29. 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.
29. 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. 35. The method of claim 29 , further comprising filtering the first signal to generate an input signal substantially within a fourth range of frequencies.