Systems and methods for simulation of mixing in air of recorded sounds
A mixing signal processing technique modifies digital audio recordings to simulate the linear and nonlinear effects of propagation and mixing of sounds in air. When multiple sounds or complex sounds comprised of multiple frequencies in the audible spectrum propagate in such a nonlinear medium, they transfer energy into sound at new frequencies given by the sums and differences of the original signal frequencies. The mixing signal processing technique may improve the ability of a system to reproduce the effects of a live performance using a digital audio recording.
1. A method for simulating propagation and mixing of sounds in air, the method comprising:
selecting a relationship between a virtual audio listener location and a virtual source location within an audio interaction volume, the audio interaction volume associated with a first audio waveform, the first audio waveform including audio generated using a first audio isotropic source; and
generating a second audio waveform using the first audio waveform, the second audio waveform including a plurality of simulated intermodulation products corresponding to the relationship between the virtual audio listener location and the virtual source location.
2. The method of claim 1 , the first audio waveform further including audio generated using a second isotropic audio source.
3. The method of claim 1 , further including generating a simulated mixed output waveform, the generating including:
applying a first gain to the first audio waveform to generate a first amplified waveform;
applying a second gain to the second audio waveform to generate a second amplified waveform; and
summing the first amplified waveform and the second amplified waveform to generate the simulated mixed output waveform.
4. The method of claim 3 , further including transducing the simulated mixed output waveform into audible sounds.
5. The method of claim 1 , further including:
identifying an audio sample within the second audio waveform;
identifying a frequency of the audio sample; and
generating a frequency-dependent sample by applying frequency-dependent linear filtering to the audio sample, the frequency-dependent linear filtering simulating a frequency-dependent attenuation of the audio sample as the audio sample propagates through air.
6. The method of claim 1 , further including receiving the first audio waveform from a remote source.
7. The method of claim 1 , further including sending the simulated mixed output waveform to a remote physical audio listener location.
8. A system for simulating propagation and mixing of sounds in air, the system comprising:
a digital signal processing mixing simulation module, the simulation module configured to:
select a virtual source location within an audio interaction volume, the audio interaction volume associated with a first audio waveform, the first audio waveform including audio generated using a first audio isotropic source;
select an observation location corresponding to a virtual audio listener location; and
determine a second audio waveform using the first audio waveform, the second audio waveform including a plurality of simulated intermodulation products corresponding to the observation location; and
a summing amplifier module configured to generate an output audio waveform, the output audio waveform including the first audio waveform and the second audio waveform.
9. The system of claim 8 , the first audio waveform further including audio generated using a second audio isotropic source.
10. The system of claim 8 , further including a speaker, the speaker configured to transduce the output audio waveform into audible sounds.
11. The system of claim 8 , further including:
a first amplifier module configured to apply a first gain to the first audio waveform to generate a first amplified waveform; and
a second amplifier module configured to apply a second gain to the second audio waveform to generate a second amplified waveform;
wherein the summing amplifier module is configured to sum the first amplified waveform and the second amplified waveform to generate the output audio waveform.
12. The system of claim 8 , further including a frequency-dependent linear filter module, the frequency-dependent linear filter module configured to:
identify an audio sample within the second audio waveform;
determine a frequency of the audio sample; and
generate a frequency-dependent sample by applying frequency-dependent linear filtering to the audio sample, the frequency-dependent linear filtering simulating a frequency-dependent attenuation of the audio sample as the audio sample propagates through air.
13. The system of claim 8 , further including a communication module, the communication module configured to receive the first audio waveform from a remote source.
14. The system of claim 13 , the communication module further configured to send the output audio waveform to a remote physical audio listener location.