Data processing: speech signal processing – linguistics – language – Audio signal time compression or expansion
Reexamination Certificate
2000-11-29
2004-08-31
Dorvil, Richemond (Department: 2654)
Data processing: speech signal processing, linguistics, language
Audio signal time compression or expansion
C704S500000, C381S107000, C455S560000
Reexamination Certificate
active
06785657
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to a digital signal processor which performs output switching between plural digital audio data and, more particularly, to a digital signal processor employed in a device such as a DVD player or a digital broadcast tuner, which performs output switching between audio data and coded audio data obtained by compressing audio data.
BACKGROUND OF THE INVENTION
With recent developments in multimedia technology, various devices for handling multiple media such as digitized video, audio and data integrally, typified by a DVD player and a set top box for receiving digital TV broadcasts, are becoming widespread.
These devices employ a digital audio interface, popularly called IEC958, for transmitting digital audio data to peripheral devices. This digital audio interface is used not only for transmission of audio data but also for device-to-device transmission of stream data which is compressively encoded according to a standard such as MPEG, DolbyAC-3, DTS, or the like. A DVD player or a digital TV tuner is required to switch the data to be transmitted through the digital audio interface, i.e., to switch its output between the audio data and the stream data.
For example, the DVD player performs output switching between audio data and stream data when there is an instruction from the viewer to switch the audio output from audio data to MPEG stream data of the same content.
Further, in the case where two kinds of digital audio data, such as MPEG stream data (first audio) and audio data coded by linear PCM (second audio), are recorded on the same track of a DVD video disk, the DVD player performs output switching when receiving an instruction from the viewer to switch the output from the first audio to the second audio. To be specific, this corresponds to the situation where the DVD player receives an instruction to switch the data of Japanese as the first audio to the data of another language as the second audio, from the viewer who can watch the DVD video with a variety of languages.
As another example, when the digital TV tuner performs channel switching to select a digital broadcast station, the tuner may switch its output between audio data and stream data.
Hereinafter, a description will be given of a digital signal processor performing output switching between audio data and stream data in a DVD player or a digital TV tuner, with reference to
FIGS. 3
to
5
.
FIG. 3
is a block diagram illustrating the structure of a conventional digital signal processor.
In
FIG. 3
, reference numeral
101
denotes a first signal generator which generates stream data
105
according to a standard such as MPEG, DolbyAC-3, DTS, or the like, and transmits the stream data
105
serially; numeral
102
denotes a second signal generator which generates audio data
106
, and transmits the audio data
106
serially; numeral
103
denotes a signal switching unit which outputs either the stream data
105
supplied from the first signal generator
101
or the audio data
106
supplied from the second signal generator
102
, and switches the output; and numeral
104
denotes a signal switching controller which receives an instruction from the viewer to switch the audio output (hereinafter referred to as “switching instruction”), and outputs an instruction signal
107
for switching (hereinafter, referred to as “switching instruction signal”).
FIG. 4
is a diagram illustrating a format of stream data generated according to the MPEG standard or the like.
With reference to
FIG. 4
, stream data
105
generated by the first signal generator
101
comprises a plurality of successive frames. A sync preamble, in which the type of data, the length of data, etc. are described, is placed at the beginning of each frame, and this sync preamble is used for frame identification or the like by a decoder.
FIG. 5
shows the time charts of the respective signals outputted from the conventional digital signal processor when the processor receives an audio switching instruction from the viewer while a DVD player or the like is playing a disk. In
FIG. 5
, the same reference numerals as those shown in
FIG. 3
denote the same or corresponding parts.
In
FIG. 5
, T3 denotes a point of time at a boundary of periods of the stream data
105
(i.e., a boundary of two frames), and “last a” is the last data in a frame while “head b” is the first data in the next frame. Further, the second signal generator
102
does not generate audio data
106
during a no-signal output period B, and it starts to generate “head c” as the head data of the audio data
106
at time T4.
Hereinafter, the operation of the conventional digital signal processor will be described using
FIGS. 3 and 5
.
At time T1, the first signal generator
101
generates stream data
105
and outputs it. The signal switching unit
103
is connected to the first signal generator
101
, and outputs the stream data
105
supplied from the first signal generator
101
. At this point of time, the second signal generator
102
has not yet started generation of audio data
106
.
When there is a switching instruction from the viewer at time T2, the signal switching controller
104
outputs a switching instruction signal
107
. According to the switching instruction signal
107
from the signal switching controller
104
, the signal switching unit
103
switches the connection from the first signal generator
101
to the second signal generator
102
. However, since the second signal generator
102
has not yet started generation of audio data
106
at this point of time, the signal
108
outputted from the signal switching unit
103
is invalid data.
At time T4, the second signal generator
102
starts to generate audio data
106
and, simultaneously, “head c” of the audio data
106
is output from the signal switching unit
103
.
As described above, when there is a switching instruction from the viewer at some point in a period of the stream data
105
outputted from the signal switching unit
103
, the output of signal switch unit
103
is immediately switched from the output of the first signal generator
101
to the output of the second signal generator
102
and, consequently, the latter part of the frame in the stream data
105
including “last a” is not output from the signal switching unit
103
, resulting in a lag time A due to the switching.
Further, during the period from when the output of the signal switching unit
103
is switched from the output of the first signal generator
101
to the output of the second signal generator
102
to when the second signal generator
102
starts to generate audio data
106
, the output signal
108
from the signal switching unit
103
is invalid data, and a time lag occurs during this period.
As described above, when the conventional digital signal processor receives an audio switching instruction from the viewer while the DVD player is playing the disk, the signal processor switches its output to the audio data during a period of the stream data and, furthermore, it outputs the stream data from some point in the period when switching the audio data to the stream data.
Therefore, when a digital AV amplifier with a built-in decoder (not shown) as a peripheral device of the DVD player receives a frame which lacks a part of the sync preamble, the digital AV amplifier continues to reproduce the stream data as audio data until it detects the sync preamble of the next frame, and this causes noise.
Furthermore, if the output level of the audio data is high when switching the output between the audio data and the stream data, a shock sound occurs. Further, if generation of data to be output after the output switching is not started yet by the time of the output switching, a pause occurs between the played audio data, and the audio is interrupted for a moment. Thus, the noise generated at the audio switching grates on the viewer's ear, and makes the user uncomfortable.
In order to prevent such malfunction of the decoder and occurrence of noise and shock sound at the audio output switchi
Dorvil Richemond
Harper V. Paul
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