Are passive volume controls totally transparent?

[Holmz]

Nobody wires a passive volume control as a series resistor when dealing with a high-impedance load, that would be silly. What you want is a variable voltage divider. Worst-case output resistance then becomes
Rout,max = (Rsource + Rpot)/4 ≈ Rpot/4 (assuming Rsource << Rpot)
which occurs at the -6 dB point.

Assuming a 4-gang 5 kOhm pot for a stereo balanced signal (equivalent to a stereo 10k when unbalanced), this means a worst-case output impedance of about 2.5 kOhms. In the face of typical 10-20 kOhm input impedance on the other side, this gives impedance levels that may be a tad high for long cable runs but should be just fine for the lengths required on your desk. The usual 1-opamp balanced receiver circuits with 10k/10k/10k/10k are barely going to notice an added 1.25k on each leg.

Did you miss the point that the resistor represents the output impedance of the device powering the cable?

 

[Miguelón]

Curious what interface you have to use? One could set it up as a buffer if you want to do so. Feed the DAC into it. Then onto the Genelecs.

I have a Focusrite Scarlett 2i2 4th gen; is noisier than my WiiM

For instance no issues with digital control on WiiM, at 40 dBFS it still sounds well. There’s noise but this is the typical Genelec hiss

 

[Blumlein 88]

I have a Focusrite Scarlett 2i2 4th gen; is noisier than my WiiM

For instance no issues with digital control on WiiM, at 40 dBFS it still sounds well. There’s noise but this is the typical Genelec hiss

I've sort of gotten lost. So what is the problem when you use the WiiM directly to the speakers?

 

[Miguelón]

I've sort of gotten lost. So what is the problem when you use the WiiM directly to the speakers?

Sorry, if you read carefully I never mentioned a problem.

The origin of the post was some perceptions and myths around passive volume or gain attenuators. They seem not well based on real facts though, as many beliefs in audio world.

My only personal concern was the fact that Genelec G Three has a different (easy to notice) sound with respect to 8030C that surprised me because equal measurements and attributed to the gain knob on the 8030C input.

The original question was answered, no difference should be noticed between a fixed attenuator of X impedance amp input and Y impedance output and a variable one with same X and Y values.

Believe me that I’ve seen a tone of questions or affirmations like that, the only one that appears to be true is that active preamps and buffers can leave intact the impedance of the circuitry.

 

[Miguelón]

I'm not either... that said the word seems is more appropriate than you might have intended.

In a practical sense 2 resistors as an attenuator and a half decent potmeter set to the same attenuation and of the same value might well measure a bit different in say S/N ratio and maybe frequency extension in the MHz range (so far, far above and below any audible thresholds) but are basically exactly the same.

Now... when one of the attenuators actually is not an attenuator but say gain control the measured differences could be bigger (distortion/noise/frequency range) but likely not reach audible levels either.

Hy @solderdude, I’ve just have a patient who is audio engineer and built some speakers to a local brand here in Galicia (Spain). He was so gentle to listen to my question about my perception of home vs pro versions of Genelec.

He told me that is a common practice to add some electronics to “decorate” a little the nude sound of a very clean amp-speaker: usually adding harmonics or little ringing to have a better feel without touching the FQ, directivity or undesired harmonics.

As you mentioned, gain knob nor attenuators influence at all those kind of speakers, but he said that about all probability if there’s a difference is totally intentioned.

He didn’t negate the possibility of a psychological effect, but he told me that the most trustable in terms of neutral coloration should be the professional version, the opposite is a nonsense as 8030C is well known as a reference monitor.

 

[antcollinet]

I have an audio interface, feeding the input with output of DAC, recording and analyzing and then comparing with DAC through monitor passive controller should show if are a significant difference.

Am I correct? What software should I use to see the harmonics?

Not everything is harmonics. Don't be the craftsmen who has just discovered hammers, and thinks every problem is a nail.

Harmonics are about non-linear distortion. Passive volume controls do not create distortion. As @Blumlein 88 has pointed out above IF you have a long cable after the volume control, the capacitance of this can result in a rolloff of the high frequencies. This would be measurable on a frequency response plot if it were audible.

In either case, you can use REW to measure distortion or frequency response.

