Spill (audio)
Encyclopedia
Spill is the occurrence in sound recording (particularly in close miking) and live sound mixing
whereby sound is picked up by a microphone from a source other than that which is intended. Spill is usually seen as a problem, and various steps are taken to avoid it or reduce it. In some styles of music, such as orchestral music, jazz, and blues, it is more likely to be accepted or even seen as desirable.
recording, as the combined signals during the mix process
can cause phase cancellation and may cause difficulty in processing individual tracks. It also causes difficulty in overdubbing, where the spill from the sound being replaced may still be audible on other channels. For sound reinforcement in live shows, mic bleed can make it hard for the sound engineer to control the levels of the different instruments and vocals onstage. For example, if an electric guitarist's loud amplifier is bleeding into the drum and vocal mics, it may be hard for the sound engineer to reduce the volume of the guitar in the onstage mix.
Spill can also introduce sounds which are not desired as part of the recording or live sound mix, such as the sound of a squeaking piano pedal, the clacking of keys on a bassoon, or the rustling of papers on a public speaker's podium.
Spill is sometimes accepted or even desirable, particularly in classical music
recordings, as it can create a natural sound between instruments. A guide to orchestral recordings notes that an ″...advantage in using a ribbon mic on the brass is that...there will be a slight pickup of the strings on
those mics which gives you a nice depth of field on the strings due to mic bleed (i.e., strings
bleeding into the brass mics on the other side of the stage)″. For some Classical recordings, the spacious sound of mic bleed is simulated. The ″SPACE programming module... uses delay and phasing to emulate positioning and microphone bleed within a heavily multi-miked sound stage that has come to define that [orchestral] film score
sound we are all used to hearing″.
This is also true for drum recording and productions that need a "live" feel. Whereas pop songs are often recorded one track at a time, for jazz and blues and other improvisation-based music, it is often desirable to have the band perform together, because this creates a better "feel" and more "swing", and because the musicians typically "feed" off each others' ideas in real time. For example, in a jazz tune, the "comping" musicians will alter their improvised accompaniment in response to the solo lines played by the saxophone player; as well, in some cases, the comping musicians will introduce melodic or rhythmic ideas which are picked up by the solo improviser.
In Jamaican reggae and dub, mic bleed is purposely used in recordings.
Spill is often experienced with vocal recording, when the accompaniment
is monitored
through speakers or open-backed headphones
. It may also be a problem in studios without talkback
facilities.
Spill is also avoided by using a 3:1 distance rule of thumb
, which states that for each unit of distance between a sound source and its microphone, other microphones should be placed at least three times as far.
For drums, to reduce bleed of the snare into the bass drum, several techniques are used. By using a small "...speaker wired as a microphone" to mic the bass drum, "bleed from the rest of the kit is never a problem".
Other methods of minimising spill include the use of noise gate
s.
' song "Yesterday
", where Paul McCartney
overdubbed his lead vocal. He had originally recorded acoustic guitar
and vocals together on different tracks, though the spill of vocals onto the acoustic guitar track gave an effect similar to double tracking.
Spill can also be heard on the vocal track of Christina Aguilera
's "Beautiful
". Engineer Dave Pensado said that although the vocal track contained spill from Aguilera's headphones, the "bleed is honest", which suited the song as it was "about being beautiful and honest in every way".
Live sound mixing
Live sound mixing is the art of combining and processing a number of audio signals together to create a "mix" that the audience or performers at a live show hear. There can be a variety of different mixes required, depending on the performance requirements...
whereby sound is picked up by a microphone from a source other than that which is intended. Spill is usually seen as a problem, and various steps are taken to avoid it or reduce it. In some styles of music, such as orchestral music, jazz, and blues, it is more likely to be accepted or even seen as desirable.
