| 摘要 |
PURPOSE:To reduce the scale of the device having a high-quality sound and variety and privacy of key selection, by subjecting the sound signal to high-speed Fourier conversion or high-speed Hadamard conversion to exchange the spectrum, in the secret speech system due to spectrum exchange. CONSTITUTION:If contents of counter 13 indicating the exchange key number are set to ''10'' and the key of decimal indication 2 is set when the same bit pattern ''10'' as counter 13 is set to upper two bits of counter 14 and lower three bits are reset to ''000'', value 5 ''101'' read out from ROM11 becomes the address of RAM10 where the output from high-speed Fourier conversion (FFT) circuit 2 is stored, and lower bits of counter 14 are addressed and written into RAM12. At the next timing, ''1'' is added to content of counter 14, and they become ''10001''. After the same operation is repeated to complete exchange of eight spectrums, counter 14 is reset. When exchange is performed for several frames by the same key, ''1'' is added to contents of counter 13, and they become ''11'', and exchange is performed by the key of decimal indication 3. |
