Distributed audio coding for wireless hearing aids

• US 20080306745A1
• Filed: 05/30/2008
• Published: 12/11/2008
• Est. Priority Date: 05/31/2007
• Status: Active Grant

• Current Assignee: Ecole polytechnique fãdãrale de lausanne epfl (Schweizerische Eidgenossenschaft)
• Original Assignee: Ecole polytechnique fãdãrale de lausanne epfl (Schweizerische Eidgenossenschaft)
• Inventors: VETTERLI, Martin, ROY, Olivier
• Granted Patent: US 8,077,893 B2
• Time in Patent Office: Days
• US Class Current: 704/500
• CPC Class Codes: G10L 19/008 Multichannel audio signal coding or decoding using interchannel correlation to reduce redundancy, e.g. joint-stereo, intensity-coding or matrixing
• CPC Class Codes: G10L 19/0204 using subband decomposition
• CPC Class Codes: H04R 25/552 Binaural

Abstract

The aim of the invention is to provide inter-channel level differences ICLD related to audio signals for hearing aids. This aim is achieved by a method for computing ICLD from a first and second audio source signals, the first source signal being wired with a first processing module and the second source signal being wired with a second processing module, the second processing module receiving wirelessly information from the first processing module, this method comprising the steps of: acquiring first samples of the first sound signal by the first processing module, defining a first time frame, converting the first time frame into first frequency bands and grouping them into two first frequency sub-bands, calculating a first power estimate of each first frequency sub-bands, encoding and transmitting same to the second processing module, acquiring second samples of the second sound signal by the second processing module,

• defining a second time frame comprising acquired samples, converting same into second frequency bands, grouping them into two second frequency sub-bands,
• calculating a second power estimate of each second frequency sub-bands, receiving and decoding the encoded first power estimates, computing for each frequency sub-band, an ICLD by subtracting the first decoded power estimates and the second power estimates.

Claims

1. Method for computing inter-channel level differences from a first audio source signal x₁ and a second source signal x₂, the first source signal x₁ being wired with a first processing module PM1 and the second source signal x₂ being wired with a second processing module PM2, the second processing module PM2 receiving wirelessly information from the first processing module PM1, this method comprising the steps of:

(a) acquiring first samples of the first sound signal x₁ by the first processing module PM1,

(b) defining a first time frame comprising several acquired samples of the first source signal,

(c) converting the first time frame into first frequency bands,

(d) grouping the first frequency bands into at least two first frequency sub-bands,

(e) calculating a first power estimate of each first frequency sub-bands,

(f) encoding the first power estimates and transmitting the encoded first power estimates to the second processing module PM2,

(g) acquiring second samples of the second sound signal x₂ by the second processing module PM2,

(h) defining a second time frame comprising several acquired samples of the second source signal,

(i) converting the second time frame into second frequency bands,

(j) grouping the second frequency bands into at least two second frequency sub-bands,

(k) calculating a second power estimate of each second frequency sub-bands,

(l) receiving and decoding the encoded first power estimates,

(m) computing for each frequency sub-band, an inter-channel level difference by subtracting the first decoded power estimates and the second power estimates.

2. Method of claim 1, further comprising the steps of:

(a) encoding the second power estimates and transmitting the encoded second power estimates to the first processing module PM1,

(b) receiving and decoding the encoded second power estimates by the first processing module PM1,

(c) calculating for each frequency sub-band, an inter-channel level difference by subtracting the first power estimates and the second decoded power estimates.

3. Method of claim 1, in which the step of encoding comprises the following steps, for each power estimate:

(a) quantizing the power estimate within a predefined range,

(b) applying a modulo function on the quantized power estimate, the modulo value being specific for each frequency sub-band to produce an index, the range of said index being lower than the range of the quantized power estimate,

(c) the index forming the encoded power estimate.

4. Method of claim 3, in which the step of decoding comprises the following steps, for each encoded first power estimate:

(a) quantizing the second power estimate within the predefined range,

(b) defining a sub-range of modulo in which the quantized second power estimate is located within the predefined range,

(c) using the defined sub-range and the encoded first power estimate to calculate the decoded first power estimate.

5. Method to produce a rebuild first input signal using inter-channel level differences as computed in claim 1, further comprising the steps of:

(a) producing output sound sub-bands based on the inter-channel level differences and the second frequency sub-bands

(b) converting the output sound sub-bands into time domain to produce the rebuild first input signal output sound signal {circumflex over (x)}₁.