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Automatic Monitor Mixing for Live Musical Performance

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During live performances musicians require a monitor mix on stage in order to hear themselves and others. The monitor mix is usually controlled by a set of monitor loudspeakers that face away from the audience. These require their own mixing, separate from the audience feed. An automated mixing algorithm can approach the results of an expert mixer for the monitor function. A model has been developed that describes the basis for this monitoring function while incorporating minimum and maximum sound intensity. The solution space is constrained by the need to avoid feedback, and this limits the degree to which the monitor mix can achieve the target requirements. However, the algorithm suggests optimal location of monitors and direct sources (such as guitar amplifiers) on stage.

JAES Volume 57 Issue 11 pp. 927-936; November 2009
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Andrew J. Horsburgh

Comment posted December 8, 2009 @ 16:23:42 UTC (Comment permalink)

I read this paper with great anticipation to see what advancements are being made in regards to stage sound and primarily ones which involve the, now ever common, digital live music industry.
I have read this paper several times and I find there to be several large issues that appear in the "idea" of automatic monitor mixing. All of the information written has been created from my point as a live engineer working in popular modern music venue.

Firstly, the artists generally require a much different mix than a FOH mix. Most artists will require a large percentage of themselves, and the instrument they use as a timing aide (either kick or vocals in most cases). How would this practice be over come in an automated system?

Second, the diagram of the stage - which I understand is there for purely theoretical values to ensure the best practice of this procedure are about 5-10 years out of date in practice. There are many bands, managers and engineers who have accepted the "look" of guitar and bass amps being in line with the downstage edge of the drum riser. A change in this would probably cause a large number of bands to have difficulty accepting and adjusting to the new way of "mixing" their wedges with the back line. The second diagram which is a more suitable stage setup is one which many older bands adopt (bass amp facing the drummer) is albeit an older style is still used in practice. A point to note is that this is certainly in the >5% of bands who use the technique they are also bands whom require a lesser monitor rig or refuse monitors at all.

The last point to make is regarding the acoustical properties of the instruments themselves in a monitor situation. Many of the large venues, and monitor engineers that still utilize the conventional "wedge" approach of engineering use EQ on each of the signals to have their most prominent characteristics cut through the rest of the mix. This is appropriate in many cases due to the artists requirement to hear their main timing aide without outrageous SPL levels. For example the kick will have a greater click content, with very little sub, so that the bass player and drummer can hear their instrument over the stage noise.
In shows where there happens to be either a singer or the band are on In Ear Monitors (IEMs) there is also a reoccurring practice of facing amplifiers towards the rear of the stage. IEMs are now becoming very common in much larger shows and "reversing" the amplifiers also aides the monitor engineer in satisfying the amount of artist required in their "ears". This combined with the carving of the signals in the traditional wedges means that I cannot see a way that either spectral nor any other automated system can be produced to satisfy the needs of modern productions.

I have also neglected to mention the idea of having an SPL-related mix, while this maybe accurate for some artists it is also common to find vastly different SPLs on stage each night with each band / group member. Also there is common place for the stage sound to be equal to the floor sound in pressure level. A recent update by one band online stated that they tripped a 103dB limiter on stage in France throughout their show. In the venues which they are playing (300-500 cap.) I doubt that the FOH sound will be able to cleanly deliver a flat level above this in these size venues, I may be wrong however!

As the paper states at the end, much more research is required into this field - but I think that although there is promise in the idea, and the theory is obviously being fledged out however there seems to be a few points which need to be addressed before this system can be accepted by the Professional Monitor Engineers that I have spoken with.

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