# US 12,183,356 B2 · Digital encapsulation of audio signals

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- Number: US 12,183,356 B2
- Document ID: US12183356B2
- Status: Granted
- Kind: B2
- Application number: 18/332,148
- Filed: 2023-06-09
- Published: 2024-01-25
- Granted: 2024-12-31
- Earliest claimed: 2018-10-02
- Assignees: Lenbrook Industries Limited
- Applicants: Mqa Limited
- Inventors: Peter Graham Craven; John Robert Stuart
- Web page: https://patentgrep.com/patent/US12183356B2

## CPC

- G10L 19/26: Pre-filtering or post-filtering
- G10L 19/0204: {using subband decomposition}
- 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 21/038: using band spreading techniques
- G10L: SPEECH ANALYSIS TECHNIQUES OR SPEECH SYNTHESIS; SPEECH RECOGNITION; SPEECH OR VOICE PROCESSING TECHNIQUES; SPEECH OR AUDIO CODING OR DECODING

## Abstract

Encoding and decoding systems are described for the provision of high quality digital representations of audio signals with particular attention to the correct perceptual rendering of fast transients at modest sample rates. This is achieved by optimising downsampling and upsampling filters to minimise the length of the impulse response while adequately attenuating alias products that have been found perceptually harmful.

## Claims

### Claim 1

An encoder adapted to furnish a digital audio signal at a transmission sample rate from a signal representing an audio capture, the encoder comprising:
a downsampler that comprises a downsampling filter coupled with a decimator, the downsampling filter having a frequency response having a double zero at each frequency of the digital audio signal that will alias to zero frequency and having a slope at the Nyquist frequency of the transmission sample rate that is more positive than minus thirteen decibels per octave.

### Claim 2 (depends on 1)

An encoder according to claim 1, comprising a flattening filter having a symmetrical frequency response about the Nyquist frequency of the transmission sample rate.

### Claim 3 (depends on 2)

An encoder according to claim 2, wherein the flattening filter has a pole in the z-plane.

### Claim 4 (depends on 2)

An encoder according to claim 2, wherein the transmission sample rate is 44.1 kHz, and a frequency response droop of the encoder does not exceed 1 dB at 20 kHz.

### Claim 5 (depends on 1)

An encoder according to claim 1, wherein the downsampler is configured to downsample an input signal:
from a four times, 4×, sample rate to a two times, 2×, sample rate of the input signal for transmission, or
from a four times, 4×, sample rate to a one time, 1×, sample rate of the input signal for transmission, or
from a two times, 2×, sample rate to a one time, 1×, sample rate of the input signal for transmission.

### Claim 6 (depends on 5)

An encoder according to claim 5, wherein, respectively, the 4× sample rate is 192 KHz or 176.4 kHz, the 2× sample rate is 96 kHz or 88.2 kHz, and the 1× sample rate is 48 kHz or 44.1 kHz.