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HRTF FIR
 

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Real-time 3D sound playback system (RT3D)

(1) Perception of Sound Arrival Direction
(2) 3D Playback with Headphones
(3) 3D Playback with Speakers

Features

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Real-time convolution with HRTF (Head-Related Transfer Function)
HRTFs on every 5-degree are convolved in time-domain.  Because HRTFs in all the angles are always being convolved, a virtual sound source is swung smoothly by mouse.
Producing a three-dimensional sound field by Binaural technology.

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Free angle localization
Sound sources are set on every 5-degree angle, and various sound alignments can be tried.

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Comes with a design tool for a cross-talk canceller.
A cross-talk canceller is necessary to cancel cross-talk for trans-aural systems. This software comes with an "Impulse response measuring tool", and an "Inverse filter design tool", which is used for designing a cross-talk canceller.

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Software name : RT3D (Real-Time 3-Dimension)
 

boards

RS-CP561RS-USB1

Input & output I/F

AES/EBU, Optical TOSLINK

Sampling Frequency

48kHz (Synchronize with an input source)

HRTF convolution

max. 512 taps for each 72 pair

Cross-talk canceller

4096 taps FIR

HRTF file format

WAV file format

 

(1) Perception of Sound Arrival Directions

 How does a person sense a direction of sound ?

 A person uses both right and left ears to listen to the sound. Simply he or she might find out that it is from the right direction if the sound reaching the right ear is louder than the left ear. Or, if the sound reaching the right ear is preceding the left ear, they feel it is also from the right direction. Therefore, if sound levels at the right and left ears (the difference is called  Internal Level Difference: ILD) or sound arrival times (the difference is called Internal Time Difference: ITD) can be changed artificially, the sound source position can be located anywhere you like.

Sound level differs    Arrival time differs

 Although, only by changing ILD and ITD, they cannot recognize forward and backward direction, or upward and downward direction. Because the sound source is at the line symmetric position and the ILDs and ITDs are equal. How complicated our ears are! 

(2) 3D Playback with Headphones

 HRTF (Head-Related Transfer Function) shows characteristic from a sound source at various angles and height to an ear, and it is paired with one HRTF for the right ear and another HRTF for the left ear. HRTF contains ILD and ITD information as well. Furthermore, it contains characteristics of our head and ears' shape, so we can recognize a direction even at a line symmetric position. Convolve any sound you like with some HRTF and listen to the convolved sound with headphones, the sound seems to come with some angles and height virtually. The sound convolved with HRTF of some angles (called Binaural Recording Sound) can be heard arriving from the specific direction of HRTF.
 Redec software "RT3D" convolves an input sound with HRTFs on every 5-degree angle and plays it in real time.

(3) 3D Playback with Speakers

 In the case of using stereo speakers to play a binaural sound source, the space between speakers and ears becomes a problem. While playing, unlike with headphones, the sound from the right side speaker would reach the left ear not only the right ear, and vice versa. This is called "cross-talk". In addition, the sound from the speakers would be distorted through the air space. It turns out that this method does not work out.

It is a cross-talk canceller to vanish the cross-talk and the space characteristic which distort the sound.
 Redec "RT3D" comes with this cross-talk canceller, and makes it possible to play binaural sound sources without headphones.

 

 

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Last update : 2010/06/19