Full-Band Scalable Audio Codec

• US 20120004918A1
• Filed: 07/01/2010
• Published: 01/05/2012
• Est. Priority Date: 07/01/2010
• Status: Active Grant

• Current Assignee: Hewlett-Packard Development Company, L.P. (HP Inc.)
• Original Assignee: Polycom Incorporated (Plantronics, Inc.)
• Inventors: Feng, Jinwei, Chu, Peter
• Granted Patent: US 8,386,266 B2
• Time in Patent Office: Days
• US Class Current: 704/500
• CPC Class Codes: G10L 19/002 Dynamic bit allocation for perceptual audio coders G10L19/032
• CPC Class Codes: G10L 19/0212 using orthogonal transformation
• CPC Class Codes: G10L 19/24 Variable rate codecs, e.g. for generating different qualities using a scalable representation such as hierarchical encoding or layered encoding
• CPC Class Codes: G10L 25/18 the extracted parameters being spectral information of each sub-band

Abstract

A scalable audio codec for a processing device determines first and second bit allocations for each frame of input audio. First bits are allocated for a first frequency band, and second bits are allocated for a second frequency band. The allocations are made on a frame-by-frame basis based on the energy ratio between the two bands. For each frame, the codec transform codes both frequency bands into two sets of transform coefficients, which are then packetized based on the bit allocations. The packets are then transmitted with the processing device. Additionally, the frequency regions of the transform coefficients can be arranged in order of importance determined by power levels and perceptual modeling. Should bit stripping occur, the decoder at a receiving device can produce audio of suitable quality given that bits have been allocated between the bands and the regions of transform coefficients have been ordered by importance.

Claims

1. A scalable audio processing method for a processing device, comprising:

determining first and second bit allocations for a frame of input audio, the first bit allocation allocated for a first frequency band, the second bit allocation allocated for a second frequency band;

transform coding the first frequency band of the frame from a time domain into first transform coefficients in a frequency domain;

transform coding the second frequency band of the frame from the time domain into second transform coefficients in the frequency domain;

packetizing the first and second transform coefficients with the corresponding first and second bit allocations into a packet; and

transmitting the packet with the processing device.

2. The method of claim 1, wherein determining the first and second bit allocations is done frame-by-frame for the input audio.

3. The method of claim 1, wherein determining the first and second bit allocations comprises:

calculating a ratio of energies for the first and second frequency bands of the frame; and

allocating the first and second bit allocations for the frame based on the calculated ratio.

4. The method of claim 1, wherein each of the first and second transform coefficients are arranged in frequency regions, and wherein packetizing each of the first and second transform coefficients comprises:

determining importance of the frequency regions;

ordering the frequency regions based on the determined importance; and

packetizing the frequency regions as ordered.

5. The method of claim 4, wherein determining importance and ordering the frequency regions comprises:

determining a power level for each of the frequency regions; and

ordering the regions from greatest power level to least power level.

6. The method of claim 5, wherein determining the power level further comprises weighting the power levels of the frequency regions using a fixed function based on spectral distances between the frequency regions.

7. The method of claim 1, wherein packetizing comprises packetizing an indication of the first and second bit allocations.

8. The method of claim 1, wherein packetizing comprises packetizing spectrum envelopes for both of the first and second frequency bands.

9. The method of claim 1, wherein packetizing comprises packetizing a lower one of the first and second frequency bands before a higher one for each of the frames.

10. The method of claim 1, wherein transform coding and packetizing comprises:

producing a first version of the frame by transform coding the frame at a first bit rate;

producing a second version of the frame by stripping the first version to a second bit rate lower than the first bit rate; and

packetizing together the first version of the frame along with the second version of a prior frame into the packet.

11. The method of claim 1, wherein the first frequency band is about 0 to about 12 kHz, and wherein the second frequency band is about 12 kHz to about 22 kHz.

12. The method of claim 1, wherein the first frequency band is about 0 to about 12,500 Hz, and wherein the second frequency band is about 13 kHz to about 22 kHz.

13. The method of claim 1, wherein the first and second bit allocations total to available bits of about 64 kbps.

14. The method of claim 1, wherein the transform coefficients comprise coefficients of a Modulated Lapped Transform.

15. A programmable storage device having program instructions stored thereon for causing a programmable control device to perform a scalable audio processing method according to claim 1.

16. A processing device, comprising:

a network interface;

a processor communicatively coupled to the network interface and obtaining input audio, the processor configured to;

determine first and second bit allocations for frames of the input audio, the first bit allocations allocated for a first frequency band, the second bit allocations allocated for a second frequency band;

transform code the first frequency band in a time domain for each of the frames into first transform coefficients in a frequency domain;

transform code the second frequency band in the time domain for each of the frames into second transform coefficients in the frequency domain;

packetize the first transform coefficients for each of the frames with the corresponding one of the first bit allocations into packets;

packetize the second transform coefficients for each of the frames with the corresponding one of the second bit allocations into the packets; and

transmit the packets with the network interface.

17. The device of claim 16, wherein the processing device is selected from the group consisting of an audio conferencing endpoint, a videoconferencing endpoint, an audio playback device, a personal music player, a computer, a server, a telecommunications device, a cellular telephone, and a personal digital assistant.

18. An audio processing method for a processing device, comprising:

receiving packets for frames of input audio, each of the packets having first transform coefficients in a frequency domain for a first frequency band of one of the frames and having second transform coefficients in the frequency domain for a second frequency band of the frame;

determining first and second bit allocations for the frames in each of the packets, each of the first bit allocations allocated for the first frequency band of the frame in the packet, each of the second bit allocations allocated for the second frequency band of the frame in the packet;

inverse transform coding the first and second transform coefficients for each of the frames in the packets into output audio;

determining whether bits are missing from the first and second bit allocations for each of the frames in the packets; and

filling in audio into any of the bits determined missing.

19. The method of claim 18, wherein receiving the packets comprises receiving a spectrum envelope for each of the first and second frequency bands of the frames, and wherein filling in audio comprises scaling an audio signal with the spectrum envelope.

20. An audio processing method for a processing device, comprising:

producing first versions of consecutive frames of input audio by transform coding each of the consecutive frames at a first bit rate;

producing second versions of each of the consecutive frames by stripping each of the first versions to a second bit rate lower than the first bit rate;

packetizing each of the first versions of the consecutive frames along with the second version of a prior one of the consecutive frames into packets.

transmitting the packets with the processing device.

21. An audio processing method for a processing device, comprising:

receiving packets for consecutive frames of input audio, each of the packets having a first version of one of the consecutive frames and having a second version of a prior one of the consecutive frames, each of the first versions including the one frame transform coded at a first bit rate, each of the second versions including the first version of the prior frame stripped to a second bit rate lower than the first bit rate;

decoding each of the packets;

detecting a packet error for one of the packets received;

reproducing a missing frame for the one packet by using the second version of the missing frame for the one packet from a prior one of the packets received; and

producing output audio with the first version of the frames and the reproduced missing frame.