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New Home Theatre Solution
Many people want to enjoy the same kind of surround sound in their home that they hear in movie theatres. However, this is difficult for some, because home theatre systems with their multiple speakers require considerable installation space and are generally expensive. In addition, some people feel that having many speakers and cables detracts from the attractive appearance of their room. One recent solution to this problem are surround sound systems that use only two speakers, producing what is often called virtual surround sound. Both the surround effect and the sound quality from these systems have left much to be desired, but Yamaha has now achieved true, high quality surround sound from only two speakers.
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Definition of Conventional Virtual Surround
When sound travels from its source to our ears, we automatically sense where it is coming from by analysing and comparing (between left and right ears) three factors: time difference, volume difference and phase difference. These factors are determined by the shape and direction of our head in relation to the sound source. The mathematical function that describes these factors is called HRTF, for Head Related Transfer Function. By using HRTF, it is possible to reproduce the same time, volume and phase characteristics that occur when sound is produced from left, right, centre and surround channels in order to create “virtual” sound sources for each channel, even from two speakers. The technology used to do this is generally called virtual surround.
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Yamaha AIR SURROUND XTREME
Yamaha has developed new technologies and algorithms that make it possible to achieve 5 and 7- hannel surround sound with only two front speakers, and without using wall reflections. Unlike other virtual surround systems, you can actually identify precise sound locations as if there really were speakers for the surround and rear channels. What’s more, the sound is extremely clear, natural and realistic, noticeably superior to that of other systems.
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AIR SURROUND XTREME is unlike any other two-speaker home theatre system. With other “virtual surround” systems, you hear all of the sound in, at best, three locations in front of you. In fact, there is no real “surround” effect. When you listen to this Yamaha system, however, you can actually identify sounds located around and behind you. You hear clear dialogue and other sounds from the front, specific sounds from the other channels to the sides and rear, and smooth sound movement around you. For an explanation of how this was made possible, see the other side.
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1. World’s First 24kHz HRTF-Based System
HRTF (Head Related Transfer Function) is a mathematical function that describes the various factors that affect how we locate the sounds that enter our head through the left and right ears. When the HRTF for each ear is known, it is possible to synthesise various “virtual” sound sources from two speakers. Thus HRTF measurement is a vital factor in achieving two-speaker surround sound. HRTF measurement depends on four variables: the left/right, up/down and front/rear coordinates, and the frequency. Conventional HRTF measurements could be done up to 8kHz, which is insufficient data upon which to base the creation of realistic surround sound. Yamaha has succeeded in extending this capability to 24kHz, thus enabling the creation of more virtual sound sources, with greater clarity and immediacy. The sound field is wider, higher and deeper, and sound localisation is far more accurate.
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Conventional HRTF
(8kHz)
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Yamaha HRTF
(24kHz)
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2. Creation of a Sound Field Especially for Virtual Sound Field With conventional versions of virtual surround, the sound locations tend to be diffuse, so it is not really possible to tell where the surround channels are supposed to be. This can mainly be blamed on the reverberations added to emphasise the sense of distance and sound fullness working against the virtual processing. To overcome this problem, Yamaha developed a sound field that works in harmony with the virtual processing, allowing the sound locations of the surround channels to be clearly identified while still maintaining a full sound expression.
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Conventional Front 2-Channel Virtual Surround
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Yamaha AIR SURROUND XTREME |
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3. Optimised Movie and Music Modes
In order to experience the full surround effect, it is essential to be able to recognise sounds from the rear, not only from the sides. However, as the rear channel sound is greatly influenced by the shape of head, i.e., blocked by the earlobes, how to effectively deliver it to the listener has been one of the biggest challenges for conventional virtual surround systems. This is further complicated by the fact that the requirements for movie and music surround sound are different. Yamaha’s exclusive algorithms and technologies enable not only sound from the front and sides, but from the rear as well to be clearly heard. In addition, we have developed two modes that provide optimum sound with movie and music sources.
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Movie Mode
This mode emphasises the rear components of the overall sound, including the low frequency range. Distinctive rear channels with good bass are essential for full enjoyment of movie sound effects. In a scene where a helicopter is circling, for example, you can actually follow its progress around the room. No other two-speaker system is capable of this. You hear full surround effects that make you feel as though the sound is really wrapping around you. In addition to use for movies, this mode makes sports events sound much more realistic as well.
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Music Mode
This mode provides clear, high quality sound with excellent sound localisation, particularly in the front and to the sides. You will be able to determine the location of the singer and various instruments, just as with a multispeaker system. Use this mode for live concerts and other music programs. |
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4. Stereo Surround Back
In conventional systems, the difficulty in identifying the sound from the rear channels causes another problem: the rear centre sound is actually heard from near the front centre, causing it to interfere with the dialogue. Yamaha’s solution is to produce the surround back sound in stereo, thus avoiding any mixing of front and surround back channels. The result is clearly defined dialogue and vocals from the front centre channel, clearly distinguishable from the sounds output from the surround back channels.
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Conventional System
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AIR SURROUND
XTREME
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5. Wide Mode
With conventional systems, the area in which the surround effect can be fully experienced is limited to the optimum listening position, called the “sweet spot.” Yamaha increased this area by adding a Wide Mode to the Normal Mode. Selecting Wide Mode will broaden the effective surround area by increasing the number of sweet spots. This mode is especially handy when more than one person is listening. It is capable of providing nearly the same level of realistic sensation over a broader area than the Normal Mode. |
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Normal Mode
creates focal sweet spot.
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Wide Mode
creates multiple
sweet spots.
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6. Well-Defined Centre Channel
Having no centre speaker physically, it has been a real challenge for conventional virtual surround systems to produce clear, centred dialogue and vocals. With this technology, movie dialogue and vocals are actually heard from the centre channel, namely from screen as they should be, and more specifically, from the mouths of people! |
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Conventional System
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AIR SURROUND
XTREME |
7. Optimum Listening Position Adjustment — Position Mode
The Position Mode was developed as a solution for when the listening position cannot be exactly in between the two speakers. It lets you adjust the optimum sweet spot by balancing the distance between the two speakers and the listening position. With this mode, you can sit where you like, and you will be right in the sweet spot! |
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| The Postion Mode lets you set the best listening position |
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