Converting a single-bit audio stream to a stream of symbols with a constant edge rate

Patent metadata

Field	Value
Publication number	US-11107485-B2
Application number	US-201916530798-A
Country	US
Kind code	B2
Filing date	Aug 2, 2019
Priority date	Jan 30, 2017
Publication date	Aug 31, 2021
Grant date	Aug 31, 2021

Abstract

A single-bit audio stream can be converted to a modified single-bit audio stream with a constant edge rate while maintaining a modulation index of the original audio stream using direct mapping. With direct mapping, a pre-filter bank may be combined with a multi-bit symbol mapper to select symbols for the modified audio stream with a constant edge rate per symbol and the same modulation index as the original audio stream. The output of the pre-filter bank may be an audio stream with no consecutive full-scale symbols. Using the output of the pre-filter bank, a multi-bit symbol mapper may use the symbol selector to output a symbol with a constant edge rate per symbol and the same modulation index as the original signal. The symbols may be converted to an analog signal for reproduction of audio content using a transducer.

First claim

What is claimed is:

1. A method, comprising:
filtering an input single-bit audio stream, the single-bit audio stream comprising original audio content formatted as single-bit pulse density modulation (PDM) audio data, the filtering to obtain a symbol selector corresponding to a stream of symbols representing an equivalent audio content as the original audio content of the input single-bit audio stream but with a constant edge rate; and
outputting the stream of symbols to generate a converted single-bit audio stream, the converted single-bit audio stream formatted as single-bit pulse width modulation (PWM) audio data with a constant edge rate, and the converted single-bit audio stream representing the equivalent audio content that is equivalent to the original audio content of the input single-bit audio stream.

2. The method of claim 1 , wherein the step of filtering selects a symbol selector to generate the converted single-bit audio stream without consecutive full-scale symbols.

3. The method of claim 1 , wherein the step of filtering selects the symbol selector to generate equivalent audio content by using multiple representations of a particular quantization symbol.

4. The method of claim 1 , wherein the step of filtering selects the symbol selector to produce the converted single-bit audio stream with a modulation index equivalent to the input single-bit audio stream.

5. The method of claim 1 , wherein the step of filtering modifies a volume of audio content of the input single-bit audio stream.

6. The method of claim 1 , wherein the step of filtering applies magnitude compensation to the input single-bit audio stream.

7. The method of claim 1 , wherein the step of outputting the stream of symbols comprises outputting a plurality of single-bit audio streams based on the symbol selection.

8. The method of claim 1 , wherein the step of filtering comprises noise shaping the symbol selection.

9. The method of claim 1 , wherein the single-bit pulse density modulation (PDM) audio data comprises Direct Stream Digital (DSD) audio data.

Assignees

• Cirrus Logic Int Semiconductor Ltd
• Cirrus Logic Inc

Inventors

• Kamkar Shafagh
• Hester Dylan A
• Duewer Bruce E

Classifications

• H03M5/08 Primary

  Code representation by pulse width · CPC title

• H03M5/14

  Code representation, e.g. transition, for a given bit cell depending on the information in one or more adjacent bit cells, e.g. delay modulation code, double density code · CPC title

• G10L19/00 Primary

  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 title

• H03M5/04

  the pulses having two levels · CPC title

• H03K11/00

  Transforming types of modulations, e.g. position-modulated pulses into duration-modulated pulses · CPC title