Headzone - 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 device 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.
Surround On Stereo Headphones - How To Trick Your Brain
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:
a. Head Related Transfer Function (HRTF): Describes various parameters of the sound signals at both ears, via:
a.a. Run time differences: Sound arriving at the listener from the right will be heard first at the righthand ear and will arrive at the left-hand ear a short while later.
a.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.
b. 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.
c. 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 perceived room size of the surrounding room.
d. And finally headtracking: 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!
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”.
The Virtual Control Room
After being able to create “virtual loudspeakers”, the next question will be how to place these loudspeakers in a room, as the actual sound image is composed by the loudspeaker itself and the acoustic characteristics that are added by the room it is standing in. With other words, your “virtual control room”.
For quite a long time the recording industry has been defining the characteristics of a listening control room. These are defined in today’s standards such as: OIRT E86/3, IEC 268-13, N 12-A, EBU 3276-2, ITU-R BS.1116, SMPTE 202M, ISO 2969,THX 1138, etc. The main thing that we learn from of the different standards is that THE perfect control room does not exist, as everyone defines it a little bit differently. But we also learn what the qualities of a good reference listening room are, namely:
- Reverberation time 250 – 400 ms
- Defined room geometry
- Low background noise level
- No strong reflections that alter the sound colour
- Highly diffuse reverberation tail
When modelling a virtual control room for the Headzone system, we could have measured out some “legendary” control rooms and put them into Headzone, but what would the benefit be for you if you were able to work in the virtual “Abbey Road Studios”? You have probably never worked there and perhaps never will in your lifetime… and even if you did… perhaps you would not like the sound of the control room at all.
For the “Headzone Virtual Control Room” we decided to take a different approach: If THE perfect control room doesn’t exist, but we know the qualities of a good reference listening room... why not allow you to adjust the listening room and create your OWN perfect control room? In our opinion a good sounding control room is quite a personal thing and therefore flexible within certain limits. It is perfect when you feel at home and comfortable with the room response and the distance perception. In other words, when the room sounds plausible to you.
Most importantly, you should always be able to use the same listening conditions, even outside your studio, while recording, or during listening sessions while travelling. This gives you all the benefits of a true reference listening room, where a sound engineer can easily judge the quality of a recording. The more you work in that specific room, the easier you will be able to tell how this would sound in any other environment. In addition, with Headzone, you are only a few mouse clicks away from listening to your production in different environments to double check that what you have mixed for “living-room” conditions will also sound right in a small car!
The Headzone virtual control room is therefore based on the qualities of a good reference listening room as described above, but Headzone also allows the user to custom-design the sound characteristics of a loudspeaker system in a control room with just a few mouse clicks. Adjustable parameters include all those effects that additionally affect the sound image in a real room and that are omitted in conventional stereo headphones: the size of the room, the distance of the loudspeaker to the listener and the characteristics of the control room.
We deliberately incorporated all parameters into just 3 sliders (Room Size, Distance and Ambience), which are easy to understand and operate within a range of 0 to 100. In fact, when adjusting your personal control room, we want to encourage you to do what you can do best: use your ears! Just start playing around with the room parameters in your virtual control room. As soon as you feel that your setting sounds realistic and convenient, you’ve made it! You’ve created your own reference control room, which you can now take with you anywhere in the world.
Loudspeakers do not move!
Loudspeakers are installed at fixed positions within a room and provide a sound impression that is spatially stable. The loudspeaker does not change its position with the listeners’ every movement, but will sometimes be in front of them, next to them or behind them, depending on their movements/position. In contrast, headphones are attached to the user’s head, which means that a signal coming from the right-hand earpiece of the headphones will always remain to the right of the user because the headphones also turn when the listener turns his head. Since we are not used to „moving loudspeakers“, our brain is constantly reminded of the fact that we are just wearing headphones.
Headzone solves this problem with the development of new, patented technology. With the help of an ultrasonic headtracker, the system continuously tracks the head position of the listener and adjusts audio reproduction accordingly. For example, if the user places a virtual loudspeaker in the front right-hand corner of the room, it will always remain in that position. The user can turn towards or away from the loudspeaker… no matter how he moves, the loudspeaker does not move and remains at the same virtual location. This allows for a striking degree of reality in surround reproduction, which could not be achieved until now, as at a certain point the brain forgets that the person is wearing headphones. You feel as though your virtual listening control room is real, but even better, as you can easily take it with you.
As already mentioned above, we unconsciously turn our heads in order to localise a sound source. During this movement, headphones without headtracker will, of course, also turn the sound image by the same degree, whilst headphones with headtracker ensure that the brain will once again receive the additionally required space information – just as in real life.