Re: [linux-audio-dev] [OT] Info required: FLAC on W*****S

On Thu, May 20, 2004 at 08:00:31AM +0200, Jens M Andreasen wrote: I do not see such a statement in the FAQ. It is indeed possible at low frequencies and using 2 speakers, to create a sound field that has a gradient that points outside the line connecting the two speakers. When you do this with only two speakers, the resulting image will be very unstable as there is a strong standing wave component. Ambisonics uses similar techniques (in fact using all speakers for any particular direction) to correctly reconstruct the sound field. What the FAQ does explain is that the old 'quadrophonic' systems and the new 5.1 and 7.1 setups use pairs of speakers to position sounds between them, and that this simply does not work except in the front direction. Again, the FAQ does not state that '4 channels is superior to 7'. It does say (see above) that the ITU n.1 systems are based on false assumptions, while the Ambisonic way of doing things is based on solid knowledge about human hearing mechanisms for its principles and on solid mathematics for its implementation. Do not confuse '4 channels' with '4 speakers'. The 4 channels of an Ambisonic B-format recording do *not* correspond to speaker signals at all. They are decoded in function of the actual number and layout of the speakers. In fact you can decode them for reproduction on a 5.1 or 7.1 layout if you want. It's interesting to note why the ITU n.1 layouts are what they are. They where created originally for sound reproduction for movies. - The Centre channel was necessary in order to have reasonable positioning of the dialogue, which normally happens on-screen, In particular in the front rows the audience would otherwise see two front speakers with a very wide angle between them, and this simply doesn't work. In fact you do not need a separate *channel*, a separate *speaker* fed with the right signal will do as well (or even better). This was not realised at the time, and anyway there are practical advantages to having the dialogue on a separate channel (it allows for multi-lingual distribution). For realistic reproduction of music, the centre channel (again I mean *channel* and not *speaker*) gives a completely artificial emphasis to front sounds, and should never be used. - The separate VLF channel. In movies this is used for effects only. Why is this a separate channel ? Not because there is no directional information at low frequencies, but just beacuse of the technology limitations at the time these systems were developed. With analog magnetic recording (the norm at the time), you can not combine high- intensity VLF sound with the normal signals without introcuding lots of distortion. Also, as long as this is used only to reinforce visual effects and realism doesn't matter, it's cheaper to have a few big subwoofers than to require extreme LF performance for all speakers. But without the visual cues which distract your attention, this simply doesn't work. So why, you may ask, has this become the commercially dominant technology ? The answer is very simple : for the same reasons that Windows is the dominant OS for computers. The big multimedia companies know very well that there is a lot more money to be made from 'home entertainment' than from high quality sound reproduction. And since the movie industry, the music industry and the equipment manufacturers are nowadays one and same, the result is easy to predict. -- FA