Professional quality processor
Universal interfacing
Digital signal processing
Digital signal transmission
using ACS Audio Coding
System
Digital receiver
Acoustic status indicator
UHF headphones available
separately
2.5 IVA Individual Virtual
Acoustics
The HEARO 888 DIGITAL is a UHF transmitter designed specifically for use with HEARO DIGITAL wire-
less headphones from AKG. Outputs for hardwire stereo headphones and loudspeakers allow the unit to
be used in professional recording studios as well. The heart of the HEARO 888 DIGITAL is a high quality
digital signal processor whose high resolution ensures optimum sonic results with both analog and digi-
tal program material.
The HEARO 888 DIGITAL provides analog and a coaxial digital input for easy interfacing with analog out-
puts on audio, video, TV equipment or PCs as well as coaxial digital outputs on DVD and CD players or
digital TV sets.
Analog signals are digitized immediately after the input stage. All signal processing that affects the sound
takes place in the digital domain. This maintains the full dynamic range of the input signal and minimizes
noise. Digital signals remain in the digital domain from the source to the headphones to ensure the high-
est possible audio quality.
The signal is transmitted in its digital form to the receiver in the wireless headphones. Conventional dig-
ital audio signal transmission techniques delay the signal by about 60 to 100 milliseconds due to the
required data processing. As a result, TV or video sound may seem slightly out of sync. The ACS Audio
Coding System developed by AKG is he first technique that reduces the time delay to approximately 5
milliseconds so that there will be no noticeable delay between picture and sound.
The receiver built into the headphones converts the received digital signal into an analog audio signal.
The greatest advantage of digital over analog transmission is that it requires neither an automatic gain
control (AGC) nor a compander system. This maintains the full original dynamic range of the audio sig-
nal. Other benefits of this process include minimum noise, better high-frequency reproduction, lower dis-
tortion, better interference rejection, and consistent transmission quality throughout the transmitter range
of up to 165 feet (50 m) under ideal transmission conditions (free field). Unlike infrared signals, RF signals
will penetrate walls and ceilings.
Reflections of the transmitter signal off metal objects etc. may weaken or even cancel the transmitter sig-
nal in some places (so-called "dead spots"). In many cases, all it takes to restore clear reception is to
move a few inches to one side. The receiver in the HEARO DIGITAL uses two antennas integrated in the
arches to receive the transmitter signal at two different points in space. The diversity circuit will auto-
matically activate the antenna that delivers the better signal at any time. This system reduces the num-
ber of dead spots considerably and dramatically improves reliability of reception.
If the transmitter and receiver are tuned to different frequencies or if you are too far from the transmitter,
you will hear a beep in the headphones.
The HEARO 888 DIGITAL system lets you share your listening enjoyment with other persons. You can
operate your transmitter with several digital headphones simultaneously. Make sure to use digital wire-
less headphones operating in the same UHF frequency band as the HEARO 888 DIGITAL.
One drawback of headphone listening is the psychoacoustic phenomenon of "inside localization": the
orchestra seems to play inside your head rather than in the room. AKG developed a binaural audio pro-
cessing technique called IVA (Individual Virtual Acoustics) that models the way the head and pinnae
change the arriving sound waves (ear matching function). Thus, the various sound sources will seem to
be located outside your head even when you are using headphones.
A:
Natural hearing: Due to the effect of the head and pinnae, sound
waves arriving at one ear differ from those arriving at the other.
Amplitude and phase differences create a sense of spatial hearing.
B:
Listening through headphones: Amplitude and phase differences
are eliminated. Sound sources are localized inside the head rather
than in the room.
C:
Listening through headphones with IVA processing: The ear
matching function modifies the audio signals at the ears to resemble
diagram A. This restores natural, spatial hearing.
2 Description
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