Huge speaker fakes the record room acousticsn

[Key]

Come on can't I be an ignorant American in peace.

See the difference in Canada is there are a lot of schools that speak French and get the kids to start speaking it at an early age. In the US we wait till they are about 13 or 14 and then try to teach a language to the person. I think you can see the obvious disadvantage to that. I guess I could spend more time with the Spanish speaking community and learn that way - I had a friend who was determined like that - but again America seems to be a very segregated community.

I could probably edit the translation for you syntheticwave. But I can not translate directly only intuitively feel the meanings of the sentences out. More than a couple seem like they need rewording.

[Key]

Well deciphered the first section - I think. I just hope I am not messing up the meaning of anything.


Summary

The animation shows the propagation of the (black drawn) direct acoustic wave and its first reflections in the (large outer) recorded room. Their starting points seem to be the (multicoloured) mirror sources behind the recorded room's walls. It's spatial distribution is essential for our spatial perception of the sound event but conventional loudspeaker reproduction procedures cannot restore this complex spatial structure. The reduction into a few transmission channels inevitably causes a significant loss of spatial information.

This page describes a different way to restore the mirrored sources closely to its correct positions. Just like the recorded room creates all reflections from the point-source of the audio event, a sound field synthesis restores the reflections from the direct sound and information regarding the recorded room's properties. This ?“Holophonic”? approach relies on the principles of Wave Field Synthesis, which was described by Berkhout and the University of Delft in the 1980s. Kirchhoff- Helmholtz- Integral prove the possibility to restore the complete sound field in theory, but some practical constraints have made that goal unfeasible until today. A number of scientific institutes have implemented this theory very successfully, but have reduced it to only one single horizontal loudspeaker row around the listener. This limits the principles to the horizontal plane of the listener.

The “Holophonic” solution is based on a large-scale frontal WFS Loudspeaker screen - colored magenta in the animation. Such an arrangement can truly work in all three room dimensions. Within the near field of such a huge diaphragm the playback room's acoustics become a trivial matter. Its reflections no longer must be eliminated by strong damping, but are included purposefully in the synthesis. The loudspeaker screen aligns the direct wave and its first reflections in the playback room to form the illusion of the recorded room's reflections in time, level and direction. They arrive, reflected from the playback room walls, to the listener’s ears in the same manner they would to the ears of a virtual listener in the recorded room.

In this respect the described procedure differs fundamentally from the realised WFS Approach of the scientific institutes, in which the transmitting chain ends on the loudspeakers, not on the ears of the listener. The Holophony procedure subtracts the additional delay times and level changes in the playback room by providing congruent signals on the dedicated points in the recorded room and the listeners ears in the living room. The audio signal no longer changes two times - in the recording and in the playback room - which is inevitable using conventional principles. If the point of reference in the recorded room changes, accordingly all positions of the virtual sound sources in the model based approach change. So the listener can walk within the virtual acoustics of the recorded room in the near field of its WFS- Loudspeaker screen by means of a remote sensor.

[syntheticwave]

Originally Posted by Key

Well deciphered the first section - I think. I just hope I am not messing up the meaning of anything.


Summary

The animation shows the propagation of the (black drawn) direct acoustic wave and its first reflections in the (large outer) recorded room. Their starting points seem to be the (multicoloured) mirror sources behind the recorded room's walls. It's spatial distribution is essential for our spatial perception of the sound event but conventional loudspeaker reproduction procedures cannot restore this complex spatial structure. The reduction into a few transmission channels inevitably causes a significant loss of spatial information.

This page describes a different way to restore the mirrored sources closely to its correct positions. Just like the recorded room creates all reflections from the point-source of the audio event, a sound field synthesis restores the reflections from the direct sound and information regarding the recorded room's properties. This ?“Holophonic”? approach relies on the principles of Wave Field Synthesis, which was described by Berkhout and the University of Delft in the 1980s. Kirchhoff- Helmholtz- Integral prove the possibility to restore the complete sound field in theory, but some practical constraints have made that goal unfeasible until today. A number of scientific institutes have implemented this theory very successfully, but have reduced it to only one single horizontal loudspeaker row around the listener. This limits the principles to the horizontal plane of the listener.

