't hear a several dB rolloff by 20khz then I don't know what to say.


The length of cables at concerts etc are an apples to oranges comparison. They are sourced from DACs with exceptionally low output impedance, specifically so that they do not encounter any issues in situations they were designed for. You aren't using a passive preamp or high output impedance DAC for a 100ft run at a concert.

END ------>

The link to the testing at SBAF is beyond my technical knowledge, but I do not believe that with any typical use scenario regular audio cables have any audible effect and roll-off treble due to capacitance. Am I wrong? Looking for some input on this from those who actually know enough to interpret the evidence the poster offered by way of the SBAF link out. Thanks to anyone who can help me with this as it goes beyond me.

The post at Tortuga claiming passive preamplifiers can offer great value is correct:

https://www.audiosciencereview.com/...und-3-in-1-out-xlr-audio-switch-review.11062/

 

[Wombat]

Unless a 'passive preamp' has a step-up transformer, call it what it is. An attenuator, impedance matcher or switch box. It is not signal amplifier unless it goes into resonance.

 

[pma]

Output impedance + cable capacitance makes low pass filter, not high pass. The equation is

F(-3dB) = 1/(2*3.14*Rout*Ccable)

 

[boXem]

Output impedance + cable capacitance makes low pass filter, not high pass. The equation is

F(-3dB) = 1/(2*3.14*Rout*Ccable)

Indeed.

 

[Blumlein 88]

I lack the technical knowledge to dig into the argument made that I will post below, but I was wondering if anybody who is technically adept could tell me if the arguments being trotted out by a cable believer is pure bunk which I suspect it is. Essentially this person is stating that the capacitance of audio cables can and will have audible effects. Specifically the poster on head-fi stated:
START ----->
Its not baseless at all. Capacitors are low-pass filters.
A high output impedance or using a passive preamp, followed by a high capacitance cable, will cause treble rolloff. This is not snake-oil, this is fairly basic EE.

You can see the measured effect here: https://www.superbestaudiofriends.o...uator-comparison-technical-measurements.7324/

Manufacturers of passive preamps will warn you of this too: https://tortugaaudio.com/what-is-a-passive-preamplifier/

And the audible effect? Well, try it for yourself. If you can't hear a several dB rolloff by 20khz then I don't know what to say.


The length of cables at concerts etc are an apples to oranges comparison. They are sourced from DACs with exceptionally low output impedance, specifically so that they do not encounter any issues in situations they were designed for. You aren't using a passive preamp or high output impedance DAC for a 100ft run at a concert.

END ------>

The link to the testing at SBAF is beyond my technical knowledge, but I do not believe that with any typical use scenario regular audio cables have any audible effect and roll-off treble due to capacitance. Am I wrong? Looking for some input on this from those who actually know enough to interpret the evidence the poster offered by way of the SBAF link out. Thanks to anyone who can help me with this as it goes beyond me.

Yes at some not unreasonable lengths and the wrong gear it can cause a mildly audible roll off.

On the other hand, sure you can use it with a 100 ft cable. Just make sure the attenuator is at the end furtherest from the output of the source. I've made them in a little box that has a male RCA jack on one side and female on the other. Plug it directly into the input jack of the amp and you can use long cable lengths between there and the source.

 

[A Surfer]

Thank you everyone for chiming in. The head-fi poster was suggesting that keeping your interconnects as short as possible would matter audibly due to capacitance. I was suggesting that with normal length audio interconnects for home that there would be no audible effects due to the cable. Are people here saying that a run of the mill RCA interconnect that is 6 feet long may effect the sound audibly versus say a 2 foot length of the same cable?

 

[Speedskater]

For any reasonable coax RCA cable, a 2 foot cable and a 6 foot cable will sound the same. But a 50 foot cable may have more low frequency background noise than a 2 foot one.
With modern circuit design (low output impedance and high input impedance) the cable would have to be much longer than 50 feet before capacitance starts to matter. (with reasonable coax cables)

 

[DonH56]

Most active preamps have an output impedance around 100 ohms to perhaps 1 k-ohms, with some tube preamps higher. Typical coaxial interconnects have capacitance around 20~30 pF/foot.

