Digital Audio Synthesizer

• US 20130103173A1
• Filed: 06/21/2011
• Published: 04/25/2013
• Est. Priority Date: 06/25/2010
• Status: Active Grant

• Current Assignee: Universite De Lorraine (Government of France), Inria Institut National de Recherche EN Informatique et EN Automatique
• Original Assignee: Universite De Lorraine (Government of France), Inria Institut National de Recherche EN Informatique et EN Automatique
• Inventors: Pierron, Laurent, Di Martino, Joseph
• Granted Patent: US 9,170,983 B2
• Time in Patent Office: Days
• US Class Current: 700/94
• CPC Class Codes: G06F 17/00 Digital computing or data processing equipment or methods, specially adapted for specific functions information retrieval, database structures or file system structures therefor G06F16/00
• CPC Class Codes: G10H 2210/155 Musical effects
• CPC Class Codes: G10H 2210/285 Electromechanical effectors therefor, i.e. using springs or similar electromechanical audio delay units
• CPC Class Codes: G10H 2250/005 Algorithms for electrophonic musical instruments or musical processing, e.g. for automatic composition or resource allocation
• CPC Class Codes: G10H 2250/031 Spectrum envelope processing
• CPC Class Codes: G10H 2250/235 Fourier transform; Discrete Fourier Transform [DFT]; Fast Fourier Transform [FFT]
• CPC Class Codes: G10H 2250/281 Hamming window
• CPC Class Codes: G10H 2250/471 General musical sound synthesis principles, i.e. sound category-independent synthesis methods
• CPC Class Codes: G10L 13/02 Methods for producing synthetic speech; Speech synthesisers
• CPC Class Codes: G10L 13/04 Details of speech synthesis systems, e.g. synthesiser structure or memory management
• CPC Class Codes: G10L 19/00 Speech or audio signals analysis-synthesis techniques for redundancy reduction, e.g. in vocoders; Coding or decoding of speech or audio signals, using source filter models or psychoacoustic analysis in musical instruments G10H
• CPC Class Codes: G10L 19/022 Blocking, i.e. grouping of samples in time; Choice of analysis windows; Overlap factoring
• CPC Class Codes: G10L 2021/0135 Voice conversion or morphing
• CPC Class Codes: G10L 25/18 the extracted parameters being spectral information of each sub-band

Abstract

The invention relates to a digital audio synthesizer that includes: an input memory for receiving a sequence of digital data representing the amplitude spectrum of an audio signal over consecutive and overlapping time windows; a computer (120) that is set up to receive, as an input, a draft digital data set for a active window including amplitude-extrapolated data at the start of a window and zero values for the rest of the window, and to establish, as a response, a digital representation of the discrete complex Fourier transform for said set; a dialer (130) that is set up to combine the amplitude spectrum input, corresponding to the active window in question, with the digital representation predetermined by the computer, and to call the computer (120) with the resulting data in order to establish a digital representation of the corresponding complex inverse discrete Fourier transform that provides a set of estimated digital data related to the active window in question; and an adder (140) for selectively accumulating the estimated digital data that corresponds to a single period of time. The dialer (130) is set up to calculate an auxiliary digital data set (Xi(n)) by taking the active set (z(n)) of estimated digital data divided by a window function on each time window. The adder (140) is set up to add the active set of estimated digital data multiplied by the window function (H) having the preceding value from the accumulated total. Said digital audio synthesizer also includes an extrapolator (110) that is set up to calculate the draft digital data set for an active window from the auxiliary digital data set for the preceding window, said auxiliary digital data set being selectively multiplied by the square of the window function.

Claims

1. An audio digital synthesizer, comprising:

an input memory for receiving a series of digital data representing the amplitude spectrum of an audio signal, over consecutive and overlapping time windows,

a computer that is set up to receive, as an input, a draft digital data set for an active window comprising amplitude-extrapolated data at the start of the window and zero values for the rest of the window, and to establish, as a response, a digital representation of the complex discrete Fourier transform for said set,

a dialer that is set up to combine the amplitude spectrum input, corresponding to the active window in question, with the digital representation predetermined by the computer, and to call the computer with the resulting data in order to establish a digital representation of the corresponding complex inverse discrete Fourier transform that provides a set of estimated digital data relative to the active window in question; and

an adder for selectively accumulating the estimated digital data that corresponds to a single period of time,

characterized in that;

the dialer is set up to calculate an auxiliary digital data set by taking the active set of estimated digital data divided by a window function on each time window;

the adder is set up to add the active set of estimated digital data multiplied by the window function having the preceding value from the accumulated total; and

in that it comprises an extrapolator that is set up to calculate the draft digital data set for an active window from the auxiliary digital data set for the preceding window, said auxiliary digital data set being selectively multiplied by the square of the window function.

2. The synthesizer according to claim 1, wherein the extrapolator calculates the draft digital data set for an active window by shifting the auxiliary digital data set from the previous window to the left by L indices, setting the last L samples of the shifted set to zero, then multiplying term to term by the square of the window function.

3. The synthesizer according to claim 1, wherein the window function comprises a normalized Hamming window function.

4. The synthesizer according to claim 1, also comprising a spectrometer arranged to calculate a digital data series that represents the amplitude spectrum of an audio signal as an input, and to transmit that data to the input memory.

5. The synthesizer according to claim 4, comprising a component placed between the spectrometer and the input memory capable of modifying the digital data that represents the amplitude spectrum as an input, and to transmit the modified amplitude spectrum data to the input memory.