Hacker News Board Hacker News, browsed like a classic message board
Live data from Hacker News

Installing VLC Media Player voids your speaker warranty

en.community.dell.com

Post reply on HN
Print view View original

181–190 of 224 posts

Re: Installing VLC Media Player voids your speaker warranty

#181

Post by marshray »

tmoertel wrote: post #153
lutusp wrote: post #152

Earlier quoted context omitted.

> I don't know of any widely used definition of "clipping", But there is one. In electrical engineering, it's any process that arbitrarily limits a signal's amplitude. By far the most common meaning is a signal that exceeds the voltage range of an amplifier or signal pathway. > nor any definition that fits the context of this discussion, that allows for a signal's peak value not to be reduced. See above. > It's calle…

We must be talking past one another. I thought I was speaking in the electrical-engineering sense of clipping (my undergrad studies were in EE). In any case, to make sure we're talking about the same things, I'll be more formal. Let y ( t ) by a time varying signal. Now define a maximum amplitude V > 0. Let us say that clipping occurs at time t if | y ( t )| > | V |. Define the clipped version of y to be w ( t ) = ma…

Consider it in the frequency domain: clipping adds odd harmonics.

The fundamental frequency is reduced in energy a little bit, but the higher frequency harmonics end up containing relatively large amounts of energy.

Re: Installing VLC Media Player voids your speaker warranty

#182

Post by lutusp »

tmoertel wrote: post #153
lutusp wrote: post #152

Earlier quoted context omitted.

> I don't know of any widely used definition of "clipping", But there is one. In electrical engineering, it's any process that arbitrarily limits a signal's amplitude. By far the most common meaning is a signal that exceeds the voltage range of an amplifier or signal pathway. > nor any definition that fits the context of this discussion, that allows for a signal's peak value not to be reduced. See above. > It's calle…

We must be talking past one another. I thought I was speaking in the electrical-engineering sense of clipping (my undergrad studies were in EE). In any case, to make sure we're talking about the same things, I'll be more formal. Let y ( t ) by a time varying signal. Now define a maximum amplitude V > 0. Let us say that clipping occurs at time t if | y ( t )| > | V |. Define the clipped version of y to be w ( t ) = ma…

Here's the first crossroad, where we diverge:

> Now define a maximum amplitude V > 0.

The problem being discussed is one in which the user cranks up the volume such that the maximum volume level is far exceeded, and the amplifier circuit, which cannot reproduce the higher level, instead clips the waveform at the supply voltage.

> The claim you made that sparked this conversation was this: "the resulting clipped waveform carries a lot more energy than an unclipped one."

And it does, as you can see from this diagram:

http://i.imgur.com/oE5NFZ9.png

The red trace is the 100% volume level for the system, and it is not clipped. The green, "clipped" trace is far above 100%. It's really very simple.

> But this claim seems to contradict my Claim 2.

Yes. Your claim 2 doesn't apply to a case in which the maximum output voltage of the amplifier cannot reproduce the input waveform. So instead the amplifier clips its input signal at its voltage limits, as the above diagram shows.

The interesting thing about this analysis is that two ways to analyze it produce the same result.

If we use a simple integration of the unclipped and clipped cases, we see a power increase of 2.46, as discussed earlier.

If instead we use Fourier analysis to examine the harmonics of a sine wave and a square wave, the square wave's higher harmonic energies sum to 2.46 of the original sine wave's energy level in the speaker (but pi/2 above the sinewave voltage levels):

Sine wave harmonic lines = 1f

Square wave harmonic lines = (4/pi) sum(sin(2 pi f t (2k-1) / (2k-1),k,1,oo) (http://en.wikipedia.org/wiki/Square_wave#Examining_the_squar...)

The outcomes obviously have to come out the same. The above shows how they do it.

Re: Installing VLC Media Player voids your speaker warranty

#183

Post by dpe82 »

mikeash wrote: post #176
dpe82 wrote: post #173

Earlier quoted context omitted.

