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7.1.1 Data compression
With this, digital radio takes advantage of the properties of human hearing. The human
ear does not perceive sounds which are found under a specific minimum volume. Data
which are found under the so-called audibility threshold can, therefore, be filtered
out. This is possible because, in a digital data stream, the relevant relative volume for
other units is saved for every unit of information. Moreover, in an audio signal, the
quieter parts are superimposed by louder ones at a specific limit value. All the sound
information below the threshold of hearing in a piece of music can be filtered out of
the signal to be broadcast. This leads to a reduction of data in the data stream to be
transmied, with no perceptible dierence in sound for the listener (HE AAC v2 process
as a supplementary codification process for DAB+).
7.1.2 Audio stream
With digital radio, audio streams are continuous data streams which contain the MPEG 1
audio layer 2 frames and thereby represent acoustic information. This enables standard
radio channels to be broadcast and listened to on the receiver side. Digital radio
provides you not only with excellent sound quality radio but also additional information.
This may refer to the programme being broadcast or be independent information (e.g.
news, weather, trac, tips).
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