In the past, almost all commercial music was mixed by an experienced professional recording engineer under the supervision of a producer and/or artist. Although this is still true at many levels of high-end production, with the emergence of the project studio, the vast majority of facilities have become much more personal and cost-effective in nature. The recording phase involves the physical process of capturing live or sequenced instruments onto a recorded medium. In order to understand the process of mixing, it's important to understand one of the most important concepts in all of audio technology: the signal chain. Many mixer and certain audio interface designs provide a break in the signal chain that occurs after the channel input. A direct send/return or insert point can be used to send the strip's line-level audio signal out to an external gain or effects processing device. Amplifiers, magnetic tape and even digital media are limited in the range of signal levels.