Adaptive forward error correction redundant payload generation

A fault tolerant audio encoder for encoding an audio signal into a fault tolerant version of the audio signal, the encoder including a processor with instructions embodied therein to be executed by the processor, the instructions providing:

• a primary encoder for encoding the audio signal in a first encoding format, comprising a first series of audio frames, with each audio frame including encoded information for a series of frequency bands, the encoding including determining a series of power envelopes, allocation data, and spectrum data for the frequency bands;
• an intelligent detector for selecting a subset of the frequency bands for each of the audio frames by determining content type of each audio frame, the content type being one of a vowel type and a fricative type, and selecting the subsets for each audio frame based on the determined content types;
• a redundant encoder for encoding the audio signal in a redundant encoding format comprising a second series of audio frames, with each audio frame including only encoded information of the power envelopes for the selected subset of frequency bands of the audio frame;
• and
• a forward error correction encoder for combining the first encoding format and the redundant encoding format, the forward error correction encoder also transmitting frames of the forward error encoded audio stream over the lossy packet switched network.

A method of decoding a received fault tolerant audio signal, received as packets in a lossy packet switching network environment, the fault tolerant audio signal including:

• a first series of audio frames, with each audio frame including spectral encoded information for a series of frequency bands;
• a second series of audio frames, with each audio frame including only selected subsets of power envelopes for frequency bands of the audio frame, the fault tolerant audio signal comprising a combination of the first series of audio frames and the second series of audio frames encoded using forward error encoding, the subsets being selected based on determined content type of each audio frame, the content type being one of a vowel type and a fricative type,
• the method including the steps of:
• detecting a lost packet;
• replicating the spectral data from a previous frame;
• modulating the replicated spectral data by the power envelope information for a current frame to generate a lost frame of the received audio signal to replace the lost packet;
• and
• inserting the generated lost frame into the received audio signal for subsequent playback.

A method of decoding a received fault tolerant audio signal, received as packets in a lossy packet switching network environment, the fault tolerant audio signal including:

• a first series of audio frames, with each audio frame including spectral encoded information for a series of frequency bands;
• a second series of audio frames, with each audio frame including only selected subsets of power envelopes for frequency bands of the audio frame, the fault tolerant audio signal comprising a combination of the first series of audio frames and the second series of audio frames encoded using forward error encoding, the subsets being selected based on determined content type of each audio frame, the content type being one of a vowel type and a fricative type,
• the method including the steps of:
• detecting a lost packet;
• generating a current frame from the power envelope information for a current frame and a spectral noise generator;
• and
• inserting the generated lost frame into the received audio signal for subsequent playback.

A method of encoding audio information for forward error correction reconstruction of a transmitted audio stream over a lossy packet switched network, the method including the steps of:

• dividing the audio stream into audio frames;
• determining a series of corresponding audio frequency bands for said audio frames;
• determining a series of power envelopes for the frequency bands as part of encoding the audio frames, the encoding also including determining allocation data and spectrum data for the frequency bands;
• determining phase data and magnitude data from the audio frequency bands for the audio frames;
• determining content type of each audio frame, the content type being one of a vowel type and a fricative type;
• encoding a selected subset of the power envelopes as low bit rate versions of the audio frames in redundant transmission frames, the subset of the power envelopes for each of the audio frames being selected based on the content type of the audio frames;
• encoding the phase and magnitude data as part of the redundant transmission frame;
• performing forward error correction encoding for the audio stream by combining encoded audio frames with the encoded redundant transmission frames;
• and
• transmitting frames of the forward error encoded audio stream over the lossy packet switched network.