Telephonic communications – Audio message storage – retrieval – or synthesis – Message signal analysis
Reexamination Certificate
1998-09-29
2001-06-26
Weaver, Scott L. (Department: 2645)
Telephonic communications
Audio message storage, retrieval, or synthesis
Message signal analysis
C379S088220
Reexamination Certificate
active
06252945
ABSTRACT:
BACKGROUND OF THE INVENTION
Field of the Invention
The invention relates to methods for recording a digitized audio signal and a telephone answering machine in which such methods can advantageously be employed.
In digital answering machines currently available on the market, the digitized signal of a recorded acoustical message is reduced from the data quantity that recorded with optimal conversion to a lesser data quantity in order to save on the cost of required memory. For storing digital data in memory, the analog speech signal is digitized at a predetermined sampling rate in a first step. The resultant data stream is compressed in a second step with the aid of a data or speech compression process. The data stream reduced by the data compression is then recorded in a third step in a digital memory. A system operating on this principle has been integrated for instance into the answering machine, type GIGASET 1030 available from the present applicant.
The ratio between the incoming data stream per unit of time (that is, the sampling rate of an A/D converter or of the digital speech information arriving in an ISDN telephone) and the data stream per unit of time present after the data compression is called the data compression rate. A high data compression rate accordingly achieves a major reduction in data volume as a result of the compression. However, with an increasing data compression rate the speech intelligibility drops. A compromise must be made between the magnitude of the data compression rate and the resultant speech intelligibility.
In currently available answering machines, the digital speech recording is done with a fixed data compression rate. Some equipment still allows manual variation of the data compression rate, but that must be specified by the user and cannot be controlled automatically. Other equipment allows retroactive data condensation of already recorded messages, in that the recorded messages are read out of the memory and subjected to data compression and then written back into the memory. This process is often called recompression.
A method for controlling signal recording for a digital answering machine is known from Published, Non-Prosecuted German Patent Application DE-OS 44 26 534. In the method, once again, the possibility of data compression is employed.
According to the method disclosed therein, the signal recording is controlled by regulating the ratio between speech quality and recording capacity as a function of the data quantity to be recorded. To that end, the data compression rate is set as a function of the still-available memory capacity, or data recompression is performed. However, then it is always an entire message that is subjected to data compression.
From Japanese Patent Disclosure JP-8-98134, a data recording device has become known in which the digitized video or audio data are recorded in a recording medium at a variable compression rate. The compression rate is made dependent on the data information quantity with the aid of a discriminator circuit. This entails a great expense for circuitry.
SUMMARY OF THE INVENTION
It is accordingly an object of the invention to provide a method for recording a digitized audio signal, and a telephone answering machine which overcome the above-mentioned disadvantages of the prior art methods and devices of this general type, with which the data compression of an audio signal can be manipulated more flexibly, in an especially simple manner.
With the foregoing and other objects in view there is provided, in accordance with the invention, a method for recording a digitized audio signal in a telephone answering machine, which includes: a) writing in a digital input signal during a first time segment resulting in a written data signal; b) compressing the written data signal with a compression algorithm at a predetermined first compression rate greater than or equal to 1 resulting in compressed data; c) storing the compressed data in a storage medium for storing digital data; d) writing in the digital input signal after the first time segment resulting in a further written data signal; e) compressing the further written data signal with the compression algorithm at a predetermined second data compression rate resulting in further compressed data, the second data compression rate being greater than or equal to the first data compression rate; and f) storing the further compressed data in the storage medium.
One preferred method for recording a digitized audio signal according to the invention is performed by writing in the digital input signal up to a first time and storing the written-in data in a storage medium. The writing in of the digital input signal is continued after the first time, and the data then written in are compressed by a compression algorithm, which typically involves loss, in accordance with a predetermined first data compression rate. The compressed data obtained after the data compression are then recorded in the storage medium. Such a procedure is advantageous, since in a telephone call the caller will typically say his name and possibly his telephone number and address at the beginning of the call. This information should be recorded with the highest quality. The part of the message that follows can then be recorded with reduced speech quality, because the caller is identified and any information that might then be lost can as a rule be easily recovered. In a preferred embodiment of the method, the first time period depends on the written-in signal. In an alternative embodiment, the first time period has a predetermined value. In an especially preferred exemplary embodiment of the invention, the input signal written during the first time period is subjected to data compression at a first data compression rate. The first data compression rate is less than or equal to the second data compression rate. The second data compression rate reduces the data quantity in the initial portion of a telephone call to a value at which a predetermined minimum speech quality is assured. Nevertheless, the data quantity to be recorded is reduced compared with the data quantity originally present.
In an especially preferred exemplary embodiment of the invention, before the digital input signal is written in, an already recorded digitized audio signal is read out of the storage medium. That is, a signal to be written in is obtained by readout of a stored message from the memory, so that it can then be resubjected to compression. This brings about recompression of the already recorded data after the first time period, so that by the compression of the data storage space for further recordings is made available. It is especially preferred in this respect that the compression be done at a predetermined third data compression rate, which is greater than the first compression rate. This is especially advantageous when a first data compression has already been performed the first time a recording was made. The first, second and third compression rate are each chosen from many available compression rates.
It is very particularly preferred also that the read-out digitized audio signal be checked for its compressibility. This assures that the speech quality will not be impaired excessively. The checking is preferably done on the basis of the signal of the read-out audio signal, the magnitude of background noise contained in the audio signal, or the fact that the audio signal has already been listened to. It is especially preferred that this recording method be performed successively until the checking shows that no further compression is possible.
In each of the exemplary embodiments described, the first, second and third compression rate should be chosen on the basis of the input signal from the many available compression rates. In this choice, it is also possible to dispense with data compression entirely. It is also especially preferred, when data are stored in the storage medium, that information about the compression rate that has just been used be stored in the storage medium. That information can
Degenhardt Achim
Hermann Michael
Foster Roland G.
Greenberg Laurence A.
Lerner Herbert L.
Siemens Aktiengesellschaft
Stemer Werner H.
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