Patent DE-2203921-C3 (DE)
IPC: G10L19/02
Filed: 1972-01-28
Granted: 1979-09-20
Abstract: 1345828 Speech synthesis INTERNATIONAL BUSINESS MACHINES CORP 21 Jan 1972 [2 Feb 1971] 2908/72 Heading H4R In a speech synthesis equipment a "given sound", e.g. a period of sound lasting 25 m.s., is produced by generating samples of the "given sound", the samples for example being produced at 100 Á.s. intervals, and reproducing the samples in sequence to yield the "given sound", the arrangement being characterized in that each sample of a "given sound" comprises a combination of the time, and therefore sample, dependent amplitude values of a fundamental frequency and its harmonics weighted by the fourier coefficients of the fourier series representing the "given sound", each successive sample of a "given voiced sound" being produced using the same fundamental frequency, whereas each sample of a "given unvoiced sound" is produced using a fundamental frequency which differs randomly from the fundamental frequency of the previous sample. Detailed Arrangement.-Each "given sound" to be generated can be represented by a fourier series and to produce a range of different "given sounds" 20 fundamental frequencies are used, which are each stored as a series of digital values representing amplitude values of the frequency at successive times corresponding to successive samples. i.e. each frequency is given a main address B. The first digital amplitude value is given an address B+#, the 2nd an address B + 20 and so on until at an address B+n# the digital values start being repeated. To generate the 2nd harmonic an address B + 20 is used for the first digital amplivalue followed by addresses B+2n# for successive values. Similarly for the 3rd harmonic addresses B + 3n# are used. Fig. 2 shows an arrangement for achieving the synthesis of a "given sound", LS is a local store which receives over the line CHANNEL INPUT data indicative of whether a sound is voiced or unvoiced, the values of B and # and the fourier coefficients An. In read only memory SIN are stored the fundamental frequencies, each being a series of digital values stored in a main address B as described above, a random number generator GBA is provided for supplying values of B when generating samples of unvoiced "given sounds". In operation a value of B is transferred through ADD 1 to REG 1 from store LS in the case of a voiced "given sound" or from random number generator GBA in the case of an unvoiced "given sound". From REG 1 it is returned as input to ADD 1 together with # from LS and # and B are added to provide the address of the first sample of the fundamental frequency. This address is fed to REG 1 from which it is fed to store SIN to cause the read out of the digital value stored at address B + # and to LS to cause read out of A1. In ADD/MULT the fourier coefficient A 1  is multiplied by the contents of B+# and the product is stored in REG 2. The address B + # is also fed back to ADD 1 where 0 is again added to give the address of the digital value of the second harmonic. This new address is fed to REG 1 causing A 2  and the contents of B + 2# to be read to ADD/MULT. The product is obtained and is added to the previously obtained product stored in REG 2. The process is then repeated for between 50-100 harmonics. The sum of the products stored in ADD/MULT represents a sample of the "given sound". This sample is then fed to a digital to analogue converter D/A and is then outputed. Synthesis of the second sample is then commenced. In the case of an "unvoiced given sound" a different value of B, e.g. different fundamental frequency is used, but for a "given voiced sound" the same value of B is used but addresses B + 2#, B + 4#, &c., will be used. The production of samples continues for 25 m.s. after which time new data is supplied to store LS and the synthesis of samples for a new "given sound" is commenced. Instead of the store SIN containing digital representations of a plurality of different fundamental frequencies only a single frequency may be stored which is represented by digital values taken at a high sampling rate. If the rate is sufficiently high, all the required fundamental frequencies are provided by harmonics of the single stored frequency.