Methods and apparatus are described for ultrasound transmission. A bit packet is created from received data. A cyclic redundancy check (CRC) is added to the bit packet based on the input data. The bit packet is encoded with forward error correction. The encoded bit packet is block interleaved to create a bit stream. The bit stream is converted into symbols. Each symbol is mapped to a dual tone multi frequency (DTMF). A first audio buffer based upon the DTMF is created. The audio buffer is provided for output.