It's more complex than that. Let me explain: Audio is typically passed into a soundcard's digital audio converter (DAC) as integers representing samples of the audio waveform. For example, a full volume sine wave looks something like this[0]. That signal is perfectly safe to play on any hardware. However, if you take that same sine wave and increase the amplitude you end up with values outside the valid range so you…

Thanks for the info. I was familiar with most of that, but didn't think the difference would be so big. How much of a "safety factor" are we talking about between the ability to handle normal audio and the ability to handle this sort of catastrophic case? In other words, how much would you have to turn down the maximum volume limit? Is it a factor of 2, or 10, or 100...? If it's a factor of 2, for example, just take…

It's hard to know. Speakers are insanely complex beasts whose electrical reactance changes depending on the signal. To simplify things we use measures like RMS current ratings for amplifiers because if you put a sine wave through a speaker they tend to approximate a resistive load due to most of the load being air, and we use nominal impedance to describe speakers because while even though for something as simple as a sine wave a speaker's impedance can vary 4x from nominal depending on frequency, it at least gives us something we can reliably measure.

Once the signal is more complex than a sine wave things get crazy. The more frequencies in a signal, the harder it is to model the power draw since different parts of a complex curve cause the speaker to act more like the low resistance inductor it actually is. Discontinuities and areas of constant voltage (both caused by clipping) are the worst, and to make things even more fun the amplifier is part of the system and affects things as well.

But assuming you know a lot about the speaker, the amplifier and the DAC you could probably build a model that works well for simple sinusoidal audio, but that doesn't cause problems anyway. All bets are off for anything more complex.

So instead you're left with a few options: buy reasonable gear and don't play crap audio, play crap audio but massively overbuild your system so you lower the risk of getting into the unknowable danger zone that changes depending on what you're playing, or use a bunch of heuristics on a signal and try to distort it in some way so it's less potentially damaging.

The problem with the latter is since you don't know where the line is it's easy to be overzealous and end up distorting lots of stuff you don't need to. Problem with the middle is you either end up with something much larger and more expensive than you need, or you cripple what you have to give you a wider margin of safety. Problem with the first is apps like VLC make it exceptionally easy to accidentally play crap audio. Pick your poison.

Could Dell spend a couple extra bucks for higher quality components and create a wider margin of safety? Probably yes. But at the same time the VLC developers are being reckless by putting a tool into consumers hands that makes it so easy to play potentially damaging audio signals.

Edit: clarifications

Re: Installing VLC Media Player voids your speaker warranty

#184

Post by lutusp »

mikeash wrote: post #176
dpe82 wrote: post #173

Earlier quoted context omitted.

It's more complex than that. Let me explain: Audio is typically passed into a soundcard's digital audio converter (DAC) as integers representing samples of the audio waveform. For example, a full volume sine wave looks something like this[0]. That signal is perfectly safe to play on any hardware. However, if you take that same sine wave and increase the amplitude you end up with values outside the valid range so you…

Thanks for the info. I was familiar with most of that, but didn't think the difference would be so big. How much of a "safety factor" are we talking about between the ability to handle normal audio and the ability to handle this sort of catastrophic case? In other words, how much would you have to turn down the maximum volume limit? Is it a factor of 2, or 10, or 100...? If it's a factor of 2, for example, just take…

Remember that each technical measure you add to a design represents another (a) cost (b) size/weight, and (c) possible failure mode.

> When the running average surpasses a value that indicates the speaker is reaching its limit, cut the volume. I take it that this doesn't work?

No, it might work, but it's really a question of cost, complexity and represents an added failure mode -- something else that can go wrong.

Re: Installing VLC Media Player voids your speaker warranty

#185

Post by 72deluxe »

malandrew wrote: post #99
astral303 wrote: post #74

Earlier quoted context omitted.

A square wave has twice the power of a sine wave of identical amplitude. This is why distorting the amplifiers (especially digital clipping) is so much worse for speakers than overpowering the speakers. This is a very well known fact in audio circles. Playing metal at full volume is not as damaging as playing anything intensely digitally clipped at full volume. Yes, Dell is putting on shitty speakers on their laptops…

Most metal released these days is digitally clipped. Even classic old 80s "remastered" records are digitally clipping all over the place. The loudness wars has ruined most metal through remasters.

Ah yes, the death of dynamics in music! One horrendous offender that I own is Paul McCartney's Memory Almost Full. I think he remastered it and rereleased it but there isn't a chance that I'm spending my money on it again! I think the mastering engineer discovered the joys of gain and hard knee in compressors.

Re: Installing VLC Media Player voids your speaker warranty

#186

Post by xerophtye »

jbk wrote: post #25
speeder wrote: post #23

Earlier quoted context omitted.

Any other manufacturer do that? (someone mentioned HP below) I am a VLC fan (thanks! I wish I was skilled enough to contribute to the project) and right now using a ASUS laptop, I want to know what manufacturers I should NOT buy from next time (I bought this ASUS because I tried to buy from DELL and their site was buggy and did not closed the transaction... good to me their site was buggy!)

