Why does better power = better sound?


Why does improving power quality improve sound quality?

I’m not asking to start an argument about power cords or wall outlets. Please let’s not go there. I’m asking because I’m hoping to learn some technical explanations for the effects of power quality on sound quality. I think I already understand how…

1. greater current availability = greater dynamic range
2. reduction of RFI/EMI = better signal to noise ratio

…but what about these…

3. ???????? = greater perceived resolution
4. ???????? = more realistic instrument timbres
5. ???????? = more precise imaging

Are differences in resolution, instrument timbres, imaging, etc. somehow reducible to current availability and/or powerline noise? If so, HOW are they reducible?

Again, I’m hoping to get into technical specifics, not polemical generalities.

Thanks in advance.

Bryon
bryoncunningham
Hi Bryon,

You're not there yet, but it is by no means hopeless :-)

My statement that:
The net voltage at any instant of time will be the NUMERICAL SUM of the individual amplitudes (voltages) of each frequency component at that instant of time
had nothing to do with intermodulation distortion, or with the sum and difference frequencies that intermodulation distortion results in. It was simply a description of the voltage at any instant of time of DC that is noisy.

As long as they are reasonably small, fluctuations in the DC voltages will IN THEMSELVES have no effect on anything. It is only when the frequency components corresponding to those fluctuations combine with the signal that a problem arises. The DC will not combine with the signal (in a properly functioning circuit). But the noise frequencies might, because they can couple from one circuit point to another via the various means I described.

Envision a musical note consisting of a 1 kHz fundamental frequency, and a harmonic of lesser amplitude at 9 kHz. (A real musical note would contain many other harmonics as well, such as 2 kHz, 3 kHz, etc. but I'm simplifying). And imagine that a noise frequency of 11 kHz, having some small but significant amplitude, couples onto that signal.

So far all that has happened is that a small 11 kHz signal has been added on to the signal having 1 and 9 kHz frequency components. That is probably not a major issue, assuming that the amplitude of the 11 kHz is not too great.

Now envision that the signal containing those three frequency components is passed through an amplification stage that has some degree of non-linearity, meaning that its output is not perfectly proportional to its input. Intermodulation caused by that non-linearity will result in many new frequencies, corresponding to the sums and differences between those three frequencies, and various other multiples of them. Perhaps most significantly, a 2 kHz frequency will be created as a result of intermodulation of the 9 and 11 kHz components. (20 kHz will also be created, among other new high frequencies, but that is obviously less significant). To the extent that the amplitude of that 2 kHz frequency is significant, it will alter the perceived timbre.

Now envision that a real-world musical note is present, consisting of a great many frequency components, and that noise also present, consisting of vastly more frequency components. Put all of that through a significant non-linearity and what you have is an unpredictable mess, having sonic attributes that can probably differ from those of the original signal in just about any way that is imaginable, including resolution, timbre, and imaging.

Best,
-- Al
04-26-12: Almarg
My statement that:

...the net voltage at any instant of time will be the NUMERICAL SUM of the individual amplitudes (voltages) of each frequency component at that instant of time...

had nothing to do with intermodulation distortion, or with the sum and difference frequencies that intermodulation distortion results in. It was simply a description of the voltage at any instant of time of DC that is noisy.

Got it! That clears up the confusion (mine, not yours). I was just thrown when, for some reason, I thought you were talking about the frequency intermodulation of DC voltage and noise. Sorry for my misunderstanding!

Your subsequent explanation of frequency intermodulation is very well described, and something I feel like I understand at the level at which you describe it.

What still remains a bit murky to me, as I mentioned in my last post, is the explanation of intermodulation at the level of voltage/current. Is intermodulation better understood as a fluctuation of voltage or a fluctuation of current? I understand that you can't change one without changing the other (Ohm's law), so maybe that question is meaningless. I would just like to have a better mental picture of what those electrons are doing! :-)

Bryon
Bifwynne,

I got my PF15i from Audio Advisor as an "open box" item (look under their clearance section) for $519. The box had indeed been opened but I'd swear it had never been out of the plastic wrap inside. I suspect "open box" is a ploy to get around manufacturer restrictions.
Is intermodulation better understood as a fluctuation of voltage or a fluctuation of current? I understand that you can't change one without changing the other (Ohm's law), so maybe that question is meaningless. I would just like to have a better mental picture of what those electrons are doing! :-)
It's best to think of everything I have described in terms of voltage. The current at any given point in the signal path is what it is, based on Ohm's Law.

One reason that all of this tends to be confusing is that the statement which is sometimes seen that the power supply is in the signal path, since it supplies the current that drives the next component in the chain, is a bit misleading.

Yes, in addition to powering the internal circuitry of an amplifier the power supply supplies the current that drives the speakers (supplying it via the transistors or tubes + transformer in the output stage of the amplifier). But a better way to think of it, IMO, is that the output stage of the amplifier will generate a voltage that at any instant of time is (to a close approximation) proportional to the voltage at the input of the amplifier at that instant (actually, slightly before that instant, because it takes a very small but non-zero amount of time for the signal to propagate through the amplifier). The power supply will then provide to the output, via the output transistors or tubes + transformer, whatever amount of current is necessary to establish that output voltage across the load resistance or impedance, consistent with Ohm's Law.

Best,
-- Al
...the output stage of the amplifier will generate a voltage that at any instant of time is (to a close approximation) proportional to the voltage at the input of the amplifier at that instant... The power supply will then provide to the output, via the output transistors or tubes + transformer, whatever amount of current is necessary to establish that output voltage across the load resistance or impedance, consistent with Ohm's Law.

That is very helpful, Al, and different from how I was thinking about it. Thank you for your heroic patience while explaining these things!

Bryon