Some quick truisms (with the disclaimer: all things held equal) ...
(1) When digital came in (PCM recording, CD, etc.), it gave "the industry" about 20dB more in headroom (over prev. generation analog/vinyl). Some say media companies abused this extra headroom by making albums louder (e.g., the loudness war, etc.). (See Bob Katz video links below)
(2) Less resistance in volume control (pot), means better SQ. (all things held equal)
.... ok, so knowing and accepting these two points ... does the audio signal stay more pure if the FULL range of, e.g., a rotary volume is used (because at the higher end, there is less resistance)? Again, all else held equal (so, ignoring ultimate impedance matching, etc.).
I'm asking this question in the context of the "loudness war" (see Refs) ... that some of the added clarity of a lower-level signal (vinyl, or loudness-free CD), is "simply" because listeners are using their volume control in its more-linear (= higher) range?
Refs:
Loudness war - Wikipedia, the free encyclopedia
The Loudness War - YouTube
Bob Katz about the "loudness war" part 1 - YouTube
Bob Katz about the "loudness war" part 2 - YouTube
(1) When digital came in (PCM recording, CD, etc.), it gave "the industry" about 20dB more in headroom (over prev. generation analog/vinyl). Some say media companies abused this extra headroom by making albums louder (e.g., the loudness war, etc.). (See Bob Katz video links below)
(2) Less resistance in volume control (pot), means better SQ. (all things held equal)
.... ok, so knowing and accepting these two points ... does the audio signal stay more pure if the FULL range of, e.g., a rotary volume is used (because at the higher end, there is less resistance)? Again, all else held equal (so, ignoring ultimate impedance matching, etc.).
I'm asking this question in the context of the "loudness war" (see Refs) ... that some of the added clarity of a lower-level signal (vinyl, or loudness-free CD), is "simply" because listeners are using their volume control in its more-linear (= higher) range?
Refs:
Loudness war - Wikipedia, the free encyclopedia
The Loudness War - YouTube
Bob Katz about the "loudness war" part 1 - YouTube
Bob Katz about the "loudness war" part 2 - YouTube
Your point 2 is false. Too little resistance increases distortion because it adds load to the previous stage.
You also may misunderstand how pots work. Assuming the usual log pot, then at the higher end (but not quite maximum) the impedance seen by the next stage is maximised. This is worst at -6dB attentuation (x0.5 in voltage). So at the higher end there is more resistance, not less.
Do some reading on potential dividers. Using the full range of a pot can reduce noise, as you are not putting the signal through successive stages of gain and attenuation. Apart from that there is nothing to worry about.
You also may misunderstand how pots work. Assuming the usual log pot, then at the higher end (but not quite maximum) the impedance seen by the next stage is maximised. This is worst at -6dB attentuation (x0.5 in voltage). So at the higher end there is more resistance, not less.
Do some reading on potential dividers. Using the full range of a pot can reduce noise, as you are not putting the signal through successive stages of gain and attenuation. Apart from that there is nothing to worry about.
I suspect this didn't happen because of the greater dynamic range offered by the CD format over vinyl. I doubt it's even so much an issue of maximum possible playback loudness, as that can be set as desired at home (within the physical limits of a given playback system) simply by adjusting the volume control knob.
It seems to me, that what CD may have done to contribute to the 'loudness war' was to establish a de facto standardized maximum playback signal voltage level of 2VRMS from CD source components. If the volume level is not changed somewhere after the 2VRMS CD source component level, then music content having an average level (ironically, by compressing the dynamic range) nudging up closest to the peak digital full-scale level will sound subjectively louder than music content registering that same peak level but having a lower average level (due to having an uncompressed dynamic range).
It's a music marketing issue, I suppose. For causal music listeners, which means everyone besides we few audiophiles, the louder perceived music will more readily grab the listeners attention, particularly in the bass.
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I'm not sure I fully understand the FULL interactive picture ... even DIY Tangent claims he never "got" volume controls -- but if the following stage is high impedance (ideal?), then shouldn't the vol. be low Z (or R)? Also, WRT to my orig. remark on lowest resistance and better SQ, I meant less stuff for the signal to go thru (ergo less noise) ... most pots (audio or not) are not boutique metal-film resistance-grade.
Just to clarify ...a question... for a typical log (audio) pot at max vol., what is a typical resistance that the audio signal (current) feels as it goes thru it?
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A low value resistor is not "less stuff" for the signal to go through. Circuits don't work like that.
A volume pot is an adjustable potential divider. Understand potential dividers and you are well on your way to understanding volume pots. They are actually quite simple; one of the simplest parts of any audio circuit.
A pot at max may present a few ohms in series with the signal and the full pot resistance in shunt to ground. A little below max (-6dB - a very small volume reduction) the source resistance seen by the following circuit (and any cable capacitance) is equal to a quarter of the pot resistance; all other volumes give smaller source resistance.
A volume pot is an adjustable potential divider. Understand potential dividers and you are well on your way to understanding volume pots. They are actually quite simple; one of the simplest parts of any audio circuit.