> Any other manufacturer do that? We heard about HP and Dell doing that, and ONLY in the version they shipped to India or South-East Asia (Do they ship worse components there?) > I wish I was skilled enough to contribute to the project There is a very high chance that you are skilled enough, to be honest.

> (Do they ship worse components there?)

There is actually a chance that they might be, considering not all models are available in all regions, thus there are models that are marked for South-East Asia. So as a manufacturer, it's relatively easy for them to be biased.

That said, vendors in South-East Asia have a history of being scammers and taking out original parts and replacing them with cheaper hardware, so that could be a cause too, and HP might be innocent.

Re: Installing VLC Media Player voids your speaker warranty

#188

Post by mikeash »

dpe82 wrote: post #183
mikeash wrote: post #176

Earlier quoted context omitted.

Thanks for the info. I was familiar with most of that, but didn't think the difference would be so big. How much of a "safety factor" are we talking about between the ability to handle normal audio and the ability to handle this sort of catastrophic case? In other words, how much would you have to turn down the maximum volume limit? Is it a factor of 2, or 10, or 100...? If it's a factor of 2, for example, just take…

It's hard to know. Speakers are insanely complex beasts whose electrical reactance changes depending on the signal. To simplify things we use measures like RMS current ratings for amplifiers because if you put a sine wave through a speaker they tend to approximate a resistive load due to most of the load being air, and we use nominal impedance to describe speakers because while even though for something as simple as…

I don't really get this description of mitigations as "overzealous". Sure, there's going to be some margin there, but that's just good engineering. The rev limiter on my car's engine doesn't kick in right at the critical RPM where everything falls apart, but some amount below. My CPU's thermal underclocking doesn't start right at the temperature where the component fails, but some comfortable distance below. You could argue that both of those are "overzealous" protections that cause me to lose out on performance I could potentially have otherwise, and that's true, but good engineering in this case generally means using a safety factor for these things.

I don't understand how you can blame VLC at all. Technically, Dell shipped a tool right on the machine that makes it just as easy to play potentially damaging audio signals. Internet Explorer could just as easily play a WAV file that's been crafted to destroy the computer's speakers. The correct approach is to remove that ability, not blame a tool that accidentally triggers the problem.

Re: Installing VLC Media Player voids your speaker warranty

#189

Post by mikeash »

lutusp wrote: post #184
mikeash wrote: post #176

Earlier quoted context omitted.

Thanks for the info. I was familiar with most of that, but didn't think the difference would be so big. How much of a "safety factor" are we talking about between the ability to handle normal audio and the ability to handle this sort of catastrophic case? In other words, how much would you have to turn down the maximum volume limit? Is it a factor of 2, or 10, or 100...? If it's a factor of 2, for example, just take…

Remember that each technical measure you add to a design represents another (a) cost (b) size/weight, and (c) possible failure mode. > When the running average surpasses a value that indicates the speaker is reaching its limit, cut the volume. I take it that this doesn't work? No, it might work, but it's really a question of cost, complexity and represents an added failure mode -- something else that can go wrong.

In my opinion, it should be impossible to physically damage a computer from user-space code. I'm surprised that this seems to be such a controversial opinion.

Given that, a computer which allows random audio API clients to destroy the computer's speakers is not correctly designed. Certainly, it may add cost, size, and weight, but if that's what you need for correctness, then that's what you need for correctness.

The brakes on a car add cost, size, and weight, but you can't just leave them out because you don't feel like accepting that penalty.

Re: Installing VLC Media Player voids your speaker warranty

#190

Post by ferongr »

jjoonathan wrote: post #170
ferongr wrote: post #129

Earlier quoted context omitted.

While any software that accesses an audio interface using integer formats, VLC is to my knowledge the only average user-oriented program that can end up in such situations. I would suggest VLC disables this feature for new installs and move it to an easily discoverable preference. Or if they really care enough to allow their users to boost the volume levels of quiet movies to replace the gain multiplication with a pr…

> VLC is to my knowledge the only average user-oriented program that can end up in such situations Windows Media Player, Firefox, iTunes, ... VLC makes it easier (you can boost a quiet song or movie until it fills the OS-defined dynamic range) but a loud song in any other piece of music playing software would have the same effect. Depending on the genres of music you listen to, it's not uncommon to come across songs…

>Windows Media Player, Firefox, iTunes, ...

None of these drive the signal to digital clipping.

Post reply on HN