Patent
1995-01-03
1997-08-19
MacDonald, Allen R.
395 21, 395 214, 395 222, 395 221, G10L 900
Patent
active
056596600
DESCRIPTION:
BRIEF SUMMARY
BACKGROUND OF THE INVENTION
1. Field of the Invention
The invention relates to a method of transmitting and/or storing digitized, data-reduced audio signals. Such a method is known, for instance, from the European patent specification 290 581.
2. Description of the Related Art
In a bit rate-reduced encoding of audio signals that are already available in a digitized form, e.g., having a 48 kHz scanning frequency/16 bit resolution, utilization of psychoacoustic phenomena in the perception of audio signals is known from EP 290 581 in a way that the original bit rate is considerably reduced. Such methods carrying out transcoding from a higher to a lower bit rate are commonly known as source coding. They particularly utilize masking effects of the ear in the frequency and time domain. It is the object of these methods to not change, if possible, the audible quality which the audio signal has before transcoding (source coding) by reducing the bit rate (optimum transcoding).
In many applications, there is a limited data capacity available for transmission or storage. If this bit rate, which is made available, is insufficient, a further data reduction according to the principles of optimum transcoding leads to sometimes considerable interference, especially in the form of considerable sound distortions. This same interference, of course, also occurs if the source coding is not two-staged, but takes place in one step.
Furthermore, in a method of transmitting and/or storing digitized, data-reduced audio signals it is known (DE 36 29 434 Al) to let further encoding steps follow if, after encoding, a predetermined bit rate is exceeded (code overload), until the actual bit rate no longer exceeds the designated bit rate. That is, if code overload exists after a first encoding sep, further encoding steps can be employed. However, this approach does not always avoid a code overload with certainty.
SUMMARY OF THE INVENTION
In contrast, it is the object of the present invention to minimize the interference or distortion effect during a further data reduction of an already data-reduced audio signal or during a first data reduction of an audio signal, while accepting code violations.
This object is provided by the present invention so that in the event of a code overload, before the audio signal is encoded, the time behavior and/or the spectral distribution of the audio signal is changed according to a selected adaptation pattern without a considerable signal deterioration being subjectively perceivable after decoding the encoded audio signal.
Advantageous modifications of the solutions according to the invention are described as follows.
BRIEF DESCRIPTION OF THE DRAWING
By way of an embodiment, the invention is explained in greater detail in the only drawing. It shows:
FIG. 1 is a block diagram of an encoder for the implementation of the method according to the invention.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
In the encoder shown in FIG. 1, the arriving analog audio signal 11 is fed to an analog/digital conversion stage 10. The analog signal 11 has various signal features, such as a spectral distribution and a time behavior (or behavior during the course of time). The digitized audio signal 12 is fed to a stage 40, to be explained later, for signal analysis, to a signal change stage 20, as well as to delay elements 15 and 70. In the signal change stage 20, the digitized audio signal is processed as a function of a change recommendation 41 generated by the signal analysis stage 40. The change recommendation 41 may also be to not change anything. The processed and possibly changed audio signal 21 at the output of stage 20 is reduced in a subsequent data reduction stage 30 with regard to the data rate available for transmission or storage. This data reduction is carried out as a function of an encoding recommendation 42 which is made available by the signal analysis stage 40. The encoded audio signal 31 at the output of stage 30 is fed to a data expansion stage 50 for use in a recursive control process, wh
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Link Martin
Plenge George
Wiese Detlef
Chawan Vijay B.
Institut Fuer Rundfunktechnik GmbH
MacDonald Allen R.
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