A pot at max may present a few ohms in series with the signal and the full pot resistance in shunt to ground. A little below max (-6dB - a very small volume reduction) the source resistance seen by the following circuit (and any cable capacitance) is equal to a quarter of the pot resistance; all other volumes give smaller source resistance.
E.g., Note in the this video how much more blue (resistive) area the current (signal) has to travel thru.
Then why do most preamps not include bass/treble? Why do better receivers and integrated amps have a bypass for tone controls?
Most certainly. We are inundated with unintentional music listening everywhere in the public sphere. At the shopping mall, in the office elevator, riding in a car, walking on the street, in public rest rooms. We are almost constantly exposed to background music it seems. So much so, that Gilberto's 'Girl from Ipanema' has become a background music cliche'.
I sometimes wonder whether the general apathy which younger generations show toward the focused and intentional listening activity that appreciation of an audiophile stereo system requires may partially stem from this constant exposure.
...And, here, you were thinking it was merely a humorous typo.
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I agree. I have walked out of shops because the task of being an acausal listener was too unpleasant.Ken Newton said:
A different issue. The problem (a quite tiny problem in most cases) is the accompanying active circuits, not the physical control with the knob on the end. All circuits add a little noise and distortion so if you don't need them omit them. The fashion for omitting tone controls has led some people to try to achieve tone control in a less convenient way by changing speakers, cables, preamps etc. A volume control cannot be omitted.hollowman said:
The physical size of a resistor tells us little. To the extent that it matters at all, a bigger resistor is likely to degrade the signal less. Don't learn your circuit theory from YouTube!
Learn how volume controls work (as I keep saying). Once you have got that, you could then look at tone controls - but they are more complicated.
DF96:
Respectfully, I understand vol. controls well enough to carry this discussion.
If you're suggesting that the total audible effect of vol. pot's resistive material is not significant (at least as far as the loudness war issue goes), I agree.
Nevertheless, one cannot simply ignore a variable-resistor fundamental: increase R, and you decrease I. Increasing vol. pot (counterclockwise) decreases resistance (and hence noisy, resistive material that the signal has to "swim" thru).
Lec 5 | MIT 6.002 Circuits and Electronics, Spring 2007 - YouTube
What is a resistor? - YouTube
Adding up resistance in series and in parallel - YouTube
Respectfully, I understand vol. controls well enough to carry this discussion.
If you're suggesting that the total audible effect of vol. pot's resistive material is not significant (at least as far as the loudness war issue goes), I agree.
Nevertheless, one cannot simply ignore a variable-resistor fundamental: increase R, and you decrease I. Increasing vol. pot (counterclockwise) decreases resistance (and hence noisy, resistive material that the signal has to "swim" thru).
Really?
Lec 5 | MIT 6.002 Circuits and Electronics, Spring 2007 - YouTube
What is a resistor? - YouTube
Adding up resistance in series and in parallel - YouTube
Three legs
Right, but you forgot about the WIPER (or are simply ignoring it): The current between the wiper and the hot end changes, as the wiper is moved.
I would add the following:
1) The value of volume pot is a key parameter in such an imaginary "inteface device", that includes the source (CD player) output connectors, interconnect cables with all their measurable and non-measurable artefacts, amp input connectors, volume pot with measurable and unmeasurable artefacts, wiring to the amp PCB input.
The "interface device" is in fact an inevitable additional "passive preamp" in any system.
2) This "passive preamp" interacts with the source (via output impedance) and with the amp (via input impedance).
3) The lower value of the volume pot, the better for amp (it works with almost resistive and low output impedance of "passive preamp"), the better for diminishing connectors and cables artefacts, and the worse for source (it is hardly loaded).
4) If source (CD player) has output impedance around 10 Ohms, is comfortable with low R loads, and has not lost good sound due to additional output buffer, then 600 Ohms - 1K volume pot (Penny&Giles for instance) will be definitely better for sound than any traditional non-professional audio pots 10-250 kOhms. This has been prooven by many, but in subjective listenings. Unfortunately, only very few CD players demonstrate such an ability (some Mark Levinsons for instance, with 5 Ohms output impedance). And, as always, one should look for the best compromise for a given system.
5) Quality of the pot itself - is an additional story.
1) The value of volume pot is a key parameter in such an imaginary "inteface device", that includes the source (CD player) output connectors, interconnect cables with all their measurable and non-measurable artefacts, amp input connectors, volume pot with measurable and unmeasurable artefacts, wiring to the amp PCB input.
The "interface device" is in fact an inevitable additional "passive preamp" in any system.
2) This "passive preamp" interacts with the source (via output impedance) and with the amp (via input impedance).
3) The lower value of the volume pot, the better for amp (it works with almost resistive and low output impedance of "passive preamp"), the better for diminishing connectors and cables artefacts, and the worse for source (it is hardly loaded).
4) If source (CD player) has output impedance around 10 Ohms, is comfortable with low R loads, and has not lost good sound due to additional output buffer, then 600 Ohms - 1K volume pot (Penny&Giles for instance) will be definitely better for sound than any traditional non-professional audio pots 10-250 kOhms. This has been prooven by many, but in subjective listenings. Unfortunately, only very few CD players demonstrate such an ability (some Mark Levinsons for instance, with 5 Ohms output impedance). And, as always, one should look for the best compromise for a given system.
