Axiom Home Page Forums General Discussion The Water Cooler all AMP'S sound the same

Hey wait a minute -- inquiring minds want to know! I'm assuming the difference would be audible in the region between 15K and 20K, with more transparency and less stridency in something like a naked recording of a ride cymbal.

But then, I haven't done the test...

OK, the reason I could tell the difference so easily, as is the case in so many experiments, I had a flawed assumption, and mis-prepaired the samples, so what I thought I was testing I was not, but instead testing something else entirely.

I've had the discussion about sampling rates numerous times, and had even done the math to show what I believed to be correct. But as I said above, what I believed was not what the Nyquist Sampling Theorem actually says.

I always heard talk of the Nyquist limit, that being half of the sampling rate. That's not the whole picture. In my own calculations I saw trouble if a signal was right at the half-way point (like encoding a 24kHz sine wave at 48kHz), or if there was any harmonic content above the limit.

Turns out Nyquist had already accounted for these cases, and specifically excludes them from the theory. From Wikipedia, "the theorem shows that a bandlimited analog signal can be perfectly reconstructed from an infinite sequence of samples if the sampling rate exceeds 2B samples per second, where B is the highest frequency of the original signal." There's a lot of information in that little blurb. One, the sampling rate must exceed twice the highest frequency. So the 24kHz wave can't be perfectly reconstructed if you sample it 48,000 times a second, it must exceed 48k. The other, the signal must be bandlimited. That means the signal must contain no content at or above half the sampling rate.

So my test of a saw wave at 10k, was not valid. I picked that waveform because of it's harmonic content so there'd be something to hear in the upper octaves. It contains both even and odd harmonics. But that means the 10k fundamental had considerable content at 20k, 30k, 40k, and beyond. The first odd harmonic (30k) had already exceeded the limits of what the Sampling Theorem stipulated.

What happens when you have content beyond the Nyquist limit when sampling, is you get strange aliasing artifacts. It's a 1D interference pattern, you get peaks where they shouldn't be. Choose a different sampling rate and you get a completely different pattern of bad data, but it all sounds similar enough to saw-tooth harmonics that if you were to play only one sample it'd seem reasonable enough that what you were hearing was right. But when you sample exactly the same data at a different rate and get you get different harmonic content. It's obvious something is wrong.

So yeah, my ABX trial was fine, the data I was testing was produced by a incorrect premise. I'm trying to come up with a valid trial, but I need a lot of harmonic content to be audible, but can't have any of it reach or exceed 24kHz.

Chris, I really think that your calling is as a professor. You have such talent for explaining complex matters in understandable ways. I really enjoy and appreciate learning from you!

I just want to see Chris driving around in his car playing dubstep while wearing tweed.

I bought my newest 2 channel amp because i wanted an amp with an almost unlimited amount of power... The amp that i got has WAY more power than i would ever need. It is also one heck of a piece of engineering, the build quality is amazing, the exterior is built of all machined aluminum, and looks like the beast that it is.

The (Bose) stereo in my car is broken. But I should totally get a tweet driving cap, then I can hum the dubstep.

In my house are many rooms, if it were not so, I would not be able to prepare places for so many amplifiers.

I can tell you, not all solid state amps sound the same. Not even close and the differences are obvious to a discerning listener.

However, if one believes as an a priori that all "well designed" (please feel free to drive your Kenworth through that one) solid state amplifiers sound the same, then all distinctions will end up like the toes of Cinderella's sisters, so the foot might better fit.

2x6, remember that rooms are the second most sound-altering component (right behind speakers) of the entire system. You have many amps in different rooms, correct?

Now, I'm sure over the years you've swapped out different amps in the same room. Of these times, how often were you able to switch amps quickly -- as close to instantaneously as humanly possible? How many of these times did you ensure that levels were matched as closely as possible when you compared?

A fundamental principle of human sensory processing as that our senses have a poor memory. The brain does not store raw data. You can't re-access your unbiased impression. Once it's in memory, it's linked with emotion and bias -- e.g. "Whoah, that sounded crisp, clear, and wide open! I'm pretty sure I like it more than the other amp" is something your brain would file away for later retrieval.

So, how do we get around this limitation? Instantaneous, level-matched swapping! Even when done in a non-blind situation, it's a much more reliable method of discerning differences between devices (speakers, amps, media players, etc.). Of course, as all of us in the "brain trust" have tried to convince you of before, the only way you can definitively say that one sounds better than the other is to remove as much unwanted bias as possible. Unwanted bias comes from your eyes. It comes from knowing the price and build quality. It comes from everywhere but the actual audio you hear.

Which product sounds better to you is the only bias that matters. And, as has been shown time and time again, when tested in a rigorous scientific way, the theory that well-designed amps sound the same has not been contradicted. For this reason, it's as believable as the theory of gravity.

The methodology is living with a component in a system over a period of time. Some systems 'shine,' some are competent, none are less than that.

As to Cam's moronic tag that "socialism is the essence of love," The problem with socialism is that some ruling elite decides which class is to be a privileged class of takers and which to be givers. I don't think it is fair that I should work and pay for the food, shelter and medical care of someone who sits on his ass, smokes crack, and sleeps all day. I don't think it is fair that someone should vote how much of my income should be confiscated by taxation and given to another as a reward for their indolence.

Socialism is not love. It is theft from the productive and a reward for the indolent.

As to those who are unable to care for themselves, because of injury or illness, then society should care for them.