Tone signal processing apparatus for PCM waveform interpolation and filtering

• US 5,218,155 A
• Filed: 03/29/1990
• Issued: 06/08/1993
• Est. Priority Date: 03/30/1990
• Status: Expired due to Fees

• Current Assignee: Kabushiki Kaisha Kawai Gakki Seisakusho
• Original Assignee: Kabushiki Kaisha Kawai Gakki Seisakusho
• Inventors: Saito, Tsutomu
• Primary Examiner(s): Shoop, Jr., William M.
• Assistant Examiner(s): DONELS, JEFFREY
• Application Number:
  US07/677,249
• Time in Patent Office: 1,167 Days
• Field of Search: 84/603, 84/607, 84/608, 84/622, 84/623, 84/647, 84/659, 84/661, 84/DIG. 9
• US Class Current: 84/623
• CPC Class Codes: G10H 1/08 by combining tones G10H1/14, G10H1/16 take precedence; chord G10H1/38
• CPC Class Codes: G10H 2250/631 Waveform resampling, i.e. sample rate conversion or sample depth conversion waveform decimation G10H2250/611
• CPC Class Codes: G10H 7/02 in which amplitudes at successive sample points of a tone waveform are stored in one or more memories
• CPC Class Codes: Y10S 84/09 Filtering

Abstract

A tone signal processing apparatus for time-divisionally reading out tone signal waveforms in units of different channels from a waveform memory for storing a plurality of kinds of tone signal waveforms each consisting of tone data at a plurality of sampling points. An arithmetic circuit for multiplying each of two input data with a predetermined coefficient, and adding the products, and a memory circuit for storing an output from the arithmetic circuit are arranged. The arithmetic circuit is alternately operated in two arithmetic modes, i.e., an interpolation arithmetic mode for multiplying each of two tone data at adjacent sampling points read out from the waveform memory with an interpolation coefficient, and adding the products to obtain an interpolated value obtained by interpolating between the adjacent sampling points, and a filter arithmetic mode for multiplying each of the interpolated value and a previous filter output obtained from the filter circuit with a filter coefficient to obtain a filter output. The filter coefficient is changed in units of channels to provide different filter characteristics in units of channels.

Claims

1. A tone processing circuit comprising:

a waveform memory for storing a tone signal waveform including tone data at a plurality of sampling points;

an arithmetic circuit for multiplying each of two adjacent sampling points with a predetermined coefficient, and adding the products to produce an output; and

a memory circuit for storing the output from said arithmetic circuit,

wherein said arithmethic circuit is alternately operated in two arithmetic modes including,

an interpolation arithmetic mode for multiplying each of the two adjacent sampling points read out from said waveform memory with an interpolation coefficient, and adding the products to obtain an interpolated value obtained by interpolating between the two adjacent sampling points, and

a filter arithmetic mode for multiplying the interpolated value and a previous filter output obtained from said memory circuit with a filter coefficient, and adding the products to obtain a filter output;

said waveform memory having memory areas for a plurality of channels which respectively store a plurality of different tone signal waveforms, wherein the plurality of different tone signal waveforms of the plurality of channels are time-divisionally read out, the filter coefficient varying for each of the plurality of channels.

2. The circuit according to claim 1, wherein the interpolated value is calculated by

3. The circuit according to claim 1, further comprising:

a selection circuit for selecting, in the interpolation arithmetic mode, the two adjacent sampling points read out from said waveform memory, and the interpolation coefficient, and in the filter arithmetic mode, the interpolated value, the previous filter output obtained from said memory circuit, and the filter coefficient.

4. The circuit according to claim 1, said arithmetic circuit including:

first and second multipliers, and

an adder for adding outputs from said multipliers, such that in the interpolation arithmetic mode, said first multiplier multiples one of the two adjacent sampling points read out from said waveform memory with the interpolation coefficient, and said second multiplier multiples the other one of the two adjacent sampling points read out from said waveform memory with an inverse of the interpolation coefficient; and

in the filter arithmetic mode, said first multiplier multiplies the interpolated value with the filter coefficient, and said second multiplier multiplies the previous filter output obtained from said memory circuit with an inverse of the filter coefficient.

5. The circuit according to claim 4, further comprising an inverter for outputting the inverse of the interpolation and the filter coefficients on the basis of the interpolation coefficient and the filter coefficient.

6. A tone signal processing apparatus comprising:

an arithmetic circuit including, sampling point interpolation means for performing a sampling point interpolation arithmetic operation utilizing a predetermined equation for tone data read out from a waveform memory and for storing a tone signal waveform consisting of tone data at a plurality of sampling points, and

filter means for performing a filter arithmetic operation utilizing an equation for adding, to a previous filter output value, a value obtained by multiplying a difference between a sampling point interpolated value obtained from said sampling point interpolation means and a previous filter output value with a predetermined filter coefficient,

wherein said arithmetic circuit time-divisionally performs the sampling point interpolation arithmetic operation and the filter arithmetic operation,

said waveform memory having memory areas for a plurality of channels, which respectively store a plurality of different tone signal waveforms, wherein the plurality of different tone signal waveforms of the plurality of channels are time-divisionally read out, the filter coefficient varying for each of the plurality of channels.

7. The circuit according to claim 6, wherein the sampling point interpolation arithmetic operation is calculated by

8. A tone processing circuit comprising:

waveform memory means for storing a plurality of waveforms, each waveform including a plurality of sampling points;

addressing means, responsive to key information for generating successive addresses, including an integral address part and a decimal address part, wherein the integral address part is used to read tone data representative of the plurality of stored waveforms of said waveform memory means;

arithmetic means for performing sampling point interpolation on the plurality of stored waveforms using the decimal address part as a first coefficient for the tone data read from said waveform memory means to generate interpolated tone data;

time-divisional means for operating said arithmetic means as a tone filter for performing a filter arithmetic operation on the plurality of stored waveforms using a second coefficient in place of said first coefficient;

channel means, including a plurality of channels for outputting the plurality of interpolated and filtered waveforms through said arithmetic means, wherein said plurality of interpolated and filtered waveforms are time-divisionally output and said second coefficient varies for each of the plurality of channels;

accumulation means for accumulating said plurality of interpolated and filtered waveforms in said plurality of channels to generate accumulated waveform data; and

conversion means for converting said plurality of accumulated waveform data into an analog tone signal.

9. The tone processing circuit of claim 8, wherein said second coefficient is responsive to key scale data generated by a keyboard operation.

10. The tone processing circuit of claim 8, wherein said second coefficient is responsive to key touch data generated by a keyboard operation.