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Old 18th Jun 2021, 7:53 am   #2361
dglcomp
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Default Re: The Audiophoolery Thread.

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We were at an Eagles concert pre-Covid, and because of the distance to remote places in the audience (like where we were) there were monster screens showing the band.

The problem was, the visible playing on the stage was out of sync with what was on the screen - it looked really weird. Until I twigged what was happening.

The image from the screen goes at speed of light to the audience member (so pretty much instantaneous). But the sound took perhaps 0.3 seconds to arrive. So the video signal is delayed with respect to the sound by 0.3 seconds so that everything is back in sync. Anyone sufficiently close to the stage to not need the screens simply sees the band and the sound live.

I told this to my 36 year old son, a guy who has been to several big music festivals. He replied that it was obvious, and big venues have done that for quite a long time.

Craig
The delay is inherent in the video system rather than being inserted, all LED walls have some amount of processing delay. The only delay that is generally used at concerts is for the speakers themselves, used to align any speakers further back from the main set to stop echoing.
Look at most festivals and you will have the main hang of speakers at the stage and then delay towers further back.
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Old 18th Jun 2021, 8:53 am   #2362
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Default Re: The Audiophoolery Thread.

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Here's a couple of audiopool (audiophile?) phrases that have both confused and entertained me for years:

Great sense of timing
If that phrase confuses you, then you've obviously never tried to integrate a subwoofer with stand-mount loudspeakers!

I have done that, yes. But explain, please do.
Well, then you'll know that, unless you get the subwoofer positioning, frequency and phase adjustment spot on, there's every chance that the bass line will be playing along out of time with the rest of the track, thus ruining the timing. Some subwoofers are much worse than others when it comes to this (I'm thinking B&O Beolab 2 and anything made by REL here!) but the same effect can even be found in poorly designed multi-driver loudspeakers.

Oh, and before you all start setting light to your pitchforks and marching up my driveway, this is nothing to do with audiophilia. It's simple acoustics.
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Old 18th Jun 2021, 9:13 am   #2363
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Default Re: The Audiophoolery Thread.

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We were at an Eagles concert pre-Covid, and because of the distance to remote places in the audience (like where we were) there were monster screens showing the band.

The problem was, the visible playing on the stage was out of sync with what was on the screen - it looked really weird. Until I twigged what was happening.

The image from the screen goes at speed of light to the audience member (so pretty much instantaneous). But the sound took perhaps 0.3 seconds to arrive. So the video signal is delayed with respect to the sound by 0.3 seconds so that everything is back in sync. Anyone sufficiently close to the stage to not need the screens simply sees the band and the sound live.

I told this to my 36 year old son, a guy who has been to several big music festivals. He replied that it was obvious, and big venues have done that for quite a long time.

Craig
The delay is inherent in the video system rather than being inserted, all LED walls have some amount of processing delay. The only delay that is generally used at concerts is for the speakers themselves, used to align any speakers further back from the main set to stop echoing.
Look at most festivals and you will have the main hang of speakers at the stage and then delay towers further back.
The son in question is a major project manager for AV systems, including every AV system installed here https://www.samsung.com/uk/explore/k...ross/discover/ including a 6m x 4m 0.3mm pixel pitch curved screen. He knows as much as there is to know about video processing delay. So I tend to trust what he says about purposely delayed video are large concert venues.

Craig
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Old 19th Jun 2021, 10:46 am   #2364
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Yes, he said, exactly.
At this point he was probably so very much pleased that you'd understood what he was getting at.

Actually, you could do it. It's just that the guitarist would need one separate pedal for each chord/note he could play, and that he'd have to tap the right one just at the right time before he played. If the pedal also did the note itself, there would be less need for the guitar...
Maybe a somewhat passable result could be achieved using statistic prediction and psycho acoustics. It would certainly make for an interesting effect.

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Old 19th Jun 2021, 6:21 pm   #2365
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Default Re: The Audiophoolery Thread.

https://www.audioaficionado.org/showthread.php?t=48917

Why?



