Real-Time Audio Buffering for Telephone Applications
On ordinary phones, if you miss something, it is gone forever. With real-time audio buffering, you can hear what you have been missing. Best of all, the operation is intuitive, requiring little or no action on the user's part.
Background & Objective: The cell phone market is extremely competitive. Many phones have similar capabilities and prices. To stand out in the crowd, unique features are needed. We propose real-time audio buffering as an inexpensive feature users will appreciate.
Real-time audio buffering senses when the phone is removed from the ear. When the phone is returned, the missed incoming audio is played back, but at a rate faster than real-time. Very quickly, the phone catches back up to real-time, and the user misses nothing, despite the distraction. The ear sensor also allows us to create an elegant "instant-replay" function. Briefly move the phone away from the ear, and it automatically replays the last few seconds. Repeating this gesture skips successively further back in time.
Technical Discussion: Real-time audio buffering uses a capacitive proximity sensor to determine when the phone is near the ear. The sense electrode is created by coating the inside of the ear piece with a conductive coating as might normally be applied for shielding purposes. In addition, the remainder of the case interior is similarly coated and connected to the phone's internal ground. Holding the phone up to an ear capacitively couples the ear sense electrode to the phone's ground through the user (via ear and hand). By measuring the change in capacitance, we can easily detect the phone proximity to the ear.
The audio section constantly stores incoming audio in a circular buffer. Normally, the "play pointer" immediately tracks the "record pointer". When the phone is removed from the ear, the record pointer continues adding incoming audio, but the play pointer is halted until the phone is returned to the ear. To help give the user the context of the conversation, it helps to move the play pointer a little further back in time each time the phone is removed from the ear. This implements the instant-replay function as a side benefit. When the play pointer is behind the record pointer, we speed up play back via a pitch-preserving technique and skip silent intervals.
Recently, we have noted other uses for the ear sensor, in addition to the buffering function. Intelligent display control improves both power consumption and functionality by automatically turning off the display when the phone is pressed against the ear, and turning it on when removed.
Technology Areas:
Sensor and Data Systems
Audio Video Processing
Off the Desktop Interaction and Display
Modification Date: June 13, 2008