Resources

Intro to Field Recording

The following information was presented and discussed at our Intro to Field Recording workshop on April 6, 2019. It is presented here as a rough overview on sound and field recording basics.

Introduction to field recording workshop presented by Phonography Austin

BASIC ACOUSTIC CONCEPTS

BASIC RECORDING CONCEPTS

MICROPHONES

RECORDERS

MONITORING

COMMON FIELD RECORDING PROBLEMS

BASIC ACOUSTIC CONCEPTS

SOUND

Sound is both the changes in energy traveling through air molecules, and how we perceive those changes.

The room you are in looks empty, but is full of air molecules. Compressing the air molecules (by clapping your hands, for example) causes them to contract, then expand, compressing the air molecules next to them in a chain. Our ears and brain perceive that chain of air contraction and expansion as sound.

The speed at which the air molecules are compressed is expressed as frequency. This is not the speed at which that compression travels through the air, just how quickly it happens.

The intensity of that compression is expressed as loudness.

FREQUENCY

Frequency is how high or low a sound is. It corresponds to pitch, and is measured in Hertz (Hz).

  • In the national anthem (US), “land of the freeeeeee” progresses from a low to a high frequency.
  • On a piano, low notes are to the left and high notes to the right.

Not all sounds have an easily definable frequency – radio static is a random mix of frequencies, described as noisy or broadband sound.

LOUDNESS

Loudness is how loud or quiet a sound is.

When we talk about increasing loudness we often will say boosting; decreasing loudness is cutting.

Loudness is measured in decibels (dB), which is slightly different between analog electronics (dBV), digital electronics (dBFS) and acoustic measurement (dB SPL).

The word volume describes playback volume over speakers or headphones, not the actual loudness of a sound.

TIMBRE

Timbre is how bright or dark a sound is. It rhymes with amber.

Timbre consists of additional tones (harmonics) that are a higher frequency than the primary tone (fundamental). Harmonics often correspond mathematically to the fundamental but don’t always. Harmonics are almost always quieter than the fundamental.

  • A kazoo has a bright or rich TIMBRE.
  • Cutting bass and boosting treble creates a bright TIMBRE.
  • A foghorn has a dark TIMBRE.
  • Cutting treble and boosting bass creates a dark TIMBRE.

Unlike frequency and loudness, timbre is not easy to quantify.

ENVELOPE

Envelope describes how the components of a sound change over time.

The three components of an envelope are attack, sustain and release.

1. ATTACK

Attack describes the beginning of a sound.

  • A gunshot has a fast attack.
  • A gentle violin has a slow attack. Synonyms: swell, fade in, build-up.

2. SUSTAIN

Sustain describes what happens right after the attack.

  • In the national anthem (US), the words “land of the” have a sustain that is shorter than the word “freeeeeee.”
  • A motorcycle shifting gears has a timbre that changes from bright to dark while the sound is sustained.

3. RELEASE

Release describes what happens when the sustain ends.

  • A loud radio that is suddenly unplugged has a fast RELEASE.
  • An electric fan that is unplugged has a slow RELEASE.

 

BASIC RECORDING CONCEPTS

TRANSDUCTION

A transducer converts one type of energy into another.

Sounds start as

Mechanical energy – for example, applause, causing changes in

Acoustic energy – air molecules are compressed, causing changes in

Mechanical energy – the ear drum is compressed, causing changes in

Hydraulic energy – the fluid in the cochlea is compressed, causing changes in

Electrical energy – response in the auditory nerve system

ANALOG RECORDERS

Analog recorders take changes in acoustic energy, transduce them into electrical energy, then store them as magnetic energy.

They are typically not as accurate as digital recorders but can sound interesting.

They are typically more forgiving of sounds that are much louder than the input level you’ve set. Those sounds cause analog distortion, which represents the sound source more accurately than digital clipping. That doesn’t analog distortion accurate – just more so than digital.

DIGITAL RECORDERS

Digital recorders take changes in acoustic energy, transduce them into electrical energy, then convert and store them as digital data.

Bit depth refers to the range of loudness captured, typically 16 or 24.

  • Higher bit depth yields more realistic audio.

Sample rate refers to the frequency range captured, typically between 44.1 KHz and 96 KHz.

  • Higher sample rate yields more realistic audio, but a higher bit depth is a greater improvement if file size is a consideration.

Be aware that not all devices will play recordings made at higher bit depth and sample rates.

  • 44.1 KHz, 16 bit is most likely to play on any device.

If you see bit rate options (not bit depth),  you are recording in a compressed format, which you should avoid.

  • You will be losing data if you do.
  • If you must record in a compressed format, use the highest bit rate available.

Digital recorders are typically less forgiving of sounds that are over the maximum input level. They cause digital distortion or clipping, which is a very inaccurate representation of the sound source.

MICROPHONES

HOW MICROPHONES WORK

Microphones take acoustic energy and transduce them into electrical energy.

TYPES OF MICROPHONES

Dynamic

A paper diaphragm, suspended in a magnetic field, is moved by acoustic energy, which is then transduced into electrical energy via induction.

  • Dynamic microphones are very durable. Most are not very accurate.

Condenser

A very small metal plate is moved by acoustic energy, which is then transduced into electrical energy via capacitance changes between the plate and a backing plate.

  • Condenser microphones are very accurate, and not as durable as dynamic microphones.
  • Small diaphragm condensers are generally more accurate than large diaphragm condensers.

 

MICROPHONE POLAR PATTERNS

microphone polar pattern diagram

Polar patterns describe how a microphone responds to sounds coming from different directions.

Cardioid picks up sound mostly in front of the mic.

Omni picks up sound all around the mic.

Figure 8 or bidirectional picks up sound on either side of the mic.

Hypercardioid aka shotgun picks up sound mostly in front of the mic.

Multiple polar pattern mics can switch between patterns.

Stereo mics output two separate signals – right and left.

MICROPHONE FREQUENCY RESPONSE

microphone frequency response

Frequency response shows how well a microphone responds to different frequencies at the same loudness.

A flat frequency response is most accurate.

TYPES OF MICROPHONE CONNECTIONS

There are many connection