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| Section 1: An Overview |
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| About the organization |
The Audiophile Recordings Trust is a non-profit making organization, based in the UK, comprising a small group of audiophiles and audio engineers. |
| Our Primary Aims |
To promote the use of advanced recording and playback techniques, particularly 360 degree systems, to accepted audiophile standards. To produce and make available multi-channel recordings to promote our aims. To demonstrate new audiophile sound formats to audiophiles and recording companies. |
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| What do we
think is the |
Ambiophonics and the 360 degree version, Panambiophonics. This is the only sound recording and playback system that is capable of accurately reproducing sound images based on correct psycho-acoustic principles |
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| What is wrong with traditional stereo ? |
The ear relies on several subtle mechanisms for detecting the location of sounds, briefly summarized as follows: 1. The relative sound pressure level between the left and right ears. This is the obvious mechanism used by traditional stereo. A large signal from the left channel gives the impression of an image from the left. This mechanism also involves the presence of the listeners head which affects the relative sound levels at each ear. 2. The time delay of sound reaching each ear. This produces complex frequency dependent responses used by the ear to locate sources. This again involves the shape of the listeners head which produces diffraction effects and physical separation. 3. The pinna (outer fleshy part of the ear) produces yet more complex effects which are used to locate sounds. We can all locate sounds with just one ear and this response is due to an amazing mechanism involving the pinna. |
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Traditional stereo (2 channels, speakers placed 60 degrees apart) fails on 3 counts by largely ignoring the above mechanisms |
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| Failure Number 1 |
Assume a left sound source. This produces a signal path to the left and right ears producing time delays and shadowing effects due to the head. Let us use a stereo recording microphone with a left and right microphone placed either side of a head shaped sphere or, even better, a dummy head. With this technique, we will record, on the left and right channels, a good representation of what each ear is receiving with all the required stereo cues in place. No problems so far but how are we trying to play these signals back ? In a traditional stereo setup the left channel is played back through the left speaker, sound reaches the left ear exactly as required but then carries on to produce a signal at the right ear. This signal to the right ear from the left channel is not present in the original live session. The right ear should only hear a signal from the right channel. In Ambiophonics this effect is called the unwanted stereo crosstalk signal. The same stereo crosstalk problem will occur from the opposite right channel to the left ear. Of the 3 sound location mechanisms used by the ear mentioned above, 1) is partially reproduced but 2) and 3) are completely compromised by stereo crosstalk. |
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| Failure Number 2 |
The Recording Techniques used for most recordings do not capture natural stereo image information during the recording process. Multiple microphone systems with multichannel recordings mixed down to a stereo channel can only use mechanism 1) to artificially place sound images. This leaves audiophiles with the uneasy and stark realization that almost all the recordings available to them are effectively synthesized under the control of the engineers involved in the final mastering processes. In the past this may not have been an issue because of the limitations of the final playback technique (traditional stereo) mentioned above. These limitations are continued, of course, in the production of multichannel home theater sound tracks. Some record labels however, do produce recordings with natural stereo content, Chesky Records, for example, and they deserve to be popular. |
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| Failure Number 3 |
After 70 years of development a traditional stereo recording can only cover a 60 degree front sound stage. Very obvious but very true ! If you think you can hear anything greater than this, it is not real. There have been other formats, i.e Ambiosonics but they are psycho-acoustically flawed and rely on complex recording techniques. |
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| Enter Ambiophonics ! |
To overcome traditional stereo's shortcomings we have to do 2 things. 1. Make recordings that capture natural stereo information. We dealt with that above. 2. Remove stereo crosstalk during playback so that we can reproduce the correct signal to each ear. Ralph Glasgal of the Ambiophonics Organization, (www.ambiophonics.org) has pioneered 2 methods of crosstalk cancellation. There is ample explanation on his website but we will summaries them briefly below. |
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| The Stereo Dipole and |
This is the simplest 'classical' method that we use as a reference. The stereo pair of speakers is placed at 20 degree overall separation in front of the listener and a central sound absorbing panel is placed between the speakers and the listener. This simply stops the left signal reaching the right ear and the right signal reaching the left ear. It is not perfect, since there is bound to be leakage within the room, but it is effective in the critical range above 500 Hz. Further room treatment in the form of sound absorption will also help, as it helps with traditional stereo. |
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| Digital Signal Processing |
Crosstalk cancellation can now be achieved at relatively low cost and is potentially a viable alternative to the physical barrier. For audiophile standards however we recommend the physical barrier for crosstalk cancellation. This is a larger topic, more information is available in Section 3 |
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| And now Panambiophonics ! |
Double everything up in the reverse direction and we have full and natural 360 degree recording and playback. No simulation, no artificial reverberation for the rear channels and no other processing required, just how audiophiles like it ! |
| A further improvement - |
The immediate left and right side images can sound indistinct in many circumstances. 4 channel Panambiophonic recordings can be improved markedly by the addition of Left and Right side cardioid microphones. Playback is carried out using 6 speakers with left and right side signals approximately 15dB below front and rear channels. A limited low frequency bandwidth from 350Hz upwards is all that is required enabling the use of small satellite speakers. |
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| What is the bottom line ? What can we achieve ? |
1. Imaging is improved markedly with a more open and less confusing sound, especially with large sound stage, complex sources. Once you hear the improvement you will not want to go back to traditional stereo ! 2. A wide sound stage, 360 degrees with 4, or preferably 6, channels and good height information. 3. An original recording made using dummy heads or spheres is fully compatible with traditional stereo recordings. This is very important from a compatibility point of view and is not the case with previous surround sound formats. It also gives excellent binaural recordings for headphone listening. 4. It can be tried very cheaply, just make some dividers and buy known, good CD / SACD recordings with natural stereo recorded. This will improve your sound much more significantly than the effects of expensive cables, filters etc etc. 5. Professional pc based sound equipment is capable of excellent high quality recording and playback in multichannel high sample rate formats which can now be reproduced onto DVD-A disk. These can be used to promote the benefits of Ambiophonics and any other untapped resources currently not available to the audiophile. |