 

[ZolaIII]

No they are not transparent, analog pots go off at beginning and close to the end. So you put it in the middle usually marked as 0 dB (and represents value with which when feed with specified gain they reach specified maximum output power) and instead control the input V digitally in feeding and processing end and on the FP which is then send to DAC and glued back to 32 bit integer (or 24 bit on older one) which they operate on. You limit input gain to the calibration point and to protect equipment and let 100 0.5 dB steps or more linear V controls to take over. Even when you really try to put the speakers on equal distance and try to get ideal placement and matching their SPL there will still be a difference in starting impulse timing (they won't be on exactly same distance). And I believe you're wife do to her job can hear it. It can be corrected with convolution as FIR or IRR impulse correction.

 

[Miguelón]

No they are not transparent, analog pots go off at beginning and close to the end. So you put it in the middle usually marked as 0 dB (and represents value with which when feed with specified gain they reach specified maximum output power) and instead control the input V digitally in feeding and processing end and on the FP which is then send to DAC and glued back to 32 bit integer (or 24 bit on older one) which they operate on. You limit input gain to the calibration point and to protect equipment and let 100 0.5 dB steps or more linear V controls to take over. Even when you really try to put the speakers on equal distance and try to get ideal placement and matching their SPL there will still be a difference in starting impulse timing. And I believe you're wife do to her job can hear it. It can be corrected with convolution as FIR or IRR impulse correction.

I can hear it also, but 8030 is very very sensitive to manage at 0 dB, as it produce 100 dB SPL at this sensitivity. My audio interface pot has also a mid-point optimal position advised by the brand: between 10:30 and 19:30 or something like that.

The home version of the 8030C has an extra protection against clipping by being adjusted at -10 dB less sensitivity but still high enough to clip because of current use of 4 or more volts on home gear.

Hopefully I’m using a 2 volt DAC so at is quite improbable to saturate the amp

 

[solderdude]

channel imbalance has nothing to do with 'transparency' but is about balance.
And yes, usually the lowest volume settings have the highest imbalance and is very 'device' dependent.
Transparency is about signal fidelity not about balance.

 

[Miguelón]

What make me curious is why they exist so much chaos in inputs and outputs…

Is not easier to establish a convention (say 2 volts or 1 volts, or whatever) to lines and stay with it?

 

[antcollinet]

Is not easier to establish a convention (say 2 volts or 1 volts, or whatever) to lines and stay with it?

Well that would certainly be nice.

The answer is "history", and "its just not that simple"

 

[mhardy6647]

Impedance.
Is important.

 

[antcollinet]

Impedance.
Is important.

But....

RESISTANCE IS FUTILE.

 

[Miguelón]

Well that would certainly be nice.

The answer is "history", and "its just not that simple"

Yep, another thing that makes me crazy (and with all my respect to your country) is the existence of metrics convention in meters/ kilograms / seconds and at same time yards / pounds…

But this is an audio thread, fortunately volts are volts and dB is dimensionless, if not we will fight to express sound pressure in pound per square inch or in newtons per meter square

Again, excuse me, not intended to offend

 

[Miguelón]

But....

RESISTANCE IS FUTILE.

 

[antcollinet]

if not we will fight to express sound pressure in pound per square inch or in newtons per meter square

Personally I prefer Long Tons per acre.

Again, excuse me, not intended to offend

None taken.

 

[Blumlein 88]

Yep, another thing that makes me crazy (and with all my respect to your country) is the existence of metrics convention in meters/ kilograms / seconds and at same time yards / pounds…

But this is an audio thread, fortunately volts are volts and dB is dimensionless, if not we will fight to express sound pressure in pound per square inch or in newtons per meter square

Again, excuse me, not intended to offend

Pascals. 1 pascal is 94 db SPL.

 

[Miguelón]

Pascals. 1 pascal is 94 db SPL.

Poor Pascal, Torricelli and others… I think pressure is one of the most maltreated units: Barrs, Pascals (newton per square meter IRC), atms, psi, …

 

[mhardy6647]

But....

RESISTANCE IS FUTILE.

Let the record show: I am rolling on the floor here.

 

[Miguelón]

Let the record show: I am rolling on the floor here.

So well deserved