Treating the cable as a lumped capacitance (not quite correct but good enough for this particular debate), and ignoring the cable resistance as much, much lower the the preamp's driving impedance, let's target 25 kHz for -3 dB, use the 1 k-ohm output, ignore the load (amp input -- it will extend the bandwidth a little), and choose 30 pF/ft for cables for a worst-case analysis:

Corner (-3 dB) frequency fc = 1 / (2*pi*R*C) so C = 1 / (2*pi*R*fc) = 1 / (2*3.14159*1000*25000) = 6.366 nF

Now c' = 30 pF/ft for the cable and so the length L of cable you can tolerate in this example is L = 6.366e-9 / 30e-12 = 212.2 feet.

If your preamp has 100-ohm output impedance you can tolerate 2122 feet.

Yes, it is a low-pass filter, but unless your room is exceptionally large it will not be a problem for you.

I am pretty sure this calculation has been done many, many times before on ASR and many other places.

If you are using a passive preamp (why?), then it is probably a potentiometer (variable resistor), and may be in the 10k-ohm to 100k-ohm range so indeed is a much higher resistance and will roll off much sooner. A good reason to not use one without a buffer. They will argue the buffer adds noise and distortion; true, but negligible. The most subjective "purists" always manage to ignore the gazillions of active devices in the recording path in their conclusion that their electronics must meet some completely unrealistic standard of excellence. The same folk who abhor room treatments, neglect speaker distortion, and disparage specifications as meaningless.

 

[watchnerd]

Essentially this person is stating that the capacitance of audio cables can and will have audible effects.

Capacitance is a legit concern with phono cables used with MM cartridges.

 

[DonH56]

Capacitance is a legit concern with phono cables used with MM cartridges.

True, but most cartridges are designed to work into typical cable capacitance and need a little extra in the preamp for a few (say 6' or under) of cable. If the TT is far from the preamp, like across the room, you may need to place the preamp closer to the TT. I have seen that a few times (even in my own system) and had to do a bit of rearranging to accommodate that setup.

I skimmed pretty quickly and did not follow the links, but it sounds like the situation was with a "passive" preamp, which is more sensitive to cable (and all other) capacitance.

 

[AnalogSteph]

With modern circuit design (low output impedance and high input impedance) the cable would have to be much longer than 50 feet before capacitance starts to matter. (with reasonable coax cables)

Emphasis on modern circuit design. "Passive preamps" may not qualify. You can generally get by with a 10k pot but any higher than that, and worst-case output impedance tends to get uncomfortably high. Everything based on transformers also tends to be tricky business... it is essentially impossible to meet typical max capacitive loading specs of 10k:10k jobs with typical line-ins (recently I saw one that specified 50 to 100 pF max - input filter capacitance alone tends to be 100-220 pF at least, not even accounting for any cable runs).

Capacitance is a legit concern with phono cables used with MM cartridges.

Indeed. Notoriously inductive buggers whose impedance magnitude tends to reach the double-digit kOhms towards the upper end of the audible range.

 

[watchnerd]

Unless a 'passive preamp' has a step-up transformer, call it what it is. An attenuator, impedance matcher or switch box. It is not signal amplifier unless it goes into resonance.

Wait, am I supposed to call this a 'passive preamp' now?

So confusing...

 

[watchnerd]

The post at Tortuga claiming passive preamplifiers can offer great value is correct:

https://www.audiosciencereview.com/...und-3-in-1-out-xlr-audio-switch-review.11062/

This picture from Tortuga is horrible though:

 

[Blumlein 88]

I'd note that -3 db at 25 khz will sound sightly soft to younger years.

 

[watchnerd]

I'd note that -3 db at 25 khz will sound sightly soft to younger years.

EHHH? WHAT WAS THAT?

CAN YOU SAY THAT AGAIN, SON?

 

[A Surfer]

I'd note that -3 db at 25 khz will sound sightly soft to younger years.

Really? They hear 25kHz with any amplitude? Even so, how much musical information is contained that high up and with appreciable amplitude?

 

[watchnerd]

Really? They hear 25kHz with any amplitude? Even so, how much musical information is contained that high up and with appreciable amplitude?

It's not a brick wall.

If it's a first order slope, it will still be down a few dB <20kHz.