Haeco-CSG

The Haeco-CSG or Holzer Audio Engineering-Compatible Stereo Generator system was an analog electronic device developed by Howard Holzer, Chief Engineer at A&M Records in Hollywood, California.

His company, Holzer Audio Engineering, developed the system in the 1960s during the years of transition from mono to stereophonic sound in popular music recording. The process was used primarily from about 1968 until 1970 but still exists on a significant number of recordings made during the time.

The Haeco-CSG process was designed to make stereophonic vinyl LP records compatible with mono playback equipment. These recordings were intended to make the 2 channel stereo mix to automatically "fold-down" properly to a single mono channel.

The reason for the process is the compatibility issue between stereophonic and monaural recordings: information which is identical on both the left and right channels of a stereophonic mix sounds too loud when played back on mono AM and FM radio stations and phonographs. When the left and right channels are summed together, any musical parts that are common to both channels combine to be 6 decibels louder than they are in the same mix when played in stereo. Vocals, solo instruments and bass lines are often mixed equally to both stereo channels — these sounds tend to be too loud when heard in mono.

Due to technical issues in the record playback process the practice of creating separate mono and stereo mixes of the same record was common during the 1960s. This also required manufacturing and distributing mono and stereo versions of the same album title. The Haeco-CSG system appeared to be an attractive option for record companies and retailers by allowing them to cut costs. Engineers could produce a single mix, record companies could manufacture and distribute one version, and vendors could stock one product.

Haeco-CSG technology works on the basis of phase cancellation. When two waves that are not in phase are mixed, the resulting waveform has an attenuation in accordance to the degree of shift. For example, two waves which are 180 degrees out of phase will entirely cancel out when mixed together whereas two waves which are entirely in phase will double in amplitude. A difference in phase between 180 and 0 degrees results in a partial cancellation, which is the effect Haeco-CSG takes advantage of.

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