Digital Streaming Glossary
To make sense of the jargon used, we have compiled a brief Digital Streaming Glossary to help you find your way around the terms used:
AAC (Advanced Audio Coding)
This is a lossy coding format for audio – it is generally thought of as offering higher rates of compression with better audio quality than MP3. It is used widely in iTunes and also on the Playstation 3. – File extensions associated with AAC include aac, m4a, mp4, m4p, 3gp
ADSL (Asynchronous Digital Subscriber Line)
This is the technology most commonly used to send broadband data over a telephone line. The speed the data goes at is dependent on the distance from the ADSL modem in the house to the subscriber line multiplexer in the telephone exchange. The Asynchronous bit of the name refers to the fact that data goes from the Internet to the subscriber much faster than from the subscriber to the internet.
AIFF (Audio Interchange File Format)
This is a file format originally created by Apple to store MIDI (Musical Instrument Digital Interface) information. It stores music in a similar way to WAV files and is common on both windows based computers and Apple MACs
ALAC (Apple Lossless Audio Codec)
This is a format that Apple created for storing audio in a format that allows the original data to be exactly re-created, it is used in iTunes. File extensions associated with ALAC include m4a (similar to AAC but lossless).
This refers to the number of bits per second that are transmitted when sending (streaming) data. The data is formed of data words, where each word is made up of a number of bits. The data word size is dependent on how the music was digitised in the first place. 16bit and 24bit word lengths are common – the larger the word length, the greater definition (loudest to quietest change) is available within the music.
Music streamed over a network is split into small packets of data that are then sent out. The data packets may take different amounts of time to reach the player at the other end, and so are stored in a buffer to make sure that they can be re-assembled in the correct order, and that there is a constant stream of data packets available to the digital to analogue converter, even if there is a small gap in the stream of data packets arriving.
The CODEC is a software program that is typically embedded within other programs and allows the conversion and playback between different music coding formats,
When music is converted from the original analogue data into a digital file, there are techniques that are used to squash the size of that file into a manageable size. Generally there is a trade-off between how small the file can be, and how much damage is done to the original music quality. Compression can be lossy where the trade-off is that bits of the music get left off the more it is compressed i.e. it is impossible to re-create the exact original sound wave. Whereas Lossless compression makes the file small, however allowing the original waveform to be exactly recreated again. Here the smaller the file size the more processing that is required to re-create the original file.
The control point in a digital streaming system is the human interface device where you physically control what the system is playing. It is typically a computer, iPhone or iPad, however some players have a control point built into them so you can control it from the front panel.
When one track ends and a new one starts in a play list, there is normally a gap between tracks. With crossfading the next track is started playing before the first one has completely finished, so the music then fades from one directly into the other. Not all players can do this.
DAP (Digital Audio Player)
The piece of equipment that connects to a data network and can receive a digital audio stream and convert this into an analogue music signal is referred to as a Digital Audio Player or Render.
DRM (Digital Rights Management)
DRM is an encryption algorithm developed by Microsoft and others, to prevent Music being played on anything apart from authorised machines. When a user tries to play the file, their license is checked in order the play the file.
A firewall is a piece of software or hardware (or both) that checks the communications going in and out of a computer. It is designed to prevent unauthorised access (typically) from the internet to your computer, however may stop your computer from communicating with other devices unless they are on the firewall allowed list – This may or may not happen automatically.
FLAC (Free Lossless Audio Codec)
This music file compression format is widely used as it is an open standard. It can cope with a variety of music resolutions including Studio Master Quality, and also has the ability to include Metadata details within the file. Due to the open nature, it is widely used and most digital music players will play FLAC files.
HDMI (High Definition Multimedia Interface)
HDMI is an interface for audio, video and data using a single cable. It was first developed in 2002, and was intended to be a single standard that would allow multimedia devices to be connected together. It is now widely used as a (primarily) video interface to displays, however recent innovations include the ability to transmit internet data and return audio (e.g. from a TV back to the amplifier). It is highly useful interface, however care has to be used especially when using long cable runs.
Every device connected and talking to a data network has to be uniquely identified on that network. If the network is using Internet Protocol (and most do now), then this unique address is known as the IP Address. The address is usually allocated automatically by the router in the network – most commonly in home networks this is the Broadband Router. Sometimes it is useful to fix the IP address, so that it can never change in the network (e.g. after a power failure).