Even if you had enough money to put this in your living room, I doubt the owner could get a gold played, cryogenically treated 630A 3P+N+E plug and socket to power it; not to mention to look of horror at the monsterous plug and socket.
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Old 19th Jun 2021, 7:13 pm   #2366
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Default Re: The Audiophoolery Thread.

Why? Why indeed, it isn't even a valve amp!
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Old 19th Jun 2021, 7:51 pm   #2367
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Default Re: The Audiophoolery Thread.

SIX 20kW class-A amplifiers?

So somewhere between 120 and 250kW static heat dissipation?

A very large room is going to be a pizza oven, a large auditorium will bring it down to sauna levels. Perhaps the electricity bills will be reassuringly expensive?


On a milder note, I spotted this guy reviewing some ATC speakers. Some of what he says seems reasonable. But he has a thing about ferromagnetic materials in connectors or mere PVC insulation on wires. He'd almost earned a bit of credibility before that.

https://www.youtube.com/watch?v=irdIUAcA7MU

David
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Old 19th Jun 2021, 8:05 pm   #2368
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Default Re: The Audiophoolery Thread.

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a thing about ferromagnetic materials in connectors
Darn it, I have ferromagnetic stuff inside my 'speakers too, pity I sold my ESL57's, hang on, they had a couple of transformers in them. Must get some brass USB connectors for the audio transfer and (well off topic) pictures too, it must make them prettier!
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Old 19th Jun 2021, 9:53 pm   #2369
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Default Re: The Audiophoolery Thread.

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https://www.audioaficionado.org/showthread.php?t=48917

Why?



Even if you had enough money to put this in your living room, I doubt the owner could get a gold played, cryogenically treated 630A 3P+N+E plug and socket to power it; not to mention to look of horror at the monsterous plug and socket.
I've seen that amp posted elsewhere a few years ago. Perhaps it would have very slightly more credibility if the did not quote Watts RMS, which is a meaningless number.

Craig
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Old 20th Jun 2021, 1:03 am   #2370
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Default Re: The Audiophoolery Thread.

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Perhaps it would have very slightly more credibility if the did not quote Watts RMS, which is a meaningless number.

Craig
Why’s that, then?
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Old 20th Jun 2021, 6:14 am   #2371
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Default Re: The Audiophoolery Thread.

Root of mean square is an operator that only makes sense in terms of values which are dimensionally voltages or currents.

Take voltage samples (or current) and square them and you get a result proportional to power. Take the mean of these power samples and you get the mean power, of course!

Take the root of the mean power and you're back to voltage (or current) again. You now know the fixed DC voltage (or current) that would have the same average heating power as the AC+DC components of the original samples.

If I sampled the voltage coming out of a mains socket here, I'd get sam[les ranging from -339.4V to +339.4V, all being well. If I took them quickly, I could plot out a sinewave. If I took plenty of samples, many cycles of the sinewave, and took the average of them all, I'd get zero volts. This looks like an oddity. Stick a resistor across the mains and it gets warmer. The thermal mass averages the heating over many cycles and some calorimetry will tell me the average power being dissipated. So something with zero average voltage is producing non-zero average power. This ought to strike you as odd. But it's the way things work.

Voltage and current are alright, but it's the power that does the real work. Like the exhortation to people analysing crime to 'follow the money' in electrical, electronics and RF work, keep an eye on the power. You need to know it when you want to see signal to noise ratios.

Noise throws you another googlie.

Mean voltage of pure gaussian noise is zero. Peak voltage is +/- infinity.

So we put the noise through a properly impedance-matched 10dB attenuator. That must reduce the power tenfold, right? so voltages are reduced by root(10), which is a factor of 3.16228 etc. So infinity divided by 3.16228 is, oops! still infinity! If you look at peak voltage, there has been no decrease at all. The mean voltage is still zero, and the peaks are still infinite. The shape of the probability density function has narrowed, that's what.

