Sennheiser DSP PRO Instructions For Use Manual page 25

2) A sound arrives at your ears with a different volume (level difference).
Let's use the door example again. The right ear receives the sound signal directly,
whereas the left ear is turned away from the sound source. You will hear the sound
louder with your right ear. The shape of the outer ear (pinna) and the attenuating effect
of the head, hair, clothes etc. help the brain to determine the direction of the sound. The
attenuation is also dependent on frequency. Higher frequencies are attenuated to a
greater degree (approx. 30 dB at 15 kHz) than lower frequencies (approx. 5 dB at 50 Hz).
Thus, it is important for the localisation of a sound source to use good headphones which
optimally reproduce the treble, such as Sennheiser headphones.
DSPpro creates a virtual room
The Toltec processor in DSPpro computes the time delays and level differences for the
position of each loudspeaker in a Dolby Surround system. Thus, it produces five pieces of
directional information for each ear, a total of ten "head-related transfer functions". When
a sound signal is processed using this directional information – this process is called filtering
– you will get the impression of listening to real 3D sound with your headphones. A virtual,
three-dimensional world of sound is created!
HRTF (Head-Related Transfer Functions)
More than 20 years ago, Sennheiser was the pioneer of "head-related stereophony" and
dummy head technology. Since then, Sennheiser has pursued the idea of head-related
recording systems. HRTF systems have now opened the door to Surround sound via
standard stereo headphones. Sennheiser is co-operating with renowned research laboratories
worldwide specialising in the development of HRTF systems.
HRTF signals are obtained by placing tiny microphones into the ears and recording the
acoustic characteristics of the head and pinna for all directions of incidence around a
listener. Precise HRTF measurements are essential for an authentic 3D sound system.
For DSPpro, about 600 HRTF measurements of different human ears have been analysed.
Of these, 15 representative, typical ear types have been selected and programmed in
DSPpro. At least one of these ear types will come very close to matching your own ears and
thus enable you to enjoy a true 3D sound experience.
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