Beatmixing is a disk jockey technique of mixing two tracks so that the beats of one occur at the same time as the other.
Beatmixing was invented in the late 1960s by Francis Grasso, who tried to keep people from leaving the dance floor between the songs. Initially he was looking for records with the same tempo, counting the tempo with a metronome. When the tempos didn't match, he was adjusting the pitch control on the turntable to bring the beats in sync. Rosie, a mixer built for him by Alex Rosner, let him listen to any channel in the headphones independently of what was playing on the speakers, allowing him to beatmatch the records by ear; this became the defining feature of DJ mixers.
These days beatmatching and beatmixing are considered basic techniques among DJs in electronic dance music genres, and it's standard practice in clubs to keep the constant beat through the night, even if DJs change in the middle.
The beatmixing technique consists of the following steps:
1. While a record is playing, beatmatch a new record to it, using headphones for monitoring. Use gain (or trim) control on the mixer to match the levels of the two records.
2. Restart and slip-cue the new record at the right time. Pay attention to track structures; careful phrasing can make the mix seamless.
3. Before fading in the new track, check that the beats of two tracks match by listening to both channels together in the headphones, as the sound from the speakers can reach you with a delay.
4. Gradually, fade in parts of the new track while fading out the old track. While in the mix, ensure that the tracks are still synchronized, adjusting the records if needed.
Pitch and tempo
The pitch and tempo of a track are normally linked together: spin a disc 5% faster and both pitch and tempo will be 5% higher. However, some modern DJ software can change pitch and tempo independently using time-stretching and pitch-shifting, allowing harmonic mixing. This technique is referred to as beatmatching.
Beatmix or beatmixing however should not be confused with another term used in radio imaging. Radio imaging refers to any produced audio material sung or voice over used to identify a radio station. A radio imaging company in Seattle, Washington called ReelWorld used the term "beatmix" to refer to a type of imaging material in which a jingle, a voice over liner and audio clips are produced to blend on a song intro. The concept is still the same with DJ beatmixing.
An electronic mixer is a device that combines two or more electronic signals into one composite output signal. There are two basic types of mixer. Additive mixers add two signals together, and are used for such applications as audio mixing. Multiplying mixers multiply the signals together, and produce an output containing both original signals, and new signals that have the sum and difference of the frequency of the original signals.
 Additive mixers
Additive mixers add two or more signals, outputting a composite signal that contains the frequency components of each of the source signals. The simplest additive mixers are simple resistor networks, and thus purely passive, while more complex mixers employ active components such as buffer amplifiers for impedance matching and better isolation.
 Product Mixers
Ideal product mixers act as signal multipliers, producing an output signal equal to the product of the two input signals. Product mixers are often used in conjugation with an oscillator in the communications field to modulate signal frequencies. Product mixers can either up-convert or down-convert an input signal frequency, but it is more common to down-convert to a lower frequency to allow for easier filter design. In many typical circuits, the single output signal actually contains multiple waveforms, namely those at the sum and difference of the two input frequencies and harmonic waveforms. The ideal signal may be obtained by removing the other signal components with a filter.
Product mixers have been implemented in a wide variety of ways. The most popular are Gilbert cell mixers, diode mixers, diode ring mixers (ring modulation) and switching mixers. A diode mixer has two or more signals going into a diode. Diodes mixers take advantage of the non-linearity of diode devices to produce the desired multiplication in the squared term. It is a very inefficient method as most of the power output is in other unwanted terms which need filtering out. Inexpensive AM radios still use diode mixers.
Gilbert cell mixers are just an arrangement of transistors that multiplies the two signals. The switching mixers (below) pass more power and usually insert less distortion.
Switching mixers use an array of Field effect transistors or (in older days) vacuum tubes. These are used as electronic switches, to permit the signal to go one direction, then the other. They are controlled by the signal being mixed. They are especially popular with digitally-controlled radios.