Occurrence
Spill occurs when sound is detected by a microphone not intended to pick it up (for example, the vocals being detected by the microphone for the guitar). Spill is often undesirable in popular musicPopular music
Popular music belongs to any of a number of musical genres "having wide appeal" and is typically distributed to large audiences through the music industry. It stands in contrast to both art music and traditional music, which are typically disseminated academically or orally to smaller, local...
recording, as the combined signals during the mix process
Audio mixing (recorded music)
In audio recording, audio mixing is the process by which multiple recorded sounds are combined into one or more channels, most commonly two-channel stereo. In the process, the source signals' level, frequency content, dynamics, and panoramic position are manipulated and effects such as reverb may...
can cause phase cancellation and may cause difficulty in processing individual tracks. It also causes difficulty in overdubbing, where the spill from the sound being replaced may still be audible on other channels. For sound reinforcement in live shows, mic bleed can make it hard for the sound engineer to control the levels of the different instruments and vocals onstage. For example, if an electric guitarist's loud amplifier is bleeding into the drum and vocal mics, it may be hard for the sound engineer to reduce the volume of the guitar in the onstage mix.
Spill can also introduce sounds which are not desired as part of the recording or live sound mix, such as the sound of a squeaking piano pedal, the clacking of keys on a bassoon, or the rustling of papers on a public speaker's podium.
Spill is sometimes accepted or even desirable, particularly in classical music
Classical music
Classical music is the art music produced in, or rooted in, the traditions of Western liturgical and secular music, encompassing a broad period from roughly the 11th century to present times...
recordings, as it can create a natural sound between instruments. A guide to orchestral recordings notes that an ″...advantage in using a ribbon mic on the brass is that...there will be a slight pickup of the strings on
those mics which gives you a nice depth of field on the strings due to mic bleed (i.e., strings
bleeding into the brass mics on the other side of the stage)″. For some Classical recordings, the spacious sound of mic bleed is simulated. The ″SPACE programming module... uses delay and phasing to emulate positioning and microphone bleed within a heavily multi-miked sound stage that has come to define that [orchestral] film score
Film score
A film score is original music written specifically to accompany a film, forming part of the film's soundtrack, which also usually includes dialogue and sound effects...
sound we are all used to hearing″.
This is also true for drum recording and productions that need a "live" feel. Whereas pop songs are often recorded one track at a time, for jazz and blues and other improvisation-based music, it is often desirable to have the band perform together, because this creates a better "feel" and more "swing", and because the musicians typically "feed" off each others' ideas in real time. For example, in a jazz tune, the "comping" musicians will alter their improvised accompaniment in response to the solo lines played by the saxophone player; as well, in some cases, the comping musicians will introduce melodic or rhythmic ideas which are picked up by the solo improviser.
In Jamaican reggae and dub, mic bleed is purposely used in recordings.
Spill is often experienced with vocal recording, when the accompaniment
Accompaniment
In music, accompaniment is the art of playing along with an instrumental or vocal soloist or ensemble, often known as the lead, in a supporting manner...
is monitored
Studio monitor
Studio monitors, also called reference monitors, are loudspeakers specifically designed for audio production applications such as recording studios, filmmaking, television studios and radio studios where accurate audio reproduction is crucial....
through speakers or open-backed headphones
Headphones
Headphones are a pair of small loudspeakers, or less commonly a single speaker, held close to a user's ears and connected to a signal source such as an audio amplifier, radio, CD player or portable Media Player. They are also known as stereophones, headsets or, colloquially, cans. The in-ear...
. It may also be a problem in studios without talkback
Talkback (recording)
In sound recording, talkback refers to the intercom system used in recording studios and production control rooms in television studios to enable personnel to communicate with people in the recording area or booth...
facilities.
Avoiding spill
Recording engineers and live sound engineers aim to avoid spill by:- Placing microphones closer to the sound source
- Using acoustic barriers (known as gobosGobo (recording)Gobo is a slang term used by sound recording engineers to refer to a movable acoustic isolation panel.An acoustics gobo is parallel in use to a photography gobo, which is used to block direct light sources, and also shares its name with the stage lighting gobo...
