Huge speaker fakes the record room acousticsn

Status
This old topic is closed. If you want to reopen this topic, contact a moderator using the "Report Post" button.
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.
 
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.
 
Last edited:
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
 
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.
 
Last edited:
not to beat a dead horse, but there are a few points worthy of comment, all meant in a light-hearted manner

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 :p, 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. :rolleyes:
 
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.
 
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.
 
Last edited:
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
 
Hello Key,

I have revised the rest of the Holophony.net site in the last days. Was good occasion for improve the content besides my translation skills, I hope. See per example such sentences:

The main advantage of wave field synthesis seems hardly take in account until. In difference regarding all other audio reproduction principles the synthesis provides access at each component of the sound event. No other principle is able for manipulate during playback direct wave, first reflections and reverberation in different manner. All conventionally procedures inseparably merge together the components on the recording site.

That’s important thoughts well translate, I hope.:spin:

Regards Helmut
 
I was looking it over last night and it looks like you've cleaned it up a little. I am still working through it and re-writting it as I go. Kind of inspired me to test out some ideas so I got a little distracted and was testing them/implimenting them before I forgot.

Anyway I will go through and double check for you.
 
I was looking it over last night and it looks like you've cleaned it up a little. I am still working through it and re-writting it as I go. Kind of inspired me to test out some ideas so I got a little distracted and was testing them/implimenting them before I forgot.

Anyway I will go through and double check for you.

... I have completed today the revision of the Wave Field Synthesis and Holophony site. Simple trick I have apply, was inserting english version into google translator and change the words till meaningful german translation arise. Was a good exercise for someone without all english laguage education. Is a lot sense now in the text, read the page will possibly head change your view regarding audio reproduction. But if further faults in the translation, advices are welcome.


Regards Helmut


text sponsored by google translator:headshot:
 
Hello,
currently I work at the problem description. German is finished, the english translation is in work:

____________________________________________________

Two ears - two loudspeakers?

The difficulties of the audio reproduction

Many of the stereo freaks believe devoutly, as far as all components in the transmitting chain perfect, also the reproduction must be perfect. Would two solid state microphones grasp the sound field at the listeners point in the recording room, the loudspeakers must deliver genuine like reproduction. After all, we have only two ears. Yet important physical interrelations remain unconsidered in that view. All we can hope is tonal accuracy, true spatial audio will never happen at the traditionally procedures. Those can count for lost already during the recording process.



The spatiality of recording

In the recording room we are hit from the direct wave front and its reflections from all possible directions. In the azimuth level occur interaural time differences (ITD) between listener’s ears, dependent from starting position of the wave front or reflection.
That’s an important cue, yet only one part of spatial information. ITDs evaluate between app 100 Hz and 3, 6 kHz very accurate. Beneath, the differences in phase too small, beyond the result become ambivalent, because more as one wavelength fits between the ears. Further ambivalence arises regarding front and rear. Same ITD`s occur whether the source is in front or behind the listener. Over and above, ITS`s absolutely independent from elevation of the source, alone the run time detection works in horizontal plane.
Thus, for correct spatial localisation of any sound source we need additionally cues. We use the interaural level changes ILD, which arise by diffraction from head and shoulders in upper frequency range as well as resonance effects at the outer ear. The individual molding of the pinna produce resonances, which change depending the elevation angle. Our individual listening experience, caused by the different formation of head and pinna, provide excellent determination of the source position in all three room dimensions as long as that Head Related Transfer Functions deliver coincident signals regarding the ITD cues.
Our recording technology though doesn’t work so excellent by far. Two microphones on listener’s position receive correct time differences, but the correct amplitude response disappears during record. Spherical micros work widely independent from source direction, cardioids loose level in upper frequency range outside of its axis. In any case such directive effect cannot produce the angle dependent notches and hills in level which provide our human perceiving system for accurate source detection. Later, during playback, we spend a lot of money for the last 2 dB linearity in frequency response, but during record process we tolerate level differences of 20 dB and more compared with the signals at human eardrum.
Besides, without correct Interaural Level Differences (ILD), the recording unavoidably reduced onto horizontal plane. Moreover, important information regarding the source direction going lost, because the strong selective effect of the Head Related Transfer Function never become include in transmitting chain. That’s less important for source position itself. In front range ILD changes small, at least in the horizontal level. Yet the first reflections encounter the listener from above, behind, and from all possible other directions. Without correct notches and hills in frequency response the reproduction contain wrong cues. Amplitude cues sometimes direct in contradiction regarding the time cues. Listening fatigue is only one of the results, because the spatial distribution of the first strong reflections is one of the most important cues for audio perception. Subjective perceived volume, speech intelligibility and estimation of the source distance strongly disturbed by wrong cues. Producing the spatial impression by reverberation remains hardly usable attempt. Such late reflections provide important cues regarding reflective behaviour of the recording room, yet arrive from all directions there. We hardly able for allocate concrete direction thus for the reverberation tail.
Studio productions normally doesn’t recorded by microphone pair, each signal become its spatial position according the intention of the producer during down mix. Yet the problems are the same. All source signals shared between the speakers by the pan pot position, all spatial impression ought to include in reverberation. Only sometimes such processes produce proper early reflections. Then we are able for perceive satisfying spatial perception, but we cannot provide those reflections from the nearly infinite amount of source positions, which arise in the recording room, but rather from few loudspeaker positions.

