Is there a real benefit to preamps or two channel amps in HT? - Page 4 - Home Theater Forum and Systems -

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post #31 of 33 Old 04-27-08, 07:32 PM
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Re: Is there a real benefit to preamps or two channel amps in HT?

Wayne A. Pflughaupt wrote: View Post

Assuming Rod Elliot was referring to equalization, we get a contrasting (conflicting?) view from Rane’s Exposing Equalizer Mythology by Dennis Bohn (bold emphasis added):
“Phase shift is not a bad word. It is the glue at the heart of what we do, holding everything together. That it has become a maligned term is most unfortunate. This belief stands in the way of people really understanding the requirements for room equalization.

Associated with each change in amplitude is a corresponding change in phase response. Describing them as unbelievably jagged is being conservative. Every time the amplitude changes so does the phase shift. In fact, it can be argued that phase shift is the stuff that causes amplitude changes. Amplitude, phase and time are all inextricably mixed by the physics of sound. One does not exist without the others.
I think what Mr. Elliot failed to consider is that equalizers also introduce phase changes, which probably accounts for how it’s usually possible to EQ phase-related response problems around a sub’s crossover region.

Overall though, that was a very good article. Thanks for linking it. I especially liked the part about mics not "hearing" the way our ears do. That's probably why you don't get much of an audible improvement equalizing subs beyond smoothing out the worst problems. I.e., piling on lots of "minutiae" filters smoothing out every little ripple in response you probably won't be able to hear the difference with them in or out. I sure can't.

You are correct, but I belive Mr. Elliot was thinking on a slightly different line. Of course when dealing with EQ's amplitude and phase are related(with the exception of a linear phase EQ). In the real world(no EQ) they are not so incontrovertably linked. You can have the identical phase of two signals with two completely, even opposite amplitudes. Also the time which Mr. Elliot and yourself are referring to are on different scales. a 10 degree phase shift at 80 Hz (wavelenghth of 4.2m) takes a little over a 1000th of a second. Room nodes can cause differences in time of an 80Hz note of a second or more. So an EQ(even a very poor "phasey" EQ) can come nowhere close to adjusting that kind of time.

PS. Someone please correct me if my math is wrong, it's been quite some time since I've had to work out any formulas.
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post #32 of 33 Old 04-28-08, 06:52 AM
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Re: Is there a real benefit to preamps or two channel amps in HT?

DS-21 wrote: View Post
I don't doubt any of that. However, "that sound" as you put it is by definition a coloration, a deviation from sonic accuracy. I'm proceeding from the assumption of someone interested in recapturing what someone like you originally put on the disk/file, which is that the sound one wants from one's electronics is no sound at all. Such sonic transparency is by and large attainable today for very, very little capital outlay in electronics, because most gear from the middle-low-end to the middle-high-end is designed for that end. At the blue light special end, one's more likely to see nonflat FR, e.g. the Sonic Impact T-amp, which sounds so much like a SET because it has no power and significant rolloffs at the frequency extremes. Likewise, much of the stuff at the tippy-top of the "high end" is not so much "designed" as "haphazardly thrown together on a kitchen table," though there are certainly exceptions in the bleeding price sphere (Meridian, Lexicon, TacT, etc.).
Colouration is not always the goal. Often pure transparency is required in a piece of gear. Particularly amplifiers. True transparency can be just as expensive as boutique "flavoured" gear. Now it's possible that manufacturers can use cheap IC components to create pure sonic transparency for just a few dollars, but if they can, there must be a huge conspiracy amongst all the manufacturers to gouge us end users, by not releasing these cheap transparent pieces of equipment. Ockham's Razor would disagree, but this certainly doesn't mean that it's impossible.

DS-21 wrote: View Post
With that caveat in place, I agree that we're more-or-less in agreement.

