# US 10,311,882 B2 · Spectral translation/folding in the subband domain

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- Number: US 10,311,882 B2
- Document ID: US10311882B2
- Status: Granted
- Kind: B2
- Application number: 15/988,135
- Filed: 2018-05-24
- Published: 2018-09-27
- Granted: 2019-06-04
- Earliest claimed: 2000-05-23
- Assignees: Dolby International AB
- Applicants: Dolby International AB
- Inventors: Lars G. Liljeryd; Per Ekstrand; Fredrik Henn; Kristofer Kjoerling
- Web page: https://patentgrep.com/patent/US10311882B2

## CPC

- G10L 19/0208: {Subband vocoders}
- G10L 19/0017: {Lossless audio signal coding; Perfect reconstruction of coded audio signal by transmission of coding error (G10L19/24 takes precedence)}
- G10L 19/26: Pre-filtering or post-filtering
- G10L 19/265: {Pre-filtering, e.g. high frequency emphasis prior to encoding}
- G10L 21/038: using band spreading techniques
- G10L 19/0204: {using subband decomposition}
- G10L: SPEECH ANALYSIS TECHNIQUES OR SPEECH SYNTHESIS; SPEECH RECOGNITION; SPEECH OR VOICE PROCESSING TECHNIQUES; SPEECH OR AUDIO CODING OR DECODING

## Abstract

The present invention relates to a new method and apparatus for improvement of High Frequency Reconstruction (HFR) techniques using frequency translation or folding or a combination thereof. The proposed invention is applicable to audio source coding systems, and offers significantly reduced computational complexity. This is accomplished by means of frequency translation or folding in the subband domain, preferably integrated with spectral envelope adjustment in the same domain. The concept of dissonance guard-band filtering is further presented. The proposed invention offers a low-complexity, intermediate quality HFR method useful in speech and natural audio coding applications.

## Claims

### Claim 1

An apparatus for reconstructing a high frequency portion of an audio signal, the apparatus comprising:
a complex exponential modulated analysis filterbank for filtering a low frequency portion of the audio signal to produce a plurality of low frequency complex-valued subband signals, wherein the complex exponential modulated analysis filterbank includes a plurality of decimators;
a high frequency reconstructor that reconstructs the high frequency portion of the audio signal by patching both a real and an imaginary part of a consecutive number of the plurality of low frequency complex-valued subband signals to consecutive subbands of the high frequency portion; and
a complex exponential modulated synthesis filterbank for generating a wideband audio signal by combining the reconstructed high frequency portion of the audio signal with the low frequency portion of the audio signal, wherein the complex exponential modulated synthesis filterbank includes a plurality of interpolators,
wherein the high frequency reconstructor uses a first parameter indicating a quantity of the consecutive number of the plurality of low frequency complex-valued subband signals and a second parameter indicating a reconstruction range start channel.

### Claim 2 (depends on 1)

The apparatus of claim 1 wherein the complex exponential modulated analysis filterbank and the complex exponential modulated synthesis filterbank have L channels.

### Claim 3 (depends on 1)

The apparatus of claim 1 wherein the high frequency reconstructor is configured to reconstruct the high frequency portion of the audio signal with multiple patches.

### Claim 4 (depends on 1)

The apparatus of claim 1 wherein the plurality of decimators each have a decimation factor of M.

### Claim 5 (depends on 1)

The apparatus of claim 1 wherein the plurality of interpolators each have an interpolation factor of M.

### Claim 6 (depends on 2)

The apparatus of claim 2 wherein the plurality of decimators and the plurality of interpolators each have an interpolation factor of M, which is equal to L.

### Claim 7

A method for reconstructing a high frequency portion of an audio signal, the method comprising:
filtering a low frequency portion of the audio signal with a complex exponential modulated analysis filterbank to produce a plurality of low frequency complex-valued subband signals, wherein the filtering includes decimating the plurality of low frequency subband signals;
reconstructing the high frequency portion of the audio signal by patching both a real and an imaginary part of a consecutive number of the plurality of low frequency complex-valued subband signals to consecutive subbands of the high frequency portion; and
generating a wideband audio signal with a complex exponential modulated synthesis filterbank by combining the reconstructed high frequency portion of the audio signal with the low frequency portion of the audio signal, wherein the generating includes interpolating the plurality of low frequency subband signals,
wherein the reconstructing uses a first parameter indicating a quantity of the consecutive number of the plurality of low frequency complex-valued subband signals and a second parameter indicating a reconstruction range start channel.

### Claim 8 (depends on 7)

A non-transitory computer readable medium containing instructions that when executed by a processor perform the method of claim 7.