Music
There has long been technology for listening to and creating music from vinyl records, cassette tapes to CDs.
It was CDs (Compact Disc) that introduced digital recording to consumer products. Previous technologies used analogue techniques.
CDs are able to preserve the range of loudness (dynamic range) and tonal range (frequency range) to fairly accurately reproduce normal musical sounds. However this creates a lot of digital data which some modern technologies have reduced by 'compression' methods.
The reduction in the amount of digital data (around 90% reduction in some methods) with compression technologies allows for more convenient storage and internet transmission of music with some, often significant, loss in quality.
Pirate Copies of Music
It was possible with the advent of tape recording to make copies of music from vinyl records and other tape recordings.
These unauthorised copies were initially tolerated when made by private citizens for their own convenience but when cheap copies began to be sold the music industry recognised a problem. This problem became far more severe with CDs which could be quickly copied in multiples and with good quality. The problem grew even greater when copies of music files from CDs could be shared through the internet. This lead to attempts to prevent copying by DRM (Digital Rights Management) which made copying on a computer more difficult. It also resulted in many experiments in making music available in different ways, leading to online libraries like Apple iTunes and eventually the currently popular streaming music.
Pre-Recorded Music
Music that is pre-recorded was for a long time not able to be very portable. Eventually cassette players and CD players became available but the media still was bulky and had to be carried along with the player. Using digital files allowed music that could be stored on a digital device for later listening without any media. While the compressed version of music is often used on portable devices and has consequent loss of quality, much of the loss may not be apparent due to the means of listening. With a mobile device, like a phone or tablet, it may require high end headphones to produce sufficient sound quality at the human ear to be able to detect the quality problems of compressed music. Many listeners will tolerate (or are not aware of) the quality problem for the convenience of always available music.
It is possible to copy files from a CD ('rip') and save these in a compressed format to listen to on a digital device, such as a phone or tablet. The recording is legal provided you own the CD and you only make one copy to other form for personal use. When ripping it is possible to select the level of compression to improve music quality but unless it is stored as a 'lossless' file, it will still be a poorer quality than a CD.
Streaming Music
Streaming music provides free or paid services where music of the user's choice is sent continuously to the selected device.
Virtually every streaming service uses some sort of compression so music quality is reduced, but again, unless good quality headphones or speakers are used, the compromised quality may not be evident to the listener. Some premium paid services will provide a higher quality stream rate but still well below the quality of a CD. The streaming service will still use significant data so care should be taken to understand how much it will cost.
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Creating Music
There are a number of apps that support music writing or playing.
These can be as simple as a 'tuner' app to assist with tuning, for example, a guitar.
Electronic instruments such as keyboards, and synthesisers are available but often may be included with music sequencers to have complete music composition apps.
While portable devices such as phones and tablets have sound recorder apps, serious musicians would not use such a device to record sessions.
High quality digital recorders are available for this purpose and can create standard computer files at CD quality or better.
They can be paired with high quality microphones to ensure a good quality of recording.
(Of course the best recording will be done in a recording studio!)