The only difference then, perhaps, is whether a corresponding measurable difference falls within the range of audibility. I don't think that just because there's a measurable difference there will be an audible difference. Take THD, which is by-and-large a meaningless number anyway. A difference between 0.0001% and 1% THD may not be at all audible, depending on where it falls. If it's 2nd order distortion, then it probably won't be. If the distortion spectrum is a high odd order, then it is far more likely to be audibly different. That's not to say that higher measured accuracy isn't ipso facto "better," but only that when one thinks of an audio system in its totality for someone with limited resources, the wise and rational course is to spend as little on things of no to debatably marginal audible difference, and transfer the money that would otherwise be squandered on commodity boxes into superior speakers and
Absolutely, not all measurement differences are audible. Also all audible differences are somehow measurable. However what is audible to some might not be audible to others. I'm not talking about these "golden ears" who supposedly have hearing like dogs. It has more to do with training. For example, my hearing is very good(tested annually by an audiologist), however I am still learning to hear things that I have never heard before. Depth for example can be something difficult to quantify. Particularly with a mono source. However a much more experienced engineer and I did an ABX shootout with some microphones, and he showed me how with certain mics depth can be achieved with a mono source. I couldn't hear what he was talking about at first, until he started to describe it to me, and then bam! I could hear what he was talking about. After that, I could hear this every time, and even compare this new variable between other mics. This is not a function of the human ear but of the brain. I became aware of what my ear was hearing all along, making it a reality for me. My hearing will continue to deteriorate as I grow older, and will never be as good as it is today.(without vast increases in medical science) However my listening improves every day.

DS-21 wrote: View Post
I use the shorthand "broken" to cover "components with audible differences due to measured failings in one or more areas that cross established thresholds of audibility." Why? Because it's either broken in that something's physically working wrong, or "broken" in that the design process intentionally led to something deviating from sonic transparency.
With this in mind I consider from the point of sonic transparency that there are a great deal of "broken" audio equipment out there. I would even say the majority.

DS-21 wrote: View Post
Here we disagree. I've done DBT's (can't call them full ABX because switching was manual rather than the superior method with a comparator box) that found tube amps (Sonic Frontiers) to sound the same as transistor amps (Classe, so by extension Adcom given that the Classe and Adcom amps sounded the same), and DBT's that showed rather unique chip amps (the TI PurePath DAC+amp stage in the Panasonic XR55 receiver) to sound the same as traditional bipolar chip amps. So I think that all of the currently available technologies can lead to sonic transparency if that was the design goal to begin with. Admittedly, for some of the stuff (mostly at the very high end) that is not necessarily the goal.

Now, I agree that badly designed tube gear is going to sound different. Not to say that someone may well prefer the colored sound. But sometimes it's just plain badly design, such as a conrad johnson preamp I once auditioned that had a massive channel imbalance. And no balance control, of course.
It is very difficult to do DB ABX tests with amplifiers. It requires a very complex testing system. One thing to consider. Even the absolute best tube designs are not completely linear, depending on signal level. So if you ran a hotter or quieter signal your findings could have been different. Also I would be shocked to find a tube amp and an IC amp that measure identically. Those measurement differences are there to be sure. So I guess what we're arguing is whether these differences are audible or not. Something one can really only decide for oneself.

DS-21 wrote: View Post
Quite the contrary. A sonically transparent piece of gear will faithfully transmit all of the colorations that the recording artist intended to be in there. It won't add more.
True. I am just hypothesizing that your DSP adding EQ to final signal is colouring the original signal, despite what the gear might be reproducing.

DS-21 wrote: View Post
Depends on the kind of purist. If one's trying to reproduce the perfect cup of coffee (for me, a melange from Cafe Havelka on Dorotheregasse in Vienna, which is what Gustav Mahler drank, kaffeekultur being of course an Austrian innovation that the Italians were more adept at marketing to the world), then one will of course add milk.
I was just trying to use he analogy to make a point. Not enough up on coffee history to keep up with you. I'm perfectly happy with Haitian Blue, 1 cream 1 sugar.
post #33 of 33 Old 04-28-08, 05:51 PM
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Re: Is there a real benefit to preamps or two channel amps in HT?


Since the discussion was getting seriously sidetracked with the DSP / time domain EQ issue, we’ve moved that part of the discussion over to the Waterfalls thread on the REW Forum. That required editing some of your posts to keep both discussions intact, so hopefully I have accomplished that without mangling your posts too bad. Anyone still interested in commenting on the DSP / EQ thing, please post on the other thread.

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