Hello, the unit you are thinking of was an 'ambience delay unit'. It came out in the late 70's and was manufactured by Koss, not Advent.
advent eq
looking for info on an eq unit that was put out by advent sometime in the 70's-80's.the system came with an eq unit and 2 small speakers.the eq unit had 4 or 5 settings.if i remember correctly some of the settings were like club setting,symphony hall,auditorium,etc any info i can get on this unit would be appreciated