# US 12,014,746 B2 · Method and apparatus for processing an audio signal, audio decoder, and audio encoder to filter a discontinuity by a filter which depends on two fir filters and pitch lag

> Agents: this data is available as JSON from the patentgrep API and MCP server — see https://patentgrep.com/llms.txt

- Number: US 12,014,746 B2
- Document ID: US12014746B2
- Status: Granted
- Kind: B2
- Application number: 17/580,578
- Filed: 2022-01-20
- Published: 2022-05-12
- Granted: 2024-06-18
- Earliest claimed: 2014-07-28
- Assignees: Fraunhofer-Gesellschaft zur Foerderung der angewandten Forschung e. V.
- Applicants: Fraunhofer-Gesellschaft zur Foerderung der angewandten Forschung e.V.
- Inventors: Emmanuel Ravelli; Manuel Jander; Grzegorz Pietrzyk; Martin Dietz; Marc Gayer
- Web page: https://patentgrep.com/patent/US12014746B2

## CPC

- G10L 19/06: Determination or coding of the spectral characteristics, e.g. of the short-term prediction coefficients
- G10L 19/26: Pre-filtering or post-filtering
- G10L 19/005: Correction of errors induced by the transmission channel, if related to the coding algorithm
- G10L 19/022: Blocking, i.e. grouping of samples in time; Choice of analysis windows; Overlap factoring
- G10L 19/03: Spectral prediction for preventing pre-echo; Temporary noise shaping [TNS], e.g. in MPEG2 or MPEG4
- G10L 19/12: the excitation function being a code excitation, e.g. in code excited linear prediction [CELP] vocoders
- G10L 19/20: using sound class specific coding, hybrid encoders or object based coding
- G10L 21/0364: for improving intelligibility
- G11B 27/038: Cross-faders therefor
- H04B 1/1027: {assessing signal quality or detecting noise/interference for the received signal}
- G10L: SPEECH ANALYSIS TECHNIQUES OR SPEECH SYNTHESIS; SPEECH RECOGNITION; SPEECH OR VOICE PROCESSING TECHNIQUES; SPEECH OR AUDIO CODING OR DECODING
- G11B: INFORMATION STORAGE BASED ON RELATIVE MOVEMENT BETWEEN RECORD CARRIER AND TRANSDUCER (recording measured values in a way that does not require playback through a transducer G01D9/00; recording or playback apparatus using mechanically marked tape, e.g. punched paper tape, or using unit records, e.g. punched or magnetically marked cards G06K; transferring data from one type of record carrier to another G06K1/18; circuits for coupling output of reproducer to radio receiver H04B1/20; gramophone pick-ups or like acoustic electromechanical transducers or circuits therefor H04R)
- H04B: TRANSMISSION

## Abstract

A method is described that processes an audio signal. A discontinuity between a filtered past frame and a filtered current frame of the audio signal is removed using linear predictive filtering.

## Claims

### Claim 1

A method for processing an audio signal, the method comprising:
filtering audio frames of the audio signal using the following filter:
H(z)=(1−B(z))/(1−C(z)·z−T)
where B(z) and C(z) are two FIR filters and the H(z) filter parameters are the coefficients of the FIR filters B(z) and C(z), and T indicates the pitch lag, wherein filtering the audio frames of the audio signal comprises filtering a past frame of the audio signal using a set of first filter parameters for obtaining a filtered past frame, and filtering a current frame of the audio signal using a set of second filter parameters for obtaining a filtered current frame, and
removing a discontinuity between the filtered past frame and the filtered current frame of the audio signal using a linear predictive filter,
wherein initial states of the linear predictive filter are obtained by filtering a last part of the past frame using the set of second filter parameters.

### Claim 2 (depends on 1)

The method of claim 1, further comprising estimating the linear predictive filter using the audio signal.

### Claim 3 (depends on 2)

The method of claim 2, wherein estimating the linear predictive filter comprises estimating the linear predictive filter based on the past and/or current frame of the audio signal or based on the filtered past frame of the audio signal using the Levinson-Durbin algorithm.

### Claim 4 (depends on 1)

The method of claim 1, wherein the linear predictive filter comprises a linear predictive filter of an audio codec.

### Claim 5

A non-transitory digital storage medium having stored thereon a computer program product for performing, when run on a computer, a method for processing an audio signal, the method comprising:
filtering audio frames of the audio signal using the following filter:
H(z)=(1−B(z))/(1−C(z)·z−T)
where B(z) and C(z) are two FIR filters and the H(z) filter parameters are the coefficients of the FIR filters B(z) and C(z), and T indicates the pitch lag, wherein filtering the audio frames of the audio signal comprises filtering a past frame of the audio signal using a set of first filter parameters for obtaining a filtered past frame, and filtering a current frame of the audio signal using a set of second filter parameters for obtaining a filtered current frame, and
removing a discontinuity between the filtered past frame and the filtered current frame of the audio signal using a linear predictive filter,
wherein initial states of the linear predictive filter are obtained by filtering a last part of the past frame using the set of second filter parameters.

### Claim 6

An apparatus for processing an audio signal,
wherein the apparatus comprises a processor configured to:
filter audio frames of the audio signal using the following filter:
H(z)=(1−B(z))/(1−C(z)·z−T)
where B(z) and C(z) are two FIR filters and the H(z) filter parameters are the coefficients of the FIR filters B(z) and C(z), and T indicates the pitch lag, wherein filtering the audio frames of the audio signal comprises
filtering a past frame of the audio signal using a set of first filter parameters for obtaining a filtered past frame, and
filtering a current frame of the audio signal using a set of second filter parameters for obtaining a filtered current frame, and
remove a discontinuity between the filtered past frame and the filtered current frame of the audio signal using a linear predictive filter,
wherein initial states of the linear predictive filter are obtained by filtering a last part of the past frame using the set of second filter parameters.

### Claim 7 (depends on 6)

An audio decoder, comprising an apparatus of claim 6.

### Claim 8 (depends on 6)

An audio encoder, comprising an apparatus of claim 6.