Music – Instruments – Electrical musical tone generation
Reexamination Certificate
2000-02-22
2001-03-13
Witkowski, Stanley J. (Department: 2837)
Music
Instruments
Electrical musical tone generation
C708S203000, C708S420000
Reexamination Certificate
active
06201175
ABSTRACT:
CROSS-REFERENCE TO RELATED APPLICATIONS
Embodiments of the present invention relate to and claim priority to Japanese Patent Application No. 11-254569, filed on Sep. 8, 1999, and the contents of that application are incorporated by reference herein.
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a waveform reproduction apparatus with which a waveform that has been compressed or expanded in the direction of the temporal axis is reproduced.
2. Description of the Related Art
For some time, waveform reproduction apparatuses with which a waveform that has been compressed or expanded in the direction of the temporal axis is reproduced have been known. For these waveform reproduction apparatuses, a number of formats have been proposed. Here an explanation will be given first regarding a waveform reproduction apparatus that uses a cross-fade format.
FIG. 12
is an explanatory diagram of a cross-fade format in which a musical tone is compressed or expanded in the direction of the temporal axis.
In the waveform reproduction apparatus that uses the cross-fade format, the waveform data that express the waveform of the musical tone are stored in a RAM that is not shown in the diagram. The waveform data that have been stored in the RAM are read out and, as is shown in FIG.
12
(
a
), the waveform data in a specified segment (known as the “opened segment”) are jump read and the waveform is compressed or, as is shown in FIG.
12
(
b
), the waveform data in a specified segment (known as the “repeated segment”) are repeated and read out and the waveform is expanded. By means of carrying out this action, it is possible to restrain the changes in the pitch with a waveform that has been compressed or expanded and to preserve the pitch of the musical tone. In addition, with the cross-fade format, since noise that is generated in the vicinity of the discontinuous areas of the links between a particular segment and the segments that adjoin that segment is suppressed, it is possible to carry out cross-fade processing in the vicinity of the discontinuous areas.
Here, the meaning of cross-fade processing is processing in which, by means of gradually increasing the amplitude of a waveform that has begun to be read out anew (this is made the later waveform) together with the gradual reduction of the amplitude of the waveform that has been read out up to that point (this is made the head waveform), a transition is made smoothly from the head waveform to the later waveform.
However, with this cross-fade format, since the waveforms that represent musical tone waveforms that are continuous are jump read out or repetitively read out directly, even though cross-fade processing is carried out, there is a problem in that fluctuations or ripples are produced in the waveform that has been compressed or expanded due to such things as a shift in the phase.
In order to solve this problem, a waveform reproduction apparatus called a phase vocoder has been presented. Below, an explanation will be given in regular sequence regarding this phase vocoder.
With the phase vocoder, the original waveform, which expresses the original musical tone prior to carrying out compression or expansion is input. The phase vocoder divides the original waveform that has been input into a multiple number of frequency bands.
FIG. 13
is a diagram that shows the multiple number of frequency bands that have been divided by a phase vocoder.
The original waveform that has been input is divided into a multiple number (here, there are 100) of frequency bands (band
0
,
1
, . . . k, . . . , p, . . . ,
99
) which have the center frequencies &ohgr;
0
, &ohgr;
1
, . . . , &ohgr;k, . . . , &ohgr;p, . . . , &ohgr;
99
that are respectively the integer multiple frequencies that represent the fundamental frequency and the harmonics of the fundamental frequency including the second harmonic, third harmonic etc. In addition, this phase vocoder, for each waveform component of the respective multiple number of frequency bands that have been divided, extracts the frequency data and the amplitude data of each of the waveform components that represent the frequencies that change in order together with the passage of time (known as the instantaneous frequency) and the amplitudes that change in order together with the passage of time. The frequency data and the amplitude data that have been extracted in this manner are stored in the memory.
At the time of the reproduction of the waveform, the temporal change rates are adjusted for the frequencies and amplitudes that are expressed by the frequency data and the amplitude data that have been extracted in each frequency band.
FIG. 14
is a schematic diagram that shows the aspects of the frequency and amplitude temporal change rates that have been adjusted by the phase vocoder.
In FIG.
14
(
a
), the amplitude envelope and the frequency envelope that are expressed by the amplitude data and the frequency data that change together with the passage of time in a certain single frequency band are shown. As is shown in FIG.
14
(
b
), the amplitude data and the frequency data are corrected by the adjustment of the temporal change rate for the frequency and the amplitude in accordance with the degree to which expansion or compression are carried out and the envelope is expanded or, as is shown in FIG.
14
(
c
), the amplitude data and the frequency data are culled out and the compression of the envelopes is carried out. By doing it in this manner, after the amplitude envelopes and the frequency envelopes have been adjusted for each frequency band, the cosine waves that have been finely adjusted by an oscillator with which the fine adjustment of the frequency is possible in accordance with the frequency envelope for the center frequency of each of the frequency bands together with the passage of time are obtained. The amplitudes of the cosine waves are finely adjusted in accordance with the amplitude envelopes together with the passage of time and, in addition, in this phase vocoder, all of these waveforms that have been reproduced are combined. In this manner, a reproduced waveform in which the original waveform that has been input has been compressed or expanded in the direction of the temporal axis is obtained.
Since the phase vocoder that has been discussed above is one in which the original waveform is divided into a multiple number of frequency bands, the temporal change rates of the frequencies and the amplitudes that change together with the passage of time are adjusted for each of multiple number of frequency bands that have been divided and, by means of the reproduction of the time conversions for the frequencies and the amplitudes following adjustment, a reproduced waveform in which the original waveform has been compressed or expanded in the direction of the temporal axis is obtained, compared to the case, as in the waveform reproduction apparatus that uses the cross-fade format, in which the waveform data that express the original waveform are themselves directly jump read out or repetitively read out, noise and fluctuations due to such things as a shift in the phase are reduced.
However, in this phase vocoder, with such things as voices and brass where the period of the waveform is long or the waveforms of chords, if the expansion and compression rate, which represents the proportion of compression or expansion, is varied greatly from 1.0 for both compression and expansion, there is a breakdown of the harmonic relationships of the musical tones that are expressed by the waveforms that have been compressed or expanded in the direction of the temporal axis. A detailed explanation of this phenomenon will be given below.
In the case of the phase vocoder discussed above, in order to provide a theoretical description, it was explained to the effect that the original waveform that has been input is, as is shown in
FIG. 12
, divided into a frequency band that contains the fundamental frequency, a frequency band that contains only a frequency that is twice the fundamental frequen
Hoshiai Atsushi
Kikumoto Tadao
Kusakabe Satoshi
Foley & Lardner
Roland Corporation
Witkowski Stanley J.
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