Adaptive diffuse signal generation in an upmixer
An audio processing system, such as an upmixer, may be capable of separating diffuse and non-diffuse portions of N input audio signals. The upmixer may be capable of detecting instances of transient audio signal conditions. During instances of transient audio signal conditions, the up-mixer may be capable of adding a signal-adaptive control to a diffuse signal expansion process in which M audio signals are output. The upmixer may vary the diffuse signal expansion process over time such that during instances of transient audio signal conditions the diffuse portions of audio signals may be distributed substantially only to output channels spatially close to the input channels. During instances of non-transient audio signal conditions, the diffuse portions of audio signals may be distributed in a substantially uniform manner.
1. A method for deriving M diffuse audio signals from N audio signals for presentation of a diffuse sound field, wherein M is greater than N and is greater than 2, and wherein the method comprises:
receiving the N audio signals, wherein each of the N audio signals corresponds to a spatial location;
deriving diffuse portions of the N audio signals;
detecting instances of transient audio signal conditions; and
processing the diffuse portions of the N audio signals to derive the M diffuse audio signals, wherein during instances of transient audio signal conditions the processing comprises distributing the diffuse portions of the N audio signals in greater proportion to one or more of the M diffuse audio signals corresponding to spatial locations relatively nearer to the spatial locations of the N audio signals and in lesser proportion to one or more of the M diffuse audio signals corresponding to spatial locations relatively further from the spatial locations of the N audio signals.
2. The method of claim 1 , further comprising detecting instances of non-transient audio signal conditions, wherein during instances of non-transient audio signal conditions the processing involves distributing the diffuse portions of the N audio signals to the M diffuse audio signals in a substantially uniform manner.
3. The method of claim 2 , wherein the processing involves applying a mixing matrix to the diffuse portions of the N audio signals to derive the M diffuse audio signals.
4. The method of claim 3 , wherein the mixing matrix is a variable distribution matrix that is derived from a non-transient matrix more suitable for use during non-transient audio signal conditions and a transient matrix more suitable for use during transient audio signal conditions.
5. The method of claim 4 , further comprising determining a transient control signal value, wherein the variable distribution matrix is derived by interpolating between the transient matrix and the non-transient matrix based, at least in part, on the transient control signal value.
6. The method of claim 5 , wherein the transient control signal value is time-varying, can vary in a continuous manner from a minimum to a maximum value, or can vary in a range of discrete values from a minimum value to a maximum value.
7. The method of claim 5 , further comprising deriving the transient control signal value in response to the N audio signals; and/or
wherein determining the variable distribution matrix involves computing the variable distribution matrix according to the transient control signal value, or retrieving a stored variable distribution matrix from a memory device.
8. The method of claim 1 , wherein the method further comprises:
deriving K intermediate signals from the diffuse portions of the N audio signals such that each intermediate audio signal is psychoacoustically decorrelated with the diffuse portions of the N audio signals and, if K is greater than one, is psychoacoustically decorrelated with all other intermediate audio signals, wherein K is greater than or equal to one and is less than or equal to M−N.
9. The method of claim 8 , wherein deriving the K intermediate signals involves a decorrelation process that includes one or more of delays, all-pass filters, pseudo-random filters or reverberation algorithms, and/or wherein the M diffuse audio signals are derived in response to the K intermediate signals as well as the N diffuse signals.
10. An apparatus, comprising:
an interface system; and
a logic system capable of:
receiving, via the interface system, N input audio signals, wherein each of the N audio signals corresponds to a spatial location;
deriving diffuse portions of the N audio signals;
detecting instances of transient audio signal conditions; and
processing the diffuse portions of the N audio signals to derive M diffuse audio signals, wherein M is greater than N and is greater than 2, and wherein during instances of transient audio signal conditions the processing comprises distributing the diffuse portions of the N audio signals in greater proportion to one or more of the M diffuse audio signals corresponding to spatial locations relatively nearer to the spatial locations of the N audio signals and in lesser proportion to one or more of the M diffuse audio signals corresponding to spatial locations relatively further from the spatial locations of the N audio signals.
11. The apparatus of claim 10 , wherein the logic system is capable of detecting instances of non-transient audio signal conditions and wherein during instances of non-transient audio signal conditions the processing involves distributing the diffuse portions of the N audio signals to the M diffuse audio signals in a substantially uniform manner.
12. The apparatus of claim 11 , wherein the processing involves applying a mixing matrix to the diffuse portions of the N audio signals to derive the M diffuse audio signals.
13. The apparatus of claim 12 , wherein the mixing matrix is a variable distribution matrix that is derived from a non-transient matrix more suitable for use during non-transient audio signal conditions and a transient matrix more suitable for use during transient audio signal conditions.
14. The apparatus of claim 13 , wherein the transient matrix is derived from the non-transient matrix.
15. The apparatus of claim 14 , wherein each element of the transient matrix represents a scaling of a corresponding non-transient matrix element.
16. The apparatus of claim 15 , wherein the scaling is a function of a relationship between an input channel location and an output channel location.
17. The apparatus of claim 13 , wherein the logic system is capable of determining a transient control signal value, wherein the variable distribution matrix is derived by interpolating between the transient matrix and the non-transient matrix based, at least in part, on the transient control signal value.
18. The apparatus of claim 10 , wherein the logic system is capable of:
transforming each of the N audio signals into B frequency bands; and
performing the deriving, detecting and processing separately for each of the B frequency bands.
19. The apparatus of claim 10 , wherein the logic system is capable of:
panning non-diffuse portions of the N input audio signals to form M non-diffuse audio signals; and
combining the M diffuse audio signals with the M non-diffuse audio signals to form M output audio signals.
20. A non-transitory medium having software stored thereon, the software including instructions for controlling at least one apparatus to:
receive N input audio signals, wherein each of the N audio signals corresponds to a spatial location;
derive diffuse portions of the N audio signals;
detect instances of transient audio signal conditions; and
process the diffuse portions of the N audio signals to derive M diffuse audio signals, wherein M is greater than N and is greater than 2, and wherein during instances of transient audio signal conditions the processing comprises distributing the diffuse portions of the N audio signals in greater proportion to one or more of the M diffuse audio signals corresponding to spatial locations relatively nearer to the spatial locations of the N audio signals and in lesser proportion to one or more of the M diffuse audio signals corresponding to spatial locations relatively further from the spatial locations of the N audio signals.