W A R N I N G !

W A R N I N G !

This page is full of non-facts and bullsh!t, (just like the internet and especially forums and other blogs), please do not believe entirely without exercising your intellect. Any resemblance to real things in reality is purely coincidental. You are free to interpret/misinterpret the content however you like, most likely for entertainment, but in no case is the text written on this blog the absolute truth. The blog owner and Blogger are not responsible for any misunderstanding of ASCII characters as facts. *cough* As I was saying, you are free to interpret however you like. *cough*

Thursday, November 27, 2008

It's clipping time

I already know my NeoMini DAC (strangely) clips when connected to the television. While cygig did mention that the NeoMini clips when driving his Triple-Fi, I never expected it to clip when driving a receiver.

And so I totally agree with his conclusion in his review of the NeoMini, because no matter how good the sound may be, if it clips it's gotta be a bad sound.

And that's what I'm experiencing with my new test set-up: Zhaolu D3, OPA627 op-amp with the following output stage bypassed, connected to Alessandro MS-1.

It clips obviously when volume is near the max. Even with the volume reduced to less than half, although it sounds much better, there are still traces of it clipping when the movement gets tough.

So that's what clipping (a bit of) sounds like. So that's what's been contributing to the noise in my Zhaolu D3, NeoMini, PSP, soundcard etc. So that's what's making the Cowon D2 sound so good. It's all about voltage and current swing. More correctly it's voltage swing and transient current supply, but they're related.

Lets see what happens in a few paint jobs:This is a wave, yea you know it.This is what happens with slew rate (voltage swing) is not enough, with the original wave in black and the alterations in blue.

On a square wave, it would make it look like a trapezium. Somebody once told me that it makes a sine wave look more like sawtooth, which suggests a faster drop than a rise, else it would look like a triangle if both are equal. But I'm no engineer and don't know how op-amps perform in real-life situations and the explanation for that.

How about some problem with current this time -It clips. Yes, insufficient current output causes clipping. This is because while the amp increases the voltage, it also increases current drawn by the circuit (V=RI), and when the current supplied cannot keep up, it causes a voltage drop, like in an unregulated or underpowered power supply, until the voltage drops to the point where the current can keep up. Which means the voltage cannot increase past that when the maximum current is reached.

While I know some people would not be able to understand this right away, it's basics to the pros. Right yan?Although in real life it'd be a bit like this, with rounded edges. There's no exact in everything, especially when it comes to electrical specs and overdriving. The above picture shows soft-clipping when it the corners are rounded, but depending on how much voltage swing or how early it clips, you'll still get a pretty hard clip most of the time when it happens. Or actually, when you actually notice the clipping it's a pretty hard clip already; soft-clipping gets passed off as distortion. I'm not confident enough to say what exactly it sounds like, maybe next time after I decide to hear more of it.

BTW the soft-clipping function on some amps/AVRs make the soft-clipping happens early when a certain voltage is reached so that it can round the corners more.

So if an amp cannot handle enough current or voltage swing (when the volume is too high), get another amp to do it. So now I totally understand the use of a preamp, other than to change the sound.

And now I totally understand the use of a second op-amp stage in the Zhaolu too (as well as many high-end products). Because the OPA627 alone feels a little grainy and not enough bass punch when connected to the Yulong. And connected to the MS-1, the above flaws are greater.

But still, it sounds much nicer than with the LT1028 or the JRC4556 pre-amp.

One thing still puzzles me though - why are clipping problems happening with the NeoMini when driving a receiver in a TV instead of headphones? And why is it happening to the OPA627 too when driving the Yulong? Aren't receivers supposed to have high resistance along the path?

Or perhaps, even with these good figures, one still cannot get the best sound. Audio is scary.

Really, one cannot base his beliefs on his limited knowledge. Because the real thing is different from whatever "facts" that he might know. Now that this kind of thing has happened to me I'll believe more in the EXPLAINABLE audio stuff. I'll still not believe that putting extra caps along the signal path will "improve" the sound, because it's explanable that it CHANGES the sound, but not IMPROVE, and definitely not make the source into any higher-current one.

BTW I might as well talk about the myth of speakers being killed by clipping, since I now have a picture that shows clipping and the original waveform.

The explanation is that clipping kills speaker by providing too much "DC" current, thereby transforming the speaker from a reactive load into a resistive load, heating up the coils and killing the speaker in the process.

But if you look at the graph, you can tell that the one-direction current over time is actually smaller.

Basically, even when there's clipping, the voltage still fluctuates between positive and negative, so the AC (as well as its frequency) is still the same.

What about the reactive load explanation, that energy is returned to the source in AC? If you look at where the clipping takes place, the green line shows the DC component while the black line shows the AC part. Yea, the AC is returned to the source, but the DC part is still the same.

Logically speaking, the amp isn't powerful enough to magnetize the coil properly, let alone kill it.

BTW I've had my Zhaolu clip TOTALLY before, hence it shows that clipping does not kill, if the power isn't great enough. But if the power IS great enough, it's the power that kills anyway.

So under what kind of situation will clipping really kill speakers? (I think most of the time it's the amp that die first isn't it? And in the process take-out the speakers too.) The DC reasoning is acceptable to me, but I'll need to find a way to generate a long enough DC current to kill. It's known that pure tones of 10Hz can damage your speakers, so it supports the above reasoning and shows that it's possible.

Now, how about if we add slew rate into the picture? This is just a noob guess but please bear with me, I'm sure it would be interesting even if it's wrong.

Imagine a wave that's clipping. It needs to go down to the negative voltage but somehow the slew rate isn't fast enough so the voltage is still positive when the next rise occurs. So the DC is there for an ultimately long duration. The voice coil heats up and "boom".

However, in order to do that, your DC component still has to be relatively great. I know my subwoofer has a DC offset because when I switch on the power, the cone gets sucked in and it starts whining. But it isn't dead yet, so I can safely say that before the DC component gets high enough to kill your ears are killed first, because the sound is going to be f-king distorted.

What about those YouTube videos of people blowing up their speakers by connecting 5V or 12V to them? Do the maths, to a 4 ohm driver, applying 5V is V^2/R = 5^2/4 = 6W. With 12V it's 36W. 6W will kill over time, but imagine your CPU or gfx card's 36W, without a heatsink, in a sealed container. I cannot think of anything that would't blow up. BTW 6W in AC is already very loud, that's the maximum low-distortion volume of a Tripath TA2024 T-Amp. As well as many PC speakers at full-blast without clipping (full-blast meaning with a loud enough input source).

So DC kills. But power kills also.

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