So statisticians, engineers and the like need a tool to get a grip on the 'power' of a gaussian random signal that tells them something other than zeroes and infinities. So they picked the points on the Gaussian pdf where the probabilities are one-over-root-two of the peak probability of the bell-shaped curve. If these were voltage samples, then these would be the points where their 'power' was halved. The spacing between these points is called the "Standard Deviation" which is the usual way to talk about the amount of variance on some parameter. In electronics terms, the standard deviation is the same as the RMS value of the samples that make up the population, neglecting the DC component (if any). So the recipe for Standard deviation is to remove the mean (DC component) and take RMS of the remainders.

Think of an investment fund manager. He doesn't make money off of the absolute prices of the stocks he deals in, he makes money off of the fluctuations. If stock prices all stayed stationary, he'd starve.

So in terms of power, it makes sense to talk of average power or sustained power.

If you look at this in terms of voltage (or current) then this can be expressed as RMS volts into a defined impedance (or RMS amps, of course)

Talking of RMS of power, when what is actually meant is the mean power, is an indication that someone doesn't understand what they're saying, probably just mindlessly following others.

If I take an RMS voltage and square it, then divide by the resistance of the load, I get the mean power as my result.

If I have some power and I take its mean value, I multiply by the load resistance and then square root it, I get the RMS voltage as my result.

Mean is important in terms of power

RMS is the equivalent in terms of voltage or current.

David
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Old 20th Jun 2021, 7:20 am   #2372
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Default Re: The Audiophoolery Thread.

Another way of looking at this is to consider a simple case of a pulse waveform.

Suppose we have a DC level of zero volts for 90% of the time, and 1V for 10% of the time. Repeated infintely.

Connect this waveform into a 1 ohm resistor. What power is dissipated in the resistor?

Clearly it is zero watts for 90% of the time, and 1W for 10% of the time. So on average the power dissipation is 0.1W.

This generalizes to any waveform; the important factor is average (or mean) power.

Although you can generate the RMS value of the power quite straightforwardly mathematically, it is a meaningless number, and as David says.

Craig
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Old 20th Jun 2021, 4:40 pm   #2373
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Default Re: The Audiophoolery Thread.

I am not going to dispute the preceding arguments, BUT.
My understanding of RMS power, around and in general use for many decades, is as follows. A sine wave input to an amplifier comes out at a consistent amplified level (let us say 1v rms) and it is fed to a loudspeaker whose impedance is, say, 4 ohms. By taking an infinite number of samples of the voltage, squaring them, adding together then finding the square root, you have a mean voltage into the 4 ohms, yielding a mean power output.
Of course that must be a a fixed frequency, which must be at a frequency where the loudspeaker's impedance is the stated 4 ohms.
Certainly not correct for all frequencies that can pass the amplifier, and all the loudspeaker impedance presented at those different frequencies, but a comparison nonetheless.
It was a term happily used for all the stuff I looked at until about 30 years ago when it was *******ised into "music power" and then "Peak music power" and maybe others.
So putting aside the absolute mathematics of confusion, is it not a reasonable term to use?
Les, whose maths never really got beyond "O" level in spite of his 8 years at technical college.

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Old 20th Jun 2021, 4:46 pm   #2374
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Default Re: The Audiophoolery Thread.

Watts RMS is alas similar to measuring area in metres, or the height of a building in square yards.

Craig
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Old 20th Jun 2021, 4:56 pm   #2375
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Default Re: The Audiophoolery Thread.

It's a bit like seeing someone discussing 'square acres'
square yards, square miles, square metres are fine, but acres already include the squared measure bit.

You're perfectly right that the power calculations are all over the shop with the wandering impedance of a loudspeaker. But people want to see power numbers and they aren't aware of how misleading they can be. Still, it's no excuse for giving the power in wrong units.

The amplifier in my lounge can swing +/-50V and +/-15A... whatever power that means depends on the speaker, also, it depends on the waveshape.