The “Holophonic” solution is based on a large-scale frontal WFS Loudspeaker screen - colored magenta in the animation. Such an arrangement can truly work in all three room dimensions. Within the near field of such a huge diaphragm the playback room's acoustics become a trivial matter. Its reflections no longer must be eliminated by strong damping, but are included purposefully in the synthesis. The loudspeaker screen aligns the direct wave and its first reflections in the playback room to form the illusion of the recorded room's reflections in time, level and direction. They arrive, reflected from the playback room walls, to the listener’s ears in the same manner they would to the ears of a virtual listener in the recorded room.

In this respect the described procedure differs fundamentally from the realised WFS Approach of the scientific institutes, in which the transmitting chain ends on the loudspeakers, not on the ears of the listener. The Holophony procedure subtracts the additional delay times and level changes in the playback room by providing congruent signals on the dedicated points in the recorded room and the listeners ears in the living room. The audio signal no longer changes two times - in the recording and in the playback room - which is inevitable using conventional principles. If the point of reference in the recorded room changes, accordingly all positions of the virtual sound sources in the model based approach change. So the listener can walk within the virtual acoustics of the recorded room in the near field of its WFS- Loudspeaker screen by means of a remote sensor.

Hello Key,

thank you very much, I can grasp it now much better. Its early morning in Germany, will change the text today on evening,

Kind Regards Helmut

[Key]

Man this next one was hard. Really I am supposed to be writting my own thesis. So it'll probably be a while before I can get back to this. Can someone else take a shot at the next one?




1. Holophony - A virtual 3D-copy of the sound field

Since the invention of stereophony there have been attempts to improve the spatial reproduction of a sound event with an increasing number of channels. Yet the sound source itself doesn't reproduce any spatial sound field; each arbitrary source may be regarded, at least from a certain distance, as a Mono source. That source isn't radiating equally in all directions and there is no way for an entire spatial sound field to be reproduced. The spatial sound field is only partially the result of the source signal's reflections in the recorded room. This complex reflection pattern would be restored completely if we start from such thought:

If we build a closed cabinet around an ideal place in a concert hall, but perforate it close-packed, the acoustics of the concert would hardly be disturbed. If each of the holes contained an inward facing loudspeaker, steered from its own microphone on the other side of the wall, the acoustics effects would remain the same inside the box. Placed in our living room at home these speakers would provide a perfect copy of the original sound event.

Yet a problem would arise because such a number of discrete channels is hardly transferable. Every speaker radiates a slightly different signal, but when examined more closely we find that the waveform doesn't differ from hole to hole; only the arrival time is different. Therefore all of the speakers' signals are producible from a Mono signal of the sound source if you know its position in the recording room to calculate the delay times. For the spatial reproduction we not only need to restore the sound source, but also all of the reflections in the recorded room must be recovered as well. Since the reflections are singing no other song than the tenor, we can synthesize all of them from the direct source signal if their starting points are known. If we know the position of Tenor in the concert hall and the concert hall's properties, we can calculate the reflecting points. Now we can produce all the loudspeaker signals by a computer synthesis at home from the dry mono signal of the sound source.

However, the spouse acceptance factor would be very poor for a person who wants to populate a living room's walls with loudspeakers. But if we use the reflecting surfaces of the living room, combined with established sound projection principles, a flat loudspeaker screen in front of the listener, possibly behind the picture screen, would be sufficient. But for Holophony the loudspeakers would not be merely emulating other loudspeakers, but the source itself including the recorded room's sound field. In the near field of the huge resulting loudspeaker, the playback room's acoustics has very little influence on listening conditions, so the recorded room's acoustics may be recovered in an untreated room.

Today most audio recordings don’t have any genuine captured acoustic events. The records are a product of art, sometimes appearing more "perfect" than a genuine acoustic event. Holophony offers new creative possibilities, without the inconsistent cues of conventional audio reproduction, described in the next chapter.

[syntheticwave]

Hello Key,

That was really a lot of mistakes. It’s the asset of the communist time; we old East Germans have only education in Russian language. I will improve my English in the revision of the next chapters. But the introduction and the first chapter was the most important. Thank you for help again; the text is uploaded on the www.holophony.net site now.

H.

