5. DJ Hardware
Although Mixxx can be used with just a laptop or desktop computer, fully taking advantage of Mixxx's features requires specialized DJ hardware. Depending on your budget and application area, your setup and requirements may vary. This chapter provides general background information about various types of DJ hardware.
The Mixxx DJ Hardware Guide lists specific devices with information about their prices, features, and compatibility with Mixxx.
DJ controllers are devices with knobs, faders, buttons, and jog wheels to control DJ software such as Mixxx. Controllers allow quick access to different controls while providing tactile and visual feedback indicating the state of each control, such as the position of a knob or whether a switch is on or off. This allows you to focus on manipulating the music without needing to look at your computer screen all the time. Controllers also allow using two hands to manipulate two different controls at the same time, which is required for many mixing techniques.
DJ controllers typically do not do any actual audio processing. Instead, they send signals (typically MIDI or HID over a USB cable) to the computer to instruct DJ software how to manipulate the audio. Many DJ controllers include an audio interface with 2 separate stereo outputs built into the device. This allows the DJ to transport and setup only one piece of hardware in addition to a laptop. Some devices can be used as both a controller and hardware mixer.
Mixxx can work with any MIDI or HID controller as long as there is a mapping file to tell Mixxx how to understand the controller's signals. Mixxx comes bundled with a number of MIDI and HID mapping presets, which are listed in the Mixxx DJ Hardware Guide on the wiki. For controllers that Mixxx does not yet support, you can search the forum to see if anyone has started a mapping. You can also start one yourself using the information in the Controller Mapping Documentation on the wiki.
Using MIDI/HID Controllers describes how to configure Mixxx to use controllers.
5.2. Audio Interfaces
An audio interface (also known as a "sound card", although few of them are shaped like cards anymore) is a device that allows a computer to send output to and receive input from audio equipment. Whether using internal or external mixing, it is recommended to use a single audio interface with at least 4 independent output channels (2 separate stereo pairs).
The headphone jack on most laptops is not a second audio output. Rather, plugging headphones into the jack simply redirects the laptop's single stereo output from its speakers to your headphones. A splitter cable can be used to separate the stereo output of a headphone jack into two separate mono outputs for headphone cueing, but it is recommended to use a sound card with at least four mono outputs (for two stereo pairs). Such sound cards tend to be higher quality than those built into laptops and allow your mix to be enjoyed in stereo by your audience.
Unlike some proprietary DJ systems, Mixxx can use any audio interface and any MIDI or HID controller that your OS has drivers to use. If your controller has an integrated audio interface, you may choose to use a different audio interface for higher quality audio. Mixxx can also use multiple audio interfaces simultaneously.
5.2.1. Audio Interface Considerations
This section provides background information to help you choose an audio interface to use with Mixxx.
188.8.131.52. Bit Depth and Sample Rate
Most music is published with a bit depth of 16 bits at a sample rate of 44.1 kHz because this is all that is needed to store all the detail of music in digital form.
Bit depth determines the possible dynamic range of the signal. 16 bits is more than enough for playing back music. While 24 bits is helpful for recording, it is useless for playback.
Half the sample rate determines the maximum frequency that can be represented by the signal. Humans generally can't hear frequencies above 20 kHz, so a sampling rate of 44.1 kHz, representing a maximum frequency of 22.05 kHz, is fine for playback. Higher sample rates like 88.2 kHz and 96 kHz can be helpful to reduce aliasing distortion when recording, but have no benefit for playback and make your computer work harder.
For a more thorough and technical explanation of why 16 bits at 44.1 kHz is all that is needed for playback, read 24/192 Music Downloads Are Very Silly Indeed.
When considering specifications, higher dynamic range, higher signal-to-noise ratio (SNR), higher maximum output level, lower THD+N (Total Harmonic Distortion + Noise; look for a more negative dB value or smaller percentage), and lower crosstalk (more negative dB value) are better. Cheap audio interfaces tend to not have these specifications published.