5) Quality of the pot itself - is an additional story.
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I mean CLOCKWISE (not counterclockwise). My bad!
Back to the main issue ... anyone know what the resistive material is that's used in higher-quality pots?
I don't mean ...
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...In this case, the (more-resistive material) deleterious effects I'm proposing are almost a non-issue do to the discrete "channel" of each step. As the article indicates: "Each position has a specific value set of matched resistors. So at any point in the rotation of the shaft, you have pretty damn near the exact same resistance on both sides of the stereo signal. "
Oh, uh, I just had to add these in for challenged anal-retentives...
...Stereo Volume Controls
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The resistive material used for many high quality audio pots is called 'conductive plastic', which is some sort of rugged polymer that has carbon black added to it to make it conductive. I'm not an expert on how all conductive plastic pots are made, but I think that there are some that cast a uniformly conductive polymer into a track, sort of like the old Allen Bradley Type J carbon composition pots, but using polymers. What's more common for high end audio taper pots (especially those with custom or very precise tapers) is to use screen printing and other deposition techniques to add conductive polymers to an inert polymer substrate. Penny and Giles have made very nice linear conductive plastic faders in this way for decades, they sound great, and they are very rugged. Bourns and Clarostat have made some nice CP rotary controls for audio uses as well, but I'm not sure how they are constructed.
Still, pots suffer from a lot of potential evils. The wiper does not always make consistent contact with the resistive material, and the resistive material can sometimes be so granular that conduction through the track is a function of the applied voltage… not a good thing. Different designs do sound different, and IMHO, none are as nice as fixed value, high quality resistors, like those lovely Dale CMF60s on the rotary switch in the picture above! ;-)
Still, pots suffer from a lot of potential evils. The wiper does not always make consistent contact with the resistive material, and the resistive material can sometimes be so granular that conduction through the track is a function of the applied voltage… not a good thing. Different designs do sound different, and IMHO, none are as nice as fixed value, high quality resistors, like those lovely Dale CMF60s on the rotary switch in the picture above! ;-)
One further point ought to be made. You state that there is "noisy, resistive material that the signal has to "swim" thru". This is a necessary fact for any resistive material, in a pot, a wire wound resistor, a thin film resistor, or a carbon composition resistor.
In fact, this noise, Johnson noise, is completely predictable. It exists as a voltage density per root frequency, and the sum total noise over a desired bandwidth can be calculated as e-sub-n = sqrt(4*K*T*R*B) where K is Boltzmann's constant, T is the temperature of the resistor in degrees Kelvin, R is the resistance in ohms, and B is the bandwidth over which you want to determine the noise voltage that the resistor generates.
This is the minimum theoretic noise that a resistor must generate when it is at a temperature T. Sub-optimal resistors will generate additional noise when conducting a current, but the real component of the impedance of each and every circuit element, whether you think it's a resistor or not, will generate noise according to this formula. Note that the imaginary component of an impedance, i.e. the reactance, does not contribute noise… only the real component must generate this noise, independent of how this resistance is brought about. In other words, a pot, a photo-resistor, a piece of wire, an active circuit that generates a resistance, a piece of lettuce, etc. are all subject to this physical requirement.
In fact, this noise, Johnson noise, is completely predictable. It exists as a voltage density per root frequency, and the sum total noise over a desired bandwidth can be calculated as e-sub-n = sqrt(4*K*T*R*B) where K is Boltzmann's constant, T is the temperature of the resistor in degrees Kelvin, R is the resistance in ohms, and B is the bandwidth over which you want to determine the noise voltage that the resistor generates.
This is the minimum theoretic noise that a resistor must generate when it is at a temperature T. Sub-optimal resistors will generate additional noise when conducting a current, but the real component of the impedance of each and every circuit element, whether you think it's a resistor or not, will generate noise according to this formula. Note that the imaginary component of an impedance, i.e. the reactance, does not contribute noise… only the real component must generate this noise, independent of how this resistance is brought about. In other words, a pot, a photo-resistor, a piece of wire, an active circuit that generates a resistance, a piece of lettuce, etc. are all subject to this physical requirement.
If anyone has 'scope/noise traces -- or data charts -- illustrating/documenting the issue, please share if possible. This may better (dis)prove my pet less-noise-at-high-volume hypothesis. Note, that this hypothesis does not apply to...
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No. In a well-designed volume pot arrangement the current through the wiper is much smaller than the current through the resistor and so can be ignored.hollowman said:
Putting up a wrong idea and then asking for proof that it is wrong before discarding it is not generally a good method of increasing personal understanding of any technology. There are lots of wrong ideas for which there is no proof that they are wrong because they are so obviously wrong (to anyone with the necessary understanding) that no proof is needed and so no proof has been developed. The wrong ideas for which there is proof that they are wrong tend to be the more plausible wrong ideas which could, perhaps, have been true but actually are not.
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