The production on "Strawberry Fields Forever" was especially complex, involving the innovative splicing of two takes that were recorded in different tempos and pitches. Emerick remembers that during the recording of "Revolver", "we had got used to being asked to do the impossible, and we knew that the word 'no' didn't exist in the Beatles' vocabulary." A key feature of "Sgt. Pepper" is Martin and Emerick's liberal use of signal processing to shape the sound of the recording, which included the application of dynamic range compression, reverberation and signal limiting. Relatively new modular effects units were used, such as running voices and instruments through a Leslie speaker. Several innovative production techniques feature prominently on the recordings, including direct injection, pitch control and ambiophonics. The bass part on "Sgt. Pepper's Lonely Hearts Club Band" was the first example of the Beatles recording via direct injection (DI), which Townsend devised as a method for plugging electric guitars directly into the recording console. In Kenneth Womack's opinion, the use of DI on the album's title track "afforded McCartney's bass with richer textures and tonal clarity".