Holographic imaging

Tbg, sorry, but, **there is no doppler effect in an amplifier**! If a designer of a 'holographic processor' tells you something like that, turn around and run as hard as you can!

You have propagation delay in any amplifier circuit but that does not create doppler effect, in either an amplifier or a preamp. It is possible to get some in a loudspeaker driver that has wide range and high excursion, but that can be dealt with by proper speaker design. IOW, if 'doppler effect' is really the reason, its at best a fix for a problem that does not exist. At worst--? Certainly such a 'process' can be considered a distortion in the overall output...

I haven't heard the H-Cat gear. I am dubious of these claims. How does one determine just where in the circuit these errors occur? Does the circuit allow for the approporiate correction to be applied in each instance of error, and is that necessary? If in fact these errors are in evidence, wouldn't a (with prejudice aside) digital input read compared to a digital output read and correction make more sense?

Musicnoise,

Thank you for understanding at least part of the science behind Doppler interference in an audio system. Of course none of the above is "moving" (ignoring the speaker cones for now).
However, the electronics used to amplify the audio signal can alter the speed and therefore the pitch of what you hear. Since the effect is based on the relative distance between the sound object and the observer - it is not necessary to move any of the sound objects - just the observer. You and your system are the observer. Now since I don't expect that you are moving toward or away from your speakers, that leaves the delivery speed of your system.

Once you accept the fact that you can alter the speed of your system electronically and therefore emulate the physically induced Doppler effect - then everything will fall into place.

How can you induce Doppler electronically? The easiest way is to do this is by adjusting the playback speed on a tape deck while you are listening to music. An increase in playback speed (velocity) will cause an increase in pitch.

Moving toward a sound object PHYSICALLY will do the same thing. So you can see that it is possible to cause an effect (electronically) that we normally associate with the physical world.

I know your saying to yourself "but I'm not listening to a tape deck with poor speed control - I'm listening to my very stable digital front end."

Here is the problem – the analog amplifier circuitry in your system contains very small variations in speed (velocity) as the audio signal travels through your entire system and exits via you speakers. How can you change the speed of a signal as it is being amplified? All you need to do is alter the gain by a tiny amount and you have altered the speed.

Take for example you are listening to a recording of a live concert. You adjust your volume control for a “normal” listing level. You feel like you are in about the 10th row back. Now you decide to turn up the volume and you feel like you are in the front row (closer). If you then turn down the volume much lower so you feel like you are 20 rows back.

By adjusting the gain of your system – you have zoomed in and out of the scene. You have electronically moved the stage closer and farther away from you. Now, here is the most important aspect of this example to grasp – what I described was an action taken by you in your living room (setting the volume) to simulate the 3 relative listening positions at the concert hall. Now picture the actual physical repeat of this example. In other words you ARE at the concert hall. You are sitting in the 10th row and listening to real musicians play through the medium of air. There is no change in pitch / no Doppler. Now you get up and walk toward the stage to sit down in the front row. Again you listen from the front row (louder) but again with no change in pitch / Doppler. Everything seems normal and stable so what is the point?

Here is what you missed. It is not the location you listen from that changes the pitch. It is the movement you made between the locations that introduced Doppler. In other words when you walked toward the stage – the pitch of all the instruments was increased. If you were to walk toward the back of the hall to sit in row 20 you would experience the lowering of the total pitch of the music.

To tie this into what happens in your living room – the act of walking toward the stage IS the same as you turning up you volume (as it is being adjusted). Once you stop adjusting the volume – you are again stable and free from Doppler.

In case you think this is BS – here is a way to prove it in you own system.

Get a reference CD of pure tones and select a 1Khz tone to play in your system. Set you volume control to some “medium” level. Now turn the manual volume control up and down rapidly (wiggle).

What do you hear? Besides the obvious change in loudness – yes the FREQUENCY goes up and down.
Your 1000 hertz tone can drift up to 1100 hertz and down to 900 hertz depending on the speed and depth of the physical changes to your volume control. (Turning it up and down slowly will give almost no perceived change in pitch)

How is it possible to alter the frequency just by changing the gain? It is because the gain represents the efficiency of the delivery system and is directly related to the velocity of the traveling signal. Increasing the gain will accelerate the velocity and decreasing the gain will de-accelerate the velocity.

This all boils down to the involuntary changes in gain that occur in your system when you are not making adjustments (yourself). These microscopic changes in gain happen all the time while you are listening and your brain translates (correctly) that the relative distance between you and the sound objects is drifting and unstable. This wobbling distance is actual Doppler. As a result your “scene” is out of focus and bloated. This produces harmonic distortion on a scale that is far below the radar of all modern test equipment. However your brain has no problem picking up on this effect. It immediately recognizes that “this is not real”. In order to convince the brain that “this is real” – you most stop the Doppler effect from happening during the amplifying process.

BTW – the natural side effect of stopping the Doppler is holographic imaging.

Regards,

Roger

Roger_paul,

Interesting.

Is doppler effect in an amp a different problem than the one solved by application of negative feedback? If so, how much is it different in terms of the effect on the sound?

Thanks.

Mapman,

The Doppler effect in amplifiers is not actually a different problem than the one "solved" by NFB. It is the root of the problem that NFB cannot fix by design.

NFB is a servo system that only works for steady state sine waves. Not for complex music.

Even if you use massive amounts of NFB - you cannot remove Doppler. It is the wrong tool.

Regards,

Roger