________________________________________

Next chapters "The perception of the phantom acoustic source" and "Two rooms in one record" in some days.

Any advices regarding the first part?

Regards Helmut
Wave Field Synthesis and Holophony
 
Next chapter:

The perception of the phantom acoustic source

All conventionally audio procedures, also the surround formats, produce phantom acoustic sources, which perceived between single loudspeakers. Those sound sources don’t real thus, but build up in brain by psychoacoustic connection of both ear signals. Unfortunately, such sound sources don’t behave as real sound sources. We cannot keep our ears at it, differently regarding real sound source the phantom source moves with the listener’s position. In fact, we don’t hear a sound source, but two.
For perceiving same direction, two phantom source loudspeakers must produce much more differences between signals as real sound sources. As example, at 30 degrees azimuth angle real acoustic source causing interaural time difference of 0.3 milliseconds and for instance 5 dB interaural level difference. Radiated from two loudspeakers, such values generate only approximately 10 degrees angle in Azimuth for the perceived Phantom acoustic source. For 30 degrees we need 1.5 milliseconds and 18 dB level difference. [2]
The reason for that loss of spatial impression is crosstalk between the ears. The signal of the left speaker attains not the left ear alone. With detour around the head the wave fronts reach the right side and converse. That exalts the Interaural Cross Correlation Coefficient IACC, one of the most important values regarding our spatial impression. We sense a sound event as spatial, if the signal difference between our ears as high as possible. As far as both signals are utterly different, the IACC is zero, there is no correlation between the signals. If both signals are the same, for example at mono headphone playback, the IACC value is one. At 0.3 a sound source in free environment reach the most possible difference, if the wave fronts reach us from circa 55 degree azimuth angle. In acoustical famous venues a lot of the first reflections come from that area. If the direct sound source at the other side, such reflections known as “acoustic attraction”, engender the gooseflesh when the horns initiate in the Brahms concert.
Conventionally loudspeaker reproduction cannot originate such experience, because the right box is only app 30 degrees off from median axis. Yet, the more closely spacing causes less IACC, consequently less attractively. Also in the concert hall the central ceiling reflections doesn’t improve spatial impression. All or part such central reflections are contra productive sometimes. Well educated architects know that and try leading such wave fronts sideward. Because crosstalk between the ears our stereo loudspeakers cannot reach IACC below approximately 0.6, the concert hall experience remain out of reach thence. All experiments for produce sound sources outside the loudspeaker base by inverse phase and other tricks in vain and dilettantish. During playback, alone the playback room able for produce sound sources in that range by its own reflections. Yet such reflections are disturbing in most cases, because the sound detours very different regarding the recording room.
Without the correct spatial distribution of the first reflections drop away important cues for estimate distance regarding direct sound source. The starting point of phantom source in any case between the boxes, not before and not behind that line. That’s comprehensible, if we look at different listener positions. For example, if in the concert hall the violin placed exactly before the timbale, we hear both instruments from same direction. If we move now to the right wall at the concert hall, the violin will perceive clearly left from timbale. By phantom source reproduction at home yet, both instruments remain on the same position, independent from listener’s position. Both sound sources feature the same starting point. There isn’t realistic therefore, praise the excellent deep impression of the phantom source reproduction as like as the genuine. The phantom sources between the speakers, not behind and never in front.

Though, I have to admit in the real world also we cannot estimate the distance regarding sound source directly. The signal differences between both receptors in audio we use for determination of direction and not, as like at the eyes, for estimate the distance. For audio the most important indication is the volume, loud sources nearby in normal case. But phantom acoustic sources cannot be more converge at the listener as undirected radiating loudspeaker boxes. Those cannot provide better direct wave / diffuse field relation as the loudspeaker itself in playback room, realistic proximity effects not reachable thus. That restriction underrate widely, nearby sources or reflection sources supremely important for spatial impression as well as emotionally impact of perception.



Any input or remarks?

Regards H.
 
Hey Helmut,

I have two edits that I started of your site. I got a little frustrated when the translation changed and I was half way done with the first one. It seemed like I had to start all over from the beginning. Anyway those translators can really chop up the sentence structure and make it hard to know what your are trying to say.

Maybe if you can run the text through 2 translators and I can make an edit from those. It would help me feel out what you are trying to say better in certain cases to have more than one translation.
 
Hello Key

I was without of hope for your further assistance, because I know, it’s a hard work. I am very glad about the improved version of the main page. Yet at the German side I have seen the importance of problem description. Without describing the problems nobody interested at new solutions. Thus I have inserted today additional link “Problem description” at the home page. Your improved translation for main page isn’t changed.
I know, there are some mistakes in the new text and will try to improve it. I would be glad if you assist a little, if my attempts without success.

Regards from Germany, Helmut
 
Status
This old topic is closed. If you want to reopen this topic, contact a moderator using the "Report Post" button.