Method and device for spectral expansion for an audio signal
A method and device for automatically increasing the spectral bandwidth of an audio signal including generating a “mapping” (or “prediction”) matrix based on the analysis of a reference wideband signal and a reference narrowband signal, the mapping matrix being a transformation matrix to predict high frequency energy from a low frequency energy envelope, generating an energy envelope analysis of an input narrowband audio signal, generating a resynthesized noise signal by processing a random noise signal with the mapping matrix and the envelope analysis, high-pass filtering the resynthesized noise signal, and summing the high-pass filtered resynthesized noise signal with the original an input narrowband audio signal. Other embodiments are disclosed.
1. A device comprising:
a first microphone that measures an ambient sound to generate a first microphone signal;
a second microphone that measures an ear canal region of a user of the device and generates a second microphone signal;
a memory that stores instructions;
a circuit that executes the instructions to perform operations, the operations comprising:
receiving the first microphone signal;
receiving the second microphone signal;
retrieving a mapping matrix, wherein the mapping matrix was formed by doing a least squares fit between a first set of N envelopes and a second set of N envelopes, wherein the first set of N envelopes is formed from a low bandwidth reference signal and the second set of N envelopes is formed from a high bandwidth reference signal, wherein the least squares fit is used to form the mapping matrix;
generating a low frequency energy envelope using the second microphone signal;
generating a sound pressure level from the first microphone signal;
generating a modified microphone signal if the level is greater than a high noise threshold value, wherein the modified microphone signal is generated by applying the mapping matrix to the low frequency energy envelop and combining the result with a modified second microphone signal;
communicating to a remote device; and
sending the modified microphone signal to the remote device.
2. The device according to claim 1 , wherein the first frequency range has a lower value below 5 kHz.
3. The device according to claim 2 , wherein the first microphone is an ear canal microphone.
4. The device according to claim 1 , wherein the second frequency range has a higher frequency value of above 4 kHz.
5. The device according to claim 4 , wherein the second microphone is an ambient sound microphone.
6. The device according to claim 1 , wherein the second microphone signal includes the voice of a user of the device.
7. The device according to claim 1 , further including:
a user interface.
8. The device according to claim 1 , wherein the first microphone is an ear canal microphone,
wherein the second microphone is an ambient sound microphone.
9. The device according to claim 8 , wherein the first frequency range has a lower value of a 5 kHz.
10. The device according to claim 8 , wherein the second frequency range has a higher frequency value of above 4 kHz.
11. The device according to claim 1 , wherein the device is one of a watch, or an eye wear, or a remote control, or a mobile phone, or a hearing aid, or a steering wheel.
12. A method comprising:
receiving a first microphone signal from a first microphone that measures an ambient sound;
receiving a second microphone signal from a second microphone;
generating a first sound pressure level from the first microphone signal;
generating a second sound pressure level from the second microphone signal;
retrieving a mapping matrix, wherein the mapping matrix was formed by doing a least squares fit between a first set of N envelopes and a second set of N envelopes, wherein the first set of N envelopes is formed from a low bandwidth reference signal and the second set of N envelopes is formed from a high bandwidth reference signal, wherein the least squares fit is used to form the mapping matrix;
generating a low frequency energy envelope using the second microphone signal;
generating a sound pressure level from the second microphone signal or from a modified first microphone signal;
generating a first modified microphone signal if the level is greater than a high noise threshold value, wherein the modified microphone signal is generated by applying the mapping matrix to the low frequency energy envelop and combining the result with a modified second microphone signal;
wirelessly connecting to a remote device; and
sending the modified microphone signal to the remote device.
13. The method according to claim 12 , wherein the first frequency range has an upper value and a lower value, wherein the upper value is below 5 KHz.
14. The method according to claim 13 , wherein the lower value is above 100 Hz.
15. The method according to claim 12 , wherein the first microphone is an ear canal microphone that generates the first microphone signal by measuring the acoustic environment in a user's ear canal.
16. The method according to claim 12 , wherein the second microphone is an ambient microphone that generates the second microphone signal by measuring the acoustic environment near user's ear but not in it.