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4. The Headzone technology
4.1 The idea
Headzone emerged from the idea of remodelling the effective parameters of an ideal auditory space with a certain loudspeaker
set-up (up to 5.1) as convincingly and exactly as possible and to make this available in a compact and lightweight transportable de-
vice like an external sound card.
With the help of the lastest DSP-enabled signal processing, Headzone processes the audio channels in such a way that they are
heard in the headphones exactly as they would in an actual room: outside the head, in fixed positions and with a realistic sound
impression.
In contrast to other surround simulations using headphones, which produce an impressive but very diffuse “spatial effect” due to
stereoscopic image widening and reverberation effects, Headzone performs just like a real 5.1 loudspeaker system in a high-quality
control room. Each surround channel is reproduced as a separate, virtual loudspeaker and can be positioned exactly as required by
the user. Headzone places key emphasis on the maximum accuracy of reproduction.
4.3 Virtual loudspeakers
For example, if a mono audio signal is reproduced via a loudspeaker at a distance of 3 m and an angle of 30° to the left of the
listener, this signal reaches the listener with the characteristics specific to each of the two ears (frequency response, run time, space
component etc.). The brain evaluates this information and thereby determines the position of the loudspeaker. Headzone imprints
this information on the audio signal using digital signal processing and can thereby generate the same spatial impression with the
headphones. This makes it possible to position an audio signal virtually anywhere in the space around the listener and thus generate
a “virtual loudspeaker”.
4.2 Surround on stereo headphones… how to trick your brain
The Binaural Environment Modelling® technology, which is the heart of Headzone, basically works on the principle that your
perception is what you hear… and if you hear nothing else than the signals played through two speakers close to your head, i.e.
headphones… why shouldn’t it be possible to generate any perception you like?
In fact, humans always hear in stereo – using the left ear and the right ear. The fact that with two ears we can also hear spatially is
due to the ability of our brain to evaluate the available signals in relationship to each other. This not only creates the left/right
information but also a genuine 3D effect. The actual processes are too complex to describe in a few sentences, but we would like to
mention a few, but critical factors:
1. Head Related Transfer Function (HRTF): describes various parameters of the sound signals at both ears, via:
a. Run time differences: sound arriving at the listener from the right will be heard first at the right-hand ear and will arrive at the
left-hand ear a short while later.
b. Differences in level: sound arriving first at the right-hand ear will travel around the human head and then be heard at the
left-hand ear with an attenuated level and a different frequency spectrum.
2. Relationship between direct sound and diffuse sound: a sound source close by will have a higher proportion of direct sound than
a distant sound source.
3. Typical patterns of early reflections in a room: a sound source that is very close typically generates different reflection patterns
(speed and angle of the reflection incidence) compared to one that is far away. Interestingly, for a human listener, some of these
reflections are used to define the apparent sound source distance, while others will have a more prominent effect on the percei-
ved room size of the surrounding room.
4. And finally head tracking: in a natural environment humans unconsciously use the ability to turn their head in order to find out
exactly where a sound source is located. These are just minute head movements, which nevertheless are extremely important for
natural hearing. It is due to these head movements that we are able to distinguish clearly between front and back (particularly in
spatial hearing). With Headzone, this natural hearing has also been realised in the headphones, since Headzone constantly tracks
the head movements of the listener and incorporates them in the audio reproduction.
If we can succeed in replicating all these factors through digital signal processing (which we do), we can model any required room
information that the human brain perceives as realistic. In other words: we can trick the brain!