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What is an “Audio Spill” – A concept you need to know!

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!

Introduction – The PrincipleMic Recording

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

Undesirable Effect

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.

Phase Cancellation

Sound “cancelling” each other / Photo by Haade / CC BY-SA 3.0

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.

Desirable Effect

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)″.

Orchestra Recording

Photo by Fionoula / CC BY-SA 3.0

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.

Close Miking

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).

Snare Miking

Photo by Unripe Content / CC BY 3.0

Acoustic Barrier

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.

Isolation Booths

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.

Guitar Isolation

Amp isolation booth / Photo by guitarDouchebaggery / CC BY 3.0

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

Paul McCartney

Paul McCartney / Photo by Fiona / CC BY-SA 2.0

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!

Do leave a comment or question below and share this article if you like. Thanks for reading!

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Farhan

When I'm not rocking out to great music, I'd prefer to be sleeping on a field on a windy day =)

10 Comments

  1. Thanks for an interesting and informative article on audio-spill that can happen when recording . It applies to several areas of my life…

    I listen to music, so now can listen to the sounds in a bit more of a discerning manner…Secondly, I do audio recordings for videos that I use in my online marketing program, and lastly, I am a muso of sorts…

    Regarding the last item I used to play in a band eons ago, as a young lad, and now hang around a lot of musos here in Dubai. So we do talk about audio-spill and best ways to get the desired sounds when playing gigs…

    This is a subject for my online program that I will look at closer – right now I am using a cheap mike (condenser) but it works for the moment.

    Do you have any recommendations for a decent mike for recording voiceovers, hosting webinars, and doing podcasts? I will be upgrading, and any info you could provide would be helpful.

    • Hi Dave!

      As for recommendations, it would help a lot if you would tell me the exact model or brand of your current microphone. This would allow me to give you a better recommendation.

      But in any case, do take a look at my product review page. I have reviewed a few microphones that I will definitely recommend for your projects.

      Since you are using a cheap condenser, I think you would love this for an upgrade: http://myaudioeducation.com/akg-c214-review-an-ide

      Thanks a lot for your comments and do visit my site again sometime =)

  2. Hi Farhan, You have answered a lot of questions I’ve never asked, I all way wondered how they could separate the instrument in a recording. I do have a question for you though. What are those ear plugs that you see entertainers where on stage. If they are so they can hear themselves how do they stay in tune and in time with everyone else?

  3. Well I have learned something completely new today. I know you geared this article towards music. How would this information apply in a film setting? (my son is a film student and sound is not his strong suit).

    My next question how would you set up audio if someone wanted to record a teaching video but didn’t want audio spill from say a squeaky chair or moving stuff around on a table?

    • Hello Nancy!

      Your question is pretty broad, and thus it is difficult for me to address. There are various ways in which audio is applied in filming, however all I can say at this point is that, audio spill often happens when you are filming a scene on location.

      For your second question, it is impossible to completely nullify the effects of an audio spill. Recording a live lesson in class, will often capture other sounds from the environment as well. In fact, it is usually seen as normal to have these sounds in the recording. Hence, my advice will be to use a separate “clip microphone” for the speaker, in order to have the best audio recording of the lesson.

      Thank you for dropping by!

  4. This is a very interesting page! My mom does recording and production of her own stuff, I’m going to show this to her. I really liked how you explained it in such a way that people with no past music experience can understand it. I also really liked how you added helpful pictures, which made what you were saying that much clearer! Great job! 🙂

    • Hello Trista!

      It is great to know that you have found this article very educational. I have always intended to write all my posts in a way that anyone can understand and appreciate. Thus, reading your comments really made my day!

      Do come back for more!

      Cheers!

  5. I used to make beats back in college, and started to get into the various audio engineering aspects. I didn’t get the opportunity to delve too deep down into some of the standard audio concepts when corporate America whisked me away, but I have always loved music and would love to get back into it. Conceptually, I thought my beats were very good, but lacked that professional engineering touch to take them to the next level.

    Audio spills were one of the concepts I came across but likely didn’t know how to term it. Do you have good recommendations on removing audio spills once they occur, or do you recommend just doing the take over?

    • Hi Ciandress!

      When it comes to dealing with audio spills, prevention is always better than cure. Recording clean is always ideal for any music production. In the case where an audio spill is identified after recording (during mixing process), then the best option would be to use a “noise gate” plugin (in your DAW) in order to cut out the unwanted noise (as much as is practically possible).

      Of course, if it is possible to re-record the particular track that is affected, then that would be ideal.

      Thanks for dropping by!

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