Method and system for recognizing speech commands using background and foreground acoustic models

An electronic device, comprising:

• one or more processors;
• memory;
• and
• one or more programs, wherein the one or more programs are stored in the memory and configured to be executed by the one or more processors, the one or more programs including an operating system and instructions that when executed by the one or more processors cause the electronic device to:
• generate a background acoustic model for a sound using a first sound sample, wherein the sound in the background acoustic model is represented as monophones and the background acoustic model is characterized by a first precision metric that is less than a first predefined inverse variance value, and wherein the first precision metric corresponds to an inverse of a variance of the background acoustic model;
• generate a foreground acoustic model for the sound using a second sound sample, wherein the sound in the foreground acoustic model is represented as triphones and the second sound sample characterized by higher precision phonemes than the first sound sample, resulting in the foreground acoustic model being characterized by a second precision metric that is greater than a second predefined inverse variance value, and wherein the second precision metric corresponds to an inverse of a variance of the foreground acoustic model;
• receive a third sound sample corresponding to the sound;
• decode the third sound sample by:
• using the foreground acoustic model and the background acoustic model, assigning a first weight to the third sound sample corresponding to a probability that the sound sample originated in a foreground;
• determining if the first weight meets predefined criteria for assigning the third sound sample to the foreground;
• in accordance with a determination that the first weight meets the predefined criteria, interpreting the third sound sample as a portion of a speech command originating from a user of the electronic device;
• and
• in accordance with a determination that the first weight does not meet the predefined criteria, rejecting the third sound sample as having originated in the background rather than having originated from the user.

A non-transitory computer readable storage medium storing one or more programs, the one or more programs comprising instructions, which when executed by an electronic device with one or more processors and memory, cause the electronic device to:

• generate a background acoustic model for a sound using a first sound sample, wherein the sound in the background acoustic model is represented as monophones and the background acoustic model is characterized by a first precision metric that is less than a first predefined inverse variance value, and wherein the first precision metric corresponds to an inverse of a variance of the background acoustic model;
• generate a foreground acoustic model for the sound using a second sound sample, wherein the sound in the foreground acoustic model is represented as triphones and the second sound sample characterized by higher precision phonemes than the first sound sample, resulting in the foreground acoustic model being characterized by a second precision metric that is greater than a second predefined inverse variance value, and wherein the second precision metric corresponds to an inverse of a variance of the foreground acoustic model;
• receive a third sound sample corresponding to the sound;
• decode the third sound sample by:
• using the foreground acoustic model and the background acoustic model, assigning a first weight to the third sound sample corresponding to a probability that the sound sample originated in a foreground;
• determining if the first weight meets predefined criteria for assigning the third sound sample to the foreground;
• in accordance with a determination that the first weight meets the predefined criteria, interpreting the third sound sample as a portion of a speech command originating from a user of the electronic device;
• and
• in accordance with a determination that the first weight does not meet the predefined criteria, rejecting the third sound sample as having originated in the background rather than having originated from the user.