Most record players have audio connections that can be hooked up to speakers or a sound system, but a universal serial bus (USB) turntable is designed specifically to plug into a personal computer. The purpose of connecting a turntable to a computer is typically to digitally encode the analog sound data contained on a record. In some cases a USB turntable can contain all the hardware necessary to record and encode the audio data, in which case it is possible to plug the device directly into a compatible portable music player.
Phonographs have been around since the middle of the 19th century, and they became a popular storage medium for music during a large part of the 20th century. Early models used wax cylinders and other methods to store analog sound data in grooves that varied in depth. Later phonographs used round, flat discs with tightly wound spiral grooves that a needle would travel down as the record turned. The varying depth of the groove was typically used to generate an electrical signal via a piezoelectric device or magnetic cartridge. Some modern record players can accomplish the same task by optically reading the depth of the groove with a laser.
Record players were largely replaced by other media, such as compact discs (CDs) and digital formats. In order to enjoy older music on modern digital devices, a USB turntable can be used to perform a conversion. These turntables operate in much the same fashion as old record players, but the audio signal is either converted and encoded within the device or transmitted as an electric signal to a PC.
The simplest type of USB turntable outputs an audio stream to a PC. Software on the computer can be used to capture the audio stream, typically in the form of an uncompressed file. Various techniques can then be used to clean up the recording, because record players sometimes generate undesirable hisses or pops during playback. These uncompressed files can then be converted into a variety of different compressed music formats that can be played on a PC or a portable music player.
Another type of USB turntable is capable of performing the entire encoding process itself. These turntables can sometimes be plugged directly into a portable music player. The songs on the album are recorded and encoded, and they can be automatically transferred to the music player or storage device without the use of a computer. Other more complex USB turntables can also use bidirectional controls so that the record player is actuated by the computer. Special programs allow this type of USB turntable to automatically drop the needle at the beginning of a desired song.