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Old 2nd September 2004, 03:40 AM   #1
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Default 3D Amp Reproduction?

I just attend a local "Hearing Session", to compare some commercial power amps. Some of the people there claims theirself to be "Audiophile"(but with no electronic understanding)

I found an interesting thing. Some amp have what they say "3D sound reproduction". The singer is sitting in front, while the music is in far background, it can be heared with closed eyes. The drums are in far left, the piano.... etc, just like reading a map.

With another amp, the whole sound (singer+music) just at the same place, in a wall just right infront of me. No "depth" in music.

All the people there loves the amp with that 3D Depth sound reproduction. They say the more expensive an amp, this effect is more obvious (is this true?)

We are not talking about digital delay thing here, just plain analog amp compared with analog power amp. No time delay, no fancy processor.

What makes an analog audio amp can make a good "depth"? Is there a trick in the designing process?
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Old 2nd September 2004, 03:57 AM   #2
cowanrg is offline cowanrg  United States
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i sell the stuff for a living, so the most non-technical way to explain it is this...

a cd is recorded in stereo, or at least mixed in that way. if it is live, or mixed in a studio environment, there is depth and a 3d recording. certiain things are farther away than others, and some things are more left than others.

so simply, if the reproduction is accurate, these sublteties should come through with the playback as well. some speakers are very good at doing this. in my opinion, it has to do most with the speakers, then the amp, then the source, then the preamp.

but the amp and speakers have a huge role in this.

ive had several cds where the recording is such that certain notes actually come from behind you. there are a couple of DVD-audios where this happens in 2-channel. this is just a phasing thing. with my system, i can hear things on the side of me, and sometimes (rarely) behind me. it is not uncommon to hear things further out than the speakers, or behind, or in front of them.
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Old 2nd September 2004, 05:23 AM   #3
Eva is offline Eva  Spain
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Quote:
Originally posted by cowanrg

so simply, if the reproduction is accurate, these sublteties should come through with the playback as well. some speakers are very good at doing this. in my opinion, it has to do most with the speakers, then the amp, then the source, then the preamp.

but the amp and speakers have a huge role in this.
I think 95% of that effect is lost due to room acoustic issues, 4.9% is lost due to lousdspeaker issues and 0.1% is lost due to electronic issues, assuming there is a suitable recording as a starting point. Studio-mixed recordings are not likely to contain that kind of information

The 44.1Khz PCM format itself also forces some information loss since phase differences between channels are quantized in 22.7uS increments [sampling period] while analog recording can store almost infinite phase differences between channels. Anyway, 44.1Khz PCM stores enough information to make the effects clearly perceptible

It's not so hard to create such recordings, just place two identycal mics with its sensing elements about 20cm away one from the other and record each into a channel. Move sound sources around the mics and then listen to the results with matched speakers preferably outdoors or in a very dead room, or also with headpones

Even cheap electronics tends to have enough channel matching and separation to not alter that phase-difference information, but selling electronics is much easier than selling loudspeakers or room treatments. Actually I only enjoy to listen music outdoors, rooms are very very frustrating, particularly smaller ones

Most 'audioplhiles' know nothing about acoustics and blame electronic equipment when his wife moves a carpet or something in the listening room and 'something changes in the sound'. Sound waves interact with every single object or surface in the room before reaching our ears and these interactions are somewhat 1,000 times stronger than the ones caused by electronics...
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Old 2nd September 2004, 05:54 AM   #4
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The room is the same, the speaker is the same, the position is the same, the AC line is the same, the CD is the same, the cables are the same, the crowd is the same, everything is the same.

Just change the amp, then other amp, then other amp.

Why one amp has more "Depth" than the other? How to make this?
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Old 2nd September 2004, 06:25 AM   #5
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Quote:
Originally posted by lumanauw
The room is the same, the speaker is the same, the position is the same, the AC line is the same, the CD is the same, the cables are the same, the crowd is the same, everything is the same.

Just change the amp, then other amp, then other amp.

Why one amp has more "Depth" than the other? How to make this?
I know exactly to which you refer. I experience it while testing and evaluating various different tube amplifiers while testing them on my new speaker designs. I think it has to do with the way the phase of the signal spectrum gets distorted within the amplifier circuit between input and output. One term that describes such an instrumental (electronic) effect is differential phase where the propagation time of the signal through the amplifier is different at different frequencies dependant on signal amplitude at the moment in time. The presence of negative feedback or not can effect this as well. The output transformer and any interstage transformers can also effect this. The trick is to get it 'right' when building an amp design. Many try, far less succeed. I think having the shortest signal path i.e. the least amount of stages to corrupt the signal is part of the path to such desired 'transparency' in the sound. Well regulated and suitably bypassed power supplies to each of the active gain stages are also part of the way to better sound.
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Old 2nd September 2004, 10:07 AM   #6
dnsey is offline dnsey  United Kingdom
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Interestingly, the '3D' effect is sometimes more obvious in amps with relatively high crosstalk between channels. The effect has been exploited in several psychoacoustic processors, but I haven't yet come across an explanation for it.
Certainly, one of the best defined soundstages I've heard came from an ancient Armstrong amp with audible crosstalk, and I once had a startling experience of realism (in this respect) from an ultra-cheap Amstrad music centre which I was repairing for a friend.
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Old 2nd September 2004, 06:30 PM   #7
MikeB is offline MikeB  Germany
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Quote:
Originally posted by Eva


The 44.1Khz PCM format itself also forces some information loss since phase differences between channels are quantized in 22.7uS increments [sampling period] while analog recording can store almost infinite phase differences between channels. Anyway, 44.1Khz PCM stores enough information to make the effects clearly perceptible

This is not completely true, even with this quantisation you can have
much more exact phasing due to antialiasing. I used this effect in
my 3d-soundroutines, where i had the problem that i had to use
accurate phaseshifting with 22khz output. With hires interpolation
between samples (phaseaccurate) you completely knock out this
problem. This antialiasing happens automatically when converting
from analog to digital. The phaseshifting is very subtile, but the brain
uses this information to locate the sound in a 180degree-circle.
Given an eardistance of 20cm, a sound 10meters away, rotated 90deg
you get a phaseshift of 1.16ms, going to zero if the sound is exact
in front of you (or behind)

Elevation of the sound and detecting if its front/back, does the ear
by checking reflections and filtering inside the ear, even the reflection
from shoulder is important.

Mike
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Old 2nd September 2004, 07:19 PM   #8
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So called 3 D sound have three requirements : amp with very low crosstalk, very low distortion ( mainly at low output levels ) and record, which is made directly ( which is not mixed from many track, 'cos it is for this effect grave).
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Old 2nd September 2004, 09:12 PM   #9
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"3D" is just another subtle description of so called "sound stage".

A tend to back up behind UE's words.

Also many loudspeakers can't reproduce a "soundstage" very well, and there are even super expensive loudspeakers which don't even have a linear frequencies/time -domain reproduction which is even a much worse problem than for amplifiers.

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Old 2nd September 2004, 10:28 PM   #10
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I have a couple of 15" KLH 'linear dynamics' model speakers and they reproduce the 3D sound effect really well, even through just one channel. They are 4Ohm speakers though. Eva has made a good point that the room acoustics have the most to do with the sound.
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