Trying to get a clean and high quality recording, but can’t seem to get it? Or maybe you just think that your microphone is not performing at its best? There are many factors that will affect the outcome of your recordings, whether at home or on stage. One such factor that we are covering today is the “Audio Spill”. Which naturally begs the question – What is an “Audio Spill”?
In today’s article, we will go through the various aspects of this vital concept. Hopefully by the end of this post, you will understand how this phenomenon affects the quality of audio recordings, in both the positive and negative way. We will also cover some methods that professionals use in order to reduce its detrimental effects. So do not waste any more time, and read on!
Commonly referred to as bleed or leakage, audio spill is a term used to describe an occurrence, where a microphone picks up sound coming form another source (one that it is not intended to record). This often happens in both studio and live recording situations (where multiple sound sources are miked up at once).
Although the general consensus (among audio professionals) is that audio spill is often a problem rather than a benefit, it does still have its exceptions. In the case of some genres of music, such as orchestral music, jazz, and blues, it can often be seen as acceptable or at times, even desirable. Regardless, audio engineers are constantly coming up with methods in order to reduce the effect of audio spill.
Let us now look at the two topics we will cover on this subject:
- Undesirable effect
- Desirable effect
- Avoiding audio spill
- Examples in music
Audio spill takes effect when sound is captured by a microphone that is not meant to record it (for instance, vocal performance being captured by the microphone for a guitar amplifier). Generally, audio spill is undesirable even in popular music productions, as the combined signals may cause “phase cancellation” and makes processing individual tracks during the mixing stage, problematic.
Mixing techniques such as “overdubbing” will also be difficult, as the audio spill from the sound that needs to be replaced (part of the overdubbing process) may still be present on other channels, and might also be audible. For live sound reinforcement systems in live shows, mic bleeds (audio spill) prevents the sound engineer from having the best level control for each sound source on stage.
Take for example, if sound from an electric guitar’s loud amplifier bleeds into the snare and kick mics, the sound engineer will have difficulty controlling the volume of the guitar in the overall mix. Other undesirable sounds (in a live performance) can also be introduced by spills, 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.
There are exceptions where audio spill is desirable, typically in classical music productions, where it creates resonance between instruments. An orchestral recording guide notes this – ″…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)″.
Audio spill has also been found to be a benefit for multi-track drum recording and productions that need a “live” feel. For musical genres such as jazz and blues, or other improvisation-based music, having the band perform together (which results in audio spill) is often seen as desirable. This is because it creates a better “feel”, and musicians typically “connect” with each other much better in real time.
A perfect example of this would be an improvisational jazz tune, where the “comping” musicians will alter their improvised accompaniment accordingly, responding in real-time to the lead or solo lines played by the saxophone player. This can also work the other way, where the comping musicians will introduce a change in the melodic or rhythmic structure, which are then picked up by the solo improviser.
Avoiding Audio Spill
In many cases, it is almost impossible to completely negate or nullify the effects of an audio spill. However, sound engineers and audio professionals everywhere have been using many methods, in the aim of minimizing the damaging effects of an audio spill. In this section, we will cover in a little more detail about some of the more well-known or well-used methods.
The close miking method involves placing microphones closer to the sound source that needs to be recorded. This is a very simple technique that many sound engineers and technicians use all over the world, in almost every recording situation that you can think of, whether in the studio or at a live venue. The major benefit of using this method is that it rarely requires any other extra equipment, other than the microphone and the mic stand (or clamp).
Also known as “Gobos”, acoustic barriers are very often used to enhance the isolation of sound sources. There are many types of acoustic barriers that are used for a variety of audio recording applications. Perhaps the most obvious example of an acoustic barrier in a live sound application, would be the plexiglass screen. These screens are often used to isolate a drum kit in a band, and offers better soundproofing.
This method is often used in home studios and professional recording studios. There are various types of isolation booths, each used for different instruments and recording purposes. These booths help to enhance the recording quality by providing a better acoustical response for any musical performance. Typical uses of isolation booths include the recording of vocals, electric guitar amplifiers and also bass amplifiers.
Here is a list of other known methods also used to reduce audio spill:
- Recording each instrument or sound source one at a time, using a multi-track recording system
- Using directional microphones (for better sound isolation)
- Maximising the distance between sound sources (to prevent leakage)
- Using DI units for a direct and clean signal transmission
- Installing soundproof materials in recording rooms
- Making use of piezoelectric pickups for acoustic instruments (e.g., upright bass)
- For vocalists, using closed back headphones during recording
There is also a rule that sound engineers can follow, which is known as the “3:1 distance rule of thumb“. This rule 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.
Examples in Music
Let us look at some examples of how audio spills have contributed to the creative direction of popular music. The first one is the song “Yesterday” by The Beatles’, where Paul McCartney overdubbed his lead vocal. He initially had recorded acoustic guitar and vocals together on separate tracks. However, there was a “vocal spill” onto the acoustic guitar track, which produced a “double tracked” effect.
Another popular example would be Christina Aguilera’s song called “Beautiful”, where an audio spill had occurred on the vocal track. The engineer for the song’s production, Dave Pensado, stated that although the vocal track was affected by the spill from Aguilera’s headphones, the “bleed is honest” and it suited the song, which was “about being beautiful and honest in every way”.
Okay, we have reached the end of this article. Hopefully, you people now have a decent understanding of this phenomenon of audio spills, and will be able to achieve even greater sounding mixes in the future!
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