Huge speaker fakes the record room acousticsn

[Key]

Originally Posted by syntheticwave

Hello Key,

in my view your Karma is better than those of a flock of holy cows.


Kind regards Helmut

Haha thanks. Yeah I haven't stopped looking this over just still reading over some of it. Maybe your last edit will help me fill in some gaps.

[syntheticwave]

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.

Regards Helmut

[Key]

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.

[syntheticwave]

Originally Posted by Key

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

[syntheticwave]

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

[syntheticwave]

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.

[Key]

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.

[syntheticwave]

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

[syntheticwave]

Hello Key,

I have improved the translation, I self can understand it good now. Is uploaded at ""The difficulties of the audio reproduction"- link now, yet I would be glad for advices regarding content or translation.

Kind Regards Helmut