184.108.40.206. Connector and Cable Types
If you are unfamiliar with professional audio equipment, read Digital DJ Tips' Essential Guide to Audio Cables for DJs to understand the different kinds of connectors on audio interfaces. It is better to use an audio interface with balanced outputs, especially if you will run long cables directly into an amplifier or active speakers without going through a hardware mixer. Balanced signals reject interference and are less susceptible to ground loop hum issues (which can be a problem when plugging unbalanced gear into separate power sources).
However, most venues have DJs plug into hardware DJ mixers, which typically only have RCA inputs (RCA cables cannot be balanced). Most home/computer speakers and amplifiers have RCA and/or 1/8" TRS stereo inputs. Most live sound mixers have balanced 1/4" TRS mono inputs. If you need to interconnect balanced and unbalanced gear, refer to this guide from Presonus (deleted, via archive.org) and this guide from Rane (deleted, via archive.org).
220.127.116.11. Number of Channels
Audio interfaces sometimes have multiple connectors for a single channel, resulting in more connectors than channels. So, not every connector can send or receive and independent signal. For example, some audio interfaces made for DJing have 4 output channels with 4 mono output connectors and 1 stereo headphone connector. This does not mean that the audio interface can send out 6 different signals at the same time; rather, the signal on 2 of the mono outputs and the stereo headphone output would be the same. Also, many controllers have separate master and booth outputs with independent volume controls, but they both play the same signal.
18.104.22.168. Vinyl Control and Phono Preamplifiers
Turntables output low voltage (phono level) signals that need to be amplified to line level before most audio equipment can work with them. So, if you want to use Vinyl Control, sometimes referred to as a Digital Vinyl System (DVS), it is best to have phono preamplifiers (one for each deck) somewhere between your turntable and sound card to boost the turntable's phono level signal to line level. Mixxx can amplify phono level signals in software, but it is better to do it in hardware. The phono preamp can be in the turntable, in the audio interface, or a stand alone device. Most audio interfaces do not have phono preamps; these are generally found on audio interfaces specifically made for controlling DJ software with timecode vinyl. Mixers with audio interfaces have phono preamps on their deck inputs, but not necessarily on every deck input. Many higher-end all-in-one controllers also include audio interfaces with phono preamps.
Mixers are devices that combine audio signals. DJ mixers are different from live and studio mixers because they have multiple stereo channels with phono preamplifiers for connecting Turntables. It is conventional to use a DJ mixer with Vinyl Control, but vinyl control can be used without a hardware mixer.
Using Mixxx with a DJ mixer requires an audio interface with at least 4 mono outputs (2 stereo pairs) to send Mixxx's decks to the mixer's stereo channels. Some DJ mixers have a USB audio interface built into them. This lets Mixxx send unmixed audio files directly to the mixer without needing a separate stand-alone audio interface.
Often DJs who use DJ software with internal mixing send their master output to a hardware mixer. This can be helpful to send the mixed signal to both a main speaker output for the audience and booth speakers for the DJ with separate gain controls for each output. It also facilitates smooth transitions between DJs.
However, using an external mixer with internal mixing is not necessary and reduces the sound quality. Each piece of equipment an audio signal passes through reduces the sound quality, so avoiding unnecessary equipment in the signal path can provide better sound quality. Many DJ controllers provide separate master and booth outputs with independent volume controls. Alternatively, a sound card with at least 6 output channels can be used with Mixxx's Booth output.
Many people confuse "analog mixers" and "hardware mixers", but these are not the same. Many hardware mixers process audio digitally with specialized signal processors as opposed to a general purpose CPU like those in laptop and desktop computers.
Turntables are mechanical devices that play music recordings cut into vinyl phonograph records. Before software like Mixxx was available, the art of DJing originated with turntables and DJ mixers. Special vinyl records can be used with turntables to control the playback of digital files in Mixxx as if the digital file was pressed onto the vinyl record.
CDJs are devices that play digital audio files and have controls from manipulating the playback of the audio. Originally CDJs played audio CDs, but new devices typically use USB storage drives or SD cards. Some CDJs can be plugged into a computer with a USB cable to function as a controller for Mixxx.
Microphones convert changes in sound pressure in air to changes in voltage (an analog audio signal). Mixxx can work with any microphone that can be plugged into your audio interface.