Method and apparatus for adding audible noise with time varying volume to audio devices

A method for adding a noise signal to an audio signal, comprising:

• receiving a first signal;
• selecting from the first signal, a volume envelope corresponding to sound intensities of a first range of frequencies;
• generating a noise signal, wherein the noise signal corresponds to noise substantially within a second range of frequencies;
• generating a modulated noise signal, wherein the modulated noise signal is substantially proportional to the product of the noise signal multiplied by the volume envelope;
• generating a summation signal, wherein the summation signal is substantially proportional to the sum of a weighted modulated noise signal and a weighted first signal;
• and
• filtering the summation signal to generate an output signal comprised of a third range of frequencies.

An audio system, comprising:

• a filtered volume determiner configured to receive a first signal, wherein the filtered volume determiner is configured to generate a second signal corresponding to a volume envelope for a first range of selected frequencies of the first signal;
• a filtered noise generator configured to generate a third signal corresponding to noise substantially within a second range of selected frequencies;
• a signal modulator, coupled to the filtered volume determiner and to the filtered noise generator, wherein the signal modulator is configured to receive from the filtered volume determiner the second signal, and wherein the signal modulator is configured to receive from the filtered noise generator the third signal, and wherein the signal modulator is configured to generate a fourth signal substantially similar to a product of a weighted second signal and a weighted third signal;
• a mixer, coupled to the signal modulator, wherein the mixer is configured to receive from the signal modulator the fourth signal, and wherein the mixer is configured to receive a fifth signal substantially similar to the first signal, and wherein the mixer is configured to generate a sixth signal substantially similar to a sum of a weighted fourth signal and a weighted fifth signal;
• an input filter coupled to receive an audio signal and generate a filtered input signal substantially within a fourth range of selected frequencies;
• and
• a splitter configured to receive the filtered input signal, wherein the splitter generates the first signal and the fifth signal, and wherein the first signal, the fifth signal and the filtered input signal are all substantially similar.