Disco was brand new then and there were a few jocks that had monstrous sound systems but they wouldn't dare play this kind of music. They would never play a record where only two minutes of the song was all it was worth. They wouldn't buy those types of records. The type of mixing that was out then was blending from one record to the next or waiting for the record to go off and wait for the jock to put the needle back on.
Herc really slipped up. With the monostrous power he had he couldn't mix too well. He was playing little breaks but it would sound so sloppy. I noticed that the mixer he was using was a GLI 3800. It was a very popular mixer at that time. It's a scarcity today but it's still one of the best mixers GLI ever made. At the time he wasn't using no cueing. In other words, the hole was there for a headphone to go in but I remember he never had headphones over his ears. All of a sudden, Herc had headphones but I guess he was so used to dropping the needle down by eyesight and trying to mix it that from the audio part of it he couldn't get into it too well.
Quoted in Rap Attack 2 (1991) by David Toop, p. 62
A scratch is nothing but the back-cueing that you hear in your ear before you push it out to the crowd. All you have to know is mathematically how many times to scratch it and when to let it go — when certain things will enhance the record you're listening to. For instance, if you're playing a record with drums--horns would sound nice to enhance it so you get a record with horns and slip it in at certain times.
Quoted in Rap Attack 2 (1991) by David Toop, p. 65