Speech compression and tone detection in a real-time system
Abstract: During the night, encrypted spoken newspapers are broadcasted over the
terrestrial FM radio network. These papers can be subscribed to by
persons with reading disabilities. The subscribers presently have a
special receiver that decrypts and stores the newspaper on a cassette
tape. A project aiming to design a new receiver, using digital
technology, was started during the year 2002. This report describes
the parts of the project involving speech compression and tone
detection. An overview of different compression techniques, with
emphasis on waveform coding, is given. A detailed description of
Adaptive Differential Pulse Code Modulation (ADPCM), the compression
technique chosen for implementation on a Digital Signal Processor
(DSP) is also included. ADPCM was first implemented on the ADSP-2181
DSP, with a good result. In the final version of the digital receiver
the ADSP-2191 DSP will be used and hence the code was converted to fit
this DSP. Due to some problems this implementation could not be
completed within the time frame of this thesis.
The final part of this thesis consists of finding a method for
detecting a tone inserted between articles in the spoken
newspaper. The tone detection is composed of two parts, the first part
is reducing the amplitude of the speech while maintaining the
amplitude of the tone. For this part a digital resonator was chosen
and implemented both in Matlab and on the ADSP-2191 DSP. The second
part of the tone detection consists of deciding whether the tone is
present or not, this part was implemented only in Matlab.
CLICK HERE TO DOWNLOAD THE WHOLE ESSAY. (in PDF format)