); for live sound, plexiglass screens are sometimes used for drums and brass. - Reducing sound reflection in the recording room (e.g., by draping blankets on walls and windows)
- Having the different instruments and amplifiers set up in different isolation booths or rooms (particularly with loud electric guitar amplifiers)
- Recording every instrument and vocal one at a time using a multi-track recording system.
- Using directional microphones
- Maximising the distance between sound sources
- Using DI unitDI unitA DI unit, DI box, Direct Box, or simply DI , is a device typically used in recording studios to connect a high-impedance, line level, unbalanced output signal to a low-impedance microphone level balanced input, usually via XLR connector...
s rather than microphones - Using piezoelectric pickups (e.g., with an upright bass)
- For vocalists, using closed shell headphones
- Cutting frequencies with an equalizer that are not present in the intended microphones's instrument or vocals (e.g., for a bass drum mic, all of the high frequencies could safely be cut; for a piccolo, all of the bass frequencies could be cut)
Spill is also avoided by using a 3:1 distance rule of thumb
Rule of thumb
A rule of thumb is a principle with broad application that is not intended to be strictly accurate or reliable for every situation. It is an easily learned and easily applied procedure for approximately calculating or recalling some value, or for making some determination...
, which states that for each unit of distance between a sound source and its microphone, other microphones should be placed at least three times as far.
For drums, to reduce bleed of the snare into the bass drum, several techniques are used. By using a small "...speaker wired as a microphone" to mic the bass drum, "bleed from the rest of the kit is never a problem".
Other methods of minimising spill include the use of noise gate
Noise gate
A Noise Gate or gate is an electronic device or software that is used to control the volume of an audio signal. In its most simple form, a noise gate allows a signal to pass through only when it is above a set threshold: the gate is 'open'. If the signal falls below the threshold no signal is...
s.
Examples
Spill is evident on The BeatlesThe Beatles
The Beatles were an English rock band, active throughout the 1960s and one of the most commercially successful and critically acclaimed acts in the history of popular music. Formed in Liverpool, by 1962 the group consisted of John Lennon , Paul McCartney , George Harrison and Ringo Starr...
' song "Yesterday
Yesterday (song)
"Yesterday" is a song originally recorded by The Beatles for their 1965 album Help!. The song first hit the United Kingdom top 10 three months after the release of Help!. The song remains popular today with more than 1,600 cover versions, one of the most covered songs in the history of recorded...
", where Paul McCartney
Paul McCartney
Sir James Paul McCartney, MBE, Hon RAM, FRCM is an English musician, singer-songwriter and composer. Formerly of The Beatles and Wings , McCartney is listed in Guinness World Records as the "most successful musician and composer in popular music history", with 60 gold discs and sales of 100...
overdubbed his lead vocal. He had originally recorded acoustic guitar
Acoustic guitar
An acoustic guitar is a guitar that uses only an acoustic sound board. The air in this cavity resonates with the vibrational modes of the string and at low frequencies, which depend on the size of the box, the chamber acts like a Helmholtz resonator, increasing or decreasing the volume of the sound...
and vocals together on different tracks, though the spill of vocals onto the acoustic guitar track gave an effect similar to double tracking.
Spill can also be heard on the vocal track of Christina Aguilera
Christina Aguilera
Christina María Aguilera is an American recording artist and actress. Aguilera first appeared on national television in 1990 as a contestant on the Star Search program, and went on to star in Disney Channel's television series The Mickey Mouse Club from 1993–1994...
's "Beautiful
Beautiful (Christina Aguilera song)
"Beautiful" is a song written by Linda Perry and recorded by American singer Christina Aguilera for Aguilera's fourth studio album, Stripped...
". Engineer Dave Pensado said that although the vocal track contained spill from Aguilera's headphones, the "bleed is honest", which suited the song as it was "about being beautiful and honest in every way".