Apparatus and method of additive synthesis of digital audio signals using a recursive digital oscillator

• US 7,317,958 B1
• Filed: 03/08/2000
• Issued: 01/08/2008
• Est. Priority Date: 03/08/2000
• Status: Expired due to Fees

• Current Assignee: Regents of the University of California (University of California)
• Original Assignee: Regents of the University of California (University of California)
• Inventors: Hauser, John, Hodes, Todd, Freed, Adrian
• Primary Examiner(s): Tran; Sinh
• Assistant Examiner(s): Flanders; Andrew C
• Application Number:
  US09/521,641
• Time in Patent Office: 2,862 Days
• Field of Search: 381/10, 700/94, 846/22, 846/23, 846/59, 846/61, 708/8, 708/9, 708/251, 708/271
• US Class Current: 700/94
• CPC Class Codes: G10H 1/08 by combining tones G10H1/14, G10H1/16 take precedence; chord G10H1/38
• CPC Class Codes: G10H 2250/635 Waveform resolution or sound quality selection, e.g. selection of high or low sampling rates, lossless, lossy or lossier compression algorithms
• CPC Class Codes: G10H 7/02 in which amplitudes at successive sample points of a tone waveform are stored in one or more memories

Abstract

A method of performing additive synthesis of digital audio signals using a novel recursive digital oscillator includes the step of receiving digital audio signal frames wherein each digital audio signal frame includes a set of frequency, amplitude, and phase components represented as coefficients of variables in a mathematical expression. Each digital audio signal frame thereby includes a frequency coefficient representation. Converted frequency coefficients are formed by linearly re-mapping the bits of the frequency coefficient representation and adding range extension via a shift amount in order to bias audio reproduction accuracy toward low frequency signals. Additive synthesis is then performed with the converted frequency coefficients.

Claims

1. A computer readable medium encoded with computer executable instructions comprising:

a first set of executable instructions to receive digital audio signal frames wherein each digital audio signal frame has a set of specified frequency values expressed as a bit sequence;

a second set of executable instructions to Re-Map said bit sequence to represent lower frequencies with more significant bits and higher frequencies with less significant bits; and

a third set of executable instructions to facilitate additive synthesis of said digital audio signal frames in a reduced-precision recursive digital oscillator

wherein said recursive digital oscillator generates frequency f lying in the range from zero to one-half of a sampling frequency f_s including recursion coefficients xn given by x_n=2x<sub>n−

1</sub>−

ε

x<sub>n−

1</sub>−

x<sub>n−

2</sub>, wherein ε

=2−

2 cos(ω

) and wherein ω

=2π

f/f_s, and

and wherein said Re-Mapping biases the generating frequency of said oscillator, whereby ε

is represented by an unsigned mantissa, m, combined with an unsigned exponent, e, biased so that the actual represented value is ε

=2<sup>2−

e</sup>m.

2. The computer readable medium of claim 1 wherein said first set of executable instructions include instructions to identify a frequency coefficient representation of said specified frequency.

3. The computer readable medium of claim 2 further comprising a fourth set of executable instructions to define said frequency coefficient representation with an exponent characterizing a floating-point range extension.

4. The computer readable medium of claim 3 wherein said fourth set of executable instructions include instructions to specify said exponent to correspond to a right shift amount necessary to correct for precision limitations introduced by a reduced precision processor.