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A real-time semi-autonomous audio panning system for music mixing

Enrique Perez Gonzalez and Joshua D. Reiss

A real-time semi-autonomous stereo panning system for music mixing has been implemented. The system uses spectral decomposition, constraint rules and cross-adaptive algorithms to perform real-time placement of sources in a stereo mix. A subjective evaluation test was devised to evaluate its quality against human panning. It was shown that the automatic panning technique performed better than a non-expert and showed no significant statistical difference to the performance of a professional mixing engineer.

Demonstration videos

Autopanner Automatic panner- A video of an 8 channel mix automatically panned with no human intervention

In order to evaluate the performance of the semi-autonomous panner algorithm against human performance, a double blind test was designed. Both auto-panning algorithms were tested, the band-pass filter classifier known as algorithm type A, and the low-pass classifier known as algorithm type B. Algorithms were randomly tested in a double blind fashion. The control group consisted of three professional human experts and one non-expert, who had never panned music before. The test material consisted of 12 multi-track songs of different styles of music. Stereo sources were used in the form of two separate mono tracks. Where acoustic drums were used they would be recorded with multiple microphones and then pre-mixed down into a stereo mix. Humans and algorithms used the same stereo drum and keyboard tracks as separate left and right mono files. All 12 songs were panned by the expert human mixers and by the non-expert human mixer. They were asked to pan the song while listening for the first time. They had the length of the song to determine their definitive panning positions. The same songs were passed through algorithms A and B only once for the entire length of the song. Although the goal was to give the human and machine mixers as close to the same information as possible, human mixers had the advantage of knowing which type of instrument it was. Therefore, they assigned priority according to this prior known knowledge. For this reason a similar priority scheme was chosen to compensate for this. Both A and B algorithms used the same priority schema.

Panning test interface

The test used two questions to measure the perceived overall quality of the panning for each audio comparison. For the first question, ‘how different is the panning of A compared to B?’, a continuous slider with extremities marked ‘exactly the same’ and ‘completely different’ was used. The answer obtained in this question was used as a weighting factor in order to decide the validity of the next question. The second question, ‘which file, A or B, has better panning?’, used a continuous slider with extremes marked ‘A quality is ideal’ and, ‘B quality is ideal’. For both of these questions, no visible scale was added in order not to influence their decision. The test subjects were also provided with a comment box that was used for them to justify their answers to the previous two questions. During the test it was observed that expert subjects tend to use the name of the instrument to influence their panning decisions. In other words they would look for the “bass” label to make sure they kept it center. This was an encouraging sign that panning amongst professionals follows constraint rules similar to those that were implemented in the algorithms.

Sample data

Expert 1
Expert 2
Expert 3
Nonexpert
Algorithm A
Algorithm B

Publications

Enrique Perez Gonzalez and J. D. Reiss, "Automatic equalization of multi-channel audio using cross-adaptive methods", Proceedings of the 127th AES Convention, New York, October 2009

Enrique Perez Gonzalez, Josh Reiss "Automatic Gain and Fader Control For Live Mixing", IEEE Workshop on Applications of Signal Processing to Audio and Acoustics (WASPAA), New Paltz, New York, October 18-21, 2009

Enrique Perez Gonzalez, Josh Reiss "Determination and correction of individual channel time offsets for signals involved in an audio mixture", 125th AES Convention, San Francisco, USA, October 2008

Enrique Perez Gonzalez, Josh Reiss, "Improved control for selective minimization of masking using interchannel dependency effects", 11th International Conference on Digital Audio Effects (DAFx), September 2008

E. Perez_Gonzalez and J. Reiss, "An automatic gain normalisation technique with applications to audio mixing", Proceedings of the Audio Engineering Society 124th Convention Amsterdam, The Netherlands, 2008.

E. Perez_Gonzalez and J. Reiss, "Automatic mixing: live downmixing stereo panner", In Proceedings of DAFx-07, Bordeaux, France, 2007.

Enrique Perez Gonzalez and Joshua D. Reiss, "Anti-feedback device," UK patent GB0808646.4, filed June 13, 2008