This technique involves cutting the the frequency in a song. This is assuming you have a DJ mixer that has bass, mid range, and treble. Normally, cutting the bass or treble will produce an effect that sounds as if the bass just stopped or sounds as if the song is gradually getting louder even though you haven't touched the volume, depending on how fast the frequency is introduced into the song.
There's a practical side to using this technique. One is that if two songs are being beat mixed with bass lines that are very different from one another, cutting one will make the transition smoother.
This technique sounds as if one track suddenly winds down and segues right into the next beat. To execute this technique, beat match two tracks. On the last bar of track 1 (right before track 2 comes in), stop track 1 and sharply spin it backwards while simultaneously flipping the crossfader so that track 2 comes in on the final beat. This is a little tricky and takes some practice.
This is similar to the spinback, but instead of reversing the record by spinning it backward, you push the stop button. To pull this off, you have to know the how long it takes for your deck to stop spinning. When it does, snap the crossfader to deck 2, which should come in right on the beat.
There are many different scratching techniques DJs use. These are just the tip of the iceberg.
The scribble is a normal-timed scratch that's tripled or quadrupled in timing by a quicker forward and backward motion of the fingers and wrist. The echo fade involves playing the same scratch over and over while working the volume fader back and forth making it sound like an echo. The transform echo fade is the same except you use a scribble-type motion on the fader.
Creating music for film and television is a whole different beast. The music and audio is in your face, mixed at the same levels. In the case of movie-trailer music, it must be created to sound similar to the movie music being normally created before the movie is released and sometimes before it's finished shooting.
Mic placement and choice is important at the source when recording sound for mixing and design. Planning ahead and taking into account the recording space has a tremendous impact on the final sound.