| 摘要 |
<P>PROBLEM TO BE SOLVED: To reduce delays in limiter operation, with respect to an excessive input signal of precipitous rise, in forming an A/D converter of an output part with a ΣΔ-type analog-digital conversion circuit. <P>SOLUTION: The sound processing apparatus 10 includes a variable gain amplifier (PGA) 1, an A/D converter 2, a limiter detection stage 3 and a gain control part 4. A sound input signal is supplied to the input of the PGA 1, and a sound output signal of the PGA 1 is supplied to the A/D converter 2. The limiter detection stage 3 responds to the sound output signal of the PGA 1 to generate a detection signal. The gain control part 4 responds to the limiter detection signal to control the attenuation of the PGA 1. The A/D converter 2 is formed with a ΣΔ conversion circuit, including a ΣΔ modulator 21 and a decimation filter 22. A high-frequency removal filter 7 extracts a signal generated from intermediate stages of a plurality of delay elements of the decimation filter 22 and supplies it to an input terminal of the limiter detection stage 3. <P>COPYRIGHT: (C)2011,JPO&INPIT |