[chrisb]

not to beat a dead horse, but there are a few points worthy of comment, all meant in a light-hearted manner

Originally Posted by Key

Come on can't I be an ignorant American in peace.

I must resist temptation to reply to that

See the difference in Canada is there are a lot of schools that speak French and get the kids to start speaking it at an early age.

Well, jurisdictions certainly vary, but in our case (Vancouver Island, BC) our kids started in a French Immersion program at kindergarden, through to Grade 7, then progressed to "regular" program from Grades 8 onward.

And of course in Quebec & Newfielan , it could well be English offered as a second language.

While conversational and written second language skills can fade fairly quickly if not exercised, there is much recent study of efficacy and benefits of such early education in "wiring" the brain in ways that impact many other skills, long afterwards, and are very difficult to duplicate by even advanced studies later in life. After not using any second language after Grade 8 (1998) my son spent a total of 12 months backpacking in South East Asia, and South America during the past year and half, and was amazed at how quickly he was able to catch on to numerous local dialects.

party-time in 6 languages and across 14 time zones - I get sore in places I used to play, just listening to the details his mother is happy to never hear.

In the US we wait till they are about 13 or 14 and then try to teach a language to the person. I think you can see the obvious disadvantage to that. I guess I could spend more time with the Spanish speaking community and learn that way - I had a friend who was determined like that - but again America seems to be a very segregated community.

You might be better served learning Mandarin, so as to be able to read your next mortgage.

[Key]

I think I was lucky enough to steep myself in music as a second language at an early age. I think there is a parallel to learning how to compose and play music and learning a second language. While I don't think it's impossible to pick up an instrument once you are past a certain age, because there are some exceptions, it's something much easier to do during childhood which allows a lot of room for trial, error, and overall experimentation. I guess I don't think languages are taught as much as you just start talking in the language and eventually get it by making a lot of mistakes.

[Key]

Procrastinating by doing someone else's work. Hope I get some good karma for this. I guess I can chalk it up to learning about wave synthesis theory.



2. Phantom source problems

Tonal accuracy is the best that one can hope for in a traditional audio system; true spatial accuracy will never happen. Audio products should come bearing this disclaimer:

" WARNING: IMAGE PRESENTED IS LESS THAN LIFELIKE !"

Some audio purists are going to disagree with that quote of Barry Wills in Audio 08/1994 for sure. Today's amplifiers hardly produce distortion and some expensive loudspeakers produce a flat response from subsonic to ultrasonic frequencies in an anechoic chamber. What should be the reason for such a cheeky allegation? Let's quickly illuminate the facts:

The use of phantom sound sources is the main problem with conventional audio reproduction. The intended perception rests upon psychoacoustic principles, so the phantom sound source will disappear if we try to listen with one of our ears. The phantom source isn't really a sound source, it's actually the product of two sound sources. Thus, the sound from the right speaker will also hit our left ear and vice versa. This exalts the Interaural Cross Correlation Coefficient IACC, the most important factor for our spatial perception. We perceive a sound event as spatial if the signal differs between the ears as much as possible.

Besides, we can not radiate all of the wave fronts of a sound event simply from the direction which accidentally resides from a conventional loudspeaker. The Head Related Transfer Function mercilessly discovers the fraud if the angles of the wave fronts differ considerably. For true reproduction we need sound sources which we can localize precisely (at least virtually) at all of the starting points of the original wave fronts and its reflections in the recorded room. This is impossible with conventional methods.

Playback by discrete loudspeakers in any case is influenced by the acoustic behaviour of the playback room. In normal living rooms this confines the reflected sound energy of the direct radiated sound to less than 50 inches away from the loudspeakers.

[syntheticwave]

Originally Posted by Key

Procrastinating by doing someone else's work. Hope I get some good karma for this. I guess I can chalk it up to learning about wave synthesis theory.

Hello Key,

in my view your Karma is better than those of a flock of holy cows. I promise, we will share the acoustic Nobel Price.

If you are reading the next chapter you will see, the wave field synthesis principle is really simple, and more nearby the native perception principles as all multichannel procedures.


Kind regards Helmut

[syntheticwave]

I have rework the Wave Field Synthesis chapter today, hope for less mistakes in translation. If not so, this little animation describe the whole procedure.

Regards H.