In a digital system, the words used to represent the various sampled analogue levels of a music waveform should occur in regular time intervals. The clocks used to generate these timing intervals are generally extremely accurate, however there is usually a very small time difference between the gaps between these samples, and this difference is known as jitter. If you count 1000 samples over a 1 second period, you could call the sample rate 1 kilo samples per second, however the samples could change rate through that one second, so you could still count 1000 samples, however the gap between samples would not necessarily be even. This jitter means that when you are replaying a digital music signal, it causes slight distortions into the waveform that is re-generated compared to the original. This is why in studios a far higher sample rate is used than is technically necessary, as it radically reduces the distortion effects caused by clock jitter, and why the higher data rates sound better.
LAN (Local Area Network)
Most home computer networks are formed by devices connecting to the broadband router either by being physically plugged into the back via Ethernet cable, or by being logged on via WiFi. The complete set of devices connected to the router and able to talk to each other is referred to as the Local Area Network. Outside the router towards the Internet is referred to as the Wide Area network (WAN).
When data is transmitted across a network, it takes a small amount of time, and this is usually referred to as the latency. Often the latency also includes processing time. Many satellite receivers include Lip Sync delays so that the sound can be delayed to match the processing latency of the video when it is transmitted over the Satellite broadcast system.
Lossy / Lossless compression
Compression of an audio file can be at the expense of some of the original data and is called lossy compression. Where the file is compressed but can be perfectly recovered to the original data, it is called lossless.
A Media player is a generic description for a piece of equipment that can play digital music or video.
When a piece of music is converted into a data file, additional information is required to identify the music, artist, album etc. This additional information is the Meta Data. Some formats (e.g. FLAC) can embed this meta data into the file itself, however other formats have to rely on the filename, or a separate meta data file to provide this information.
Previously known as MPEG-1 layer 3, this is a lossy compression format, and is widely used. An MP3 player has come to be a generic term for any digital music player.
MPEG (Moving Picture Experts Group)
MPEG is generally used as an abbreviation for a lossy compression format for audio and video files. There are different versions of MPEG compression: (MPEG-1, MPEG-2, MPEG-4 etc).
When a source of digital music streaming is streaming music data, it can either send this data to a specific device (Unicast), or it can broadcast the data stream so multiple devices can pick it up simultaneously. Multicast increases the resources required on the network, so some care has to be exercised when using multicast.
The Network Attached Storage (NAS) Drive is a device that is connected to the local area network, and includes a large storage disc where the digital Music and videos are stored. Many include media streaming software so that they can send the data to the players.
Any Digital devices that are connected together form a network. It can be as simple as two devices, or it can contain many hundreds of devices.
Ogg is a file container format that is normally associated with the Vorbis audio compression Codec, the resultant called Ogg Vorbis. The Vorbis compression format is a lossy compression named after one of Terry Pratchet’s characters from his Discworld series of novels.
Quicktime is a software multimedia architecture created by Apple to play Music and Video. It is included in the Apple operating system and can be downloaded to play files in the Windows environment.
A Renderer is a generic term for any device that can take digital data and present it for playback. In the Digital Music Streaming world, it usually refers to the Media Player or Digital Audio Player.
The act of taking the music data from a CD and storing it as a file in a computer environment is called ripping. There are a number of low cost or free programs that will do this with varying degrees of quality. The higher quality ripping programs will error check and compare rips from other machines across the Internet, for high confidence in the resultant file.
A router in a network issues IP addresses to connected devices, and routes data to and from the Internet. It often includes other functions such as ADSL Modem, and WiFi Access point.
RTSP (Real Time Streaming Protocol)
The Real Time Streaming Protocol is used over networks to control real time streaming of video and audio data.
Scrobbling is a term invented by the music service LastFM, whereby the system retains data about the music you listen to. This data is then used for music playing statistics and for suggesting alternative music you might like to hear.
A server is a generic name for a computer that serves data to other computers. In the Digital Music Streaming world, it refers to a small computer (e.g. NAS Drive) and streaming software that sends the music data to one or more music renderers or players.
Digital Streaming sends a stream of music data to a playback device rather than a complete file. The stream can be started and stopped, and can start playing before the end of the file is reached.
WAV (Waveform Audio)
The WAV format (named after the file extension .wav) is commonly used in the Windows environment for uncompressed audio files. It can include a number of codecs but most commonly uses the Linear Pulse Code Modulation (LPCM) format as used on CDs at two channels of 16bit words and a 44.1KHz sample rate. WAV files are often large, however are frequently used in time critical applications (such as music editing) as they are easier to manipulate in software. WAV is capable of having embedded metadata, but this is seldom used as many devices don’t recognise it.
WMA (Windows Media Audio)
WMA is an audio compression format developed by Microsoft. It is a proprietory technology that is embedded in the Windows operating system, and has four different codecs including the capability for high resolution and multi-channel audio.