Somewhat dodgy firms exploited all the lack of understanding and we got many forms of peak power IHF etc. This dodgy spec inflation reached its high point in the 'CB burner' amplifiers coming out of Italy in the eighties

David.

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Old 20th Jun 2021, 5:22 pm   #2376
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Default Re: The Audiophoolery Thread.

Surely a square acre would be a volume, 9 million cubic feet ish.
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Old 20th Jun 2021, 6:21 pm   #2377
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Default Re: The Audiophoolery Thread.

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Watts RMS is alas similar to measuring area in metres, or the height of a building in square yards.
Are we sure about this ? If we square a quantity, then operate on it in such a way as not to change its dimension (as in taking a mean of a distribution), then take the square root again, we'll end up with something which has the same dimension that we started with. So the dimension of 'watts RMS' will still be watts, which is correct for measuring power. It might not have any helpful meaning (see posts above) but it won't actually be dimensionally incorrect.

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It's a bit like seeing someone discussing 'square acres'
square yards, square miles, square metres are fine, but acres already include the squared measure bit ...
Yes, trying to read any meaning into the squared bit would be difficult. But once we've 'rooted' it back to acres then, well, that's clearly just an area again and we can open our eyes and breathe out .

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Surely a square acre would be a volume, 9 million cubic feet ish.
A volume has three space-like dimensions, but a square acre would need four. In our everyday world we don't think of there being more than three space-like dimensions, but it has been theorised that there might be e.g. here https://phys.org/news/2014-12-universe-dimensions.html.

I once went to a very good talk by Steven Weinberg (Nobel prize winner) who tried to illustrate how the dimensions beyond three might be 'compactified' so small that we can't ordinarily perceive them. He held up a drinking straw and said that the people at the back of the lecture theatre would perceive this as a one-dimensional object. If you asked them where a dot on the straw was they'd just tell you how far along the straw it was. But if you asked an ant, who was walking on the straw, then it would tell you both how far along and how far around the straw the dot was, because on a small enough scale (an ant scale) it was clear that the straw was a surface, with two dimensions, not just a line with one.

Cheers,

GJ
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Old 20th Jun 2021, 6:26 pm   #2378
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Default Re: The Audiophoolery Thread.

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but a square acre would need four
Ah I missed that, still 9 million cubic feet and an added (possibly time) dimension or nice fluffy edges. Or use acre to the power of root two (grin). And I do agree a bit that watts RMS is a silly thing to do but doesn't change the value and can be a clarifying feature of a specification for the layman. Waiting for gun fire...
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Old 20th Jun 2021, 8:17 pm   #2379
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Default Re: The Audiophoolery Thread.

I've kept out of this for a while. But I hope I understand the principle under discussion now. When I first came to working with audio systems my Boss at the time had the same problem with Watts RMS but I agree with his, and people who have said the same here's point. You can have RMS volts or RMS amps. But since power is related to either volts or amps squared then a root mean of the square is like a double negative in a way.
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Old 20th Jun 2021, 9:09 pm   #2380
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Default Re: The Audiophoolery Thread.

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And I do agree a bit that watts RMS is a silly thing to do but doesn't change the value and can be a clarifying feature of a specification for the layman.
Would not the “RMS power” number be different to the “average power” number for a given situation?

For a sine wave voltage driving a resistive load, the resultant power curve is a sine wave of twice the frequency, displaced in the positive direction so that whilst it periodically touches zero, it never goes negative. Let’s say for a specific example the curve oscillates between zero and 10 watts, for an average of 5 watts. But the points on the curve above 5 watts have a bigger effect on the RMS value than those below 5 watts. One may do a very rough approximation using just the (nine) pi/4 points of a cycle, namely 5, 8.5, 10, 8.5, 5, 2.5, 0, 2.5, 5 watts. The sum of the squares is 332, the mean of that is 36.89, and its square root is 6.07. That indicates that the RMS power number will be a little larger than the average power number.

One could say that amplifier makers who quote RMS power but use the average power number are in fact missing an opportunity to inflate their published power outputs.


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