Matrix decoder with constant-power pairwise panning
View Patent ↗A constant-power pairwise panning upmixing system and method for upmixing from a two-channel stereo signal to a multi-channel surround sound (having more than two channels). Each output channel is some combination of the two input channels. Closed-form solutions are used to calculate dematrixing coefficients that are used to weight each input channel. The dematrixing coefficients are computed based on an inter-channel level difference and an inter-channel phase difference between the two input signals. The weighted input channels then are mixed uniquely for each output channel to generate a surround sound output from the stereo input signal. Each dematrixing coefficient has an in-phase component and an out-of-phase component. The phase coefficients for each component vary in time and are based on the phase difference between the input signals. The resultant surround sound output faithfully simulates the audio content as originally mixed.
1. A method for upmixing a two-channel input audio signal, comprising:
calculating an inter-channel level difference between a first channel and a second channel of the two-channel input audio signal;
calculating an inter-channel phase difference between the first and second channels;
calculating a first dematrixing coefficient based on the inter-channel level difference and the inter-channel phase difference;
calculating a second dematrixing coefficient based on the inter-channel level difference and the inter-channel phase difference;
calculating a third dematrixing coefficient using the inter-channel phase difference and phase coefficients that include an in-phase coefficient and an out-of-phase coefficient;
generating at least one additional output channel using the third dematrixing coefficient;
generating a channel of an upmixed multi-channel output audio signal by summing the first channel multiplied by the first dematrixing coefficient with the second channel multiplied by the second dematrixing coefficient and adding the at least one additional output channel to the upmixed multi-channel output audio signal; and
outputting the channel of the upmixed multi-channel output audio signal for playback through one or more playback devices.
2. The method of claim 1 , further comprising calculating the inter-channel level difference for the two-channel input audio signal as a ratio of a left channel and a sum of the left channel and a right channel.
3. The method of claim 2 , wherein calculating the inter-channel level difference, denoted as ICLD, further comprises using the equation:
ICLD
=
L
2
L
2
+
R
2
where L is the left channel and R is the right channel.
4. The method of claim 1 , wherein calculating the first and second dematrixing coefficients further comprises calculating an estimated panning angle, denoted as {circumflex over (θ)}, based on the inter-channel level difference, wherein the estimated panning angle is an estimate of an original panning angle associated with the two-channel input audio signal.
5. The method of claim 4 , wherein calculating the estimated panning angle further comprises using the equation (where the inter-channel level difference is denoted as ICLD):
θ
^
=
2
·
cos
-
1
(
ICLD
)
π
6. The method of claim 4 , wherein calculating the first and second dematrixing coefficients further comprises:
calculating an in-phase coefficient and an out-of-phase coefficient based on the estimated panning angle; and
calculating the first and second dematrixing coefficients based on the inter-channel phase difference, the in-phase coefficient, and the out-of-phase coefficient.
7. The method of claim 1 , wherein calculating the first and second dematrixing coefficients further comprises:
determining the inter-channel phase difference, denoted as ICPD, between the first and the second channels based on the equation:
ICPD
=
Re
{
Σ
L
·
R
*
}
Σ
L
2
∑
R
2
where * denotes complex conjugation, L is the first channel, and R is the second channel and wherein the inter-channel phase difference indicates whether the first channel is in phase or out of phase with the second channel at a given time.
8. A method for upmixing a two-channel input audio signal having a first input channel and a second input channel into an upmixed multi-channel output audio signal having greater than two channels, comprising:
calculating an inter-channel level difference between the first input channel and the second input channel;
calculating an inter-channel phase difference between the first input channel and the second input channel;
calculating an in-phase coefficient and an out-of-phase coefficient based on the inter-channel level difference;
calculating a first dematrixing coefficient based on the in-phase coefficient and the out-of-phase coefficient;
calculating a second dematrixing coefficient based on the in-phase coefficient and the out-of-phase coefficient;
multiplying the first input channel by the first dematrixing coefficient to generate a first sub-signal and the second input channel by the second dematrixing coefficient to generate a second sub-signal;
calculating a third dematrixing coefficient using the inter-channel phase difference and phase coefficients that include the in-phase coefficient and the out-of-phase coefficient;
generating at least one additional output channel using the third dematrixing coefficient;
mixing the at least one additional output channel, the first sub-signal and the second sub-signal to generate the upmixed multi-channel output audio signal for playback; and
outputting the upmixed multi-channel output audio signal for playback through one or more playback devices.
9. The method of claim 8 , wherein the first dematrixing coefficient is a combination of the in-phase coefficient and the out-of-phase coefficient based on the inter-channel phase difference.
10. The method of claim 9 , wherein the second dematrixing coefficient is a combination of the in-phase coefficient and the out-of-phase coefficient based on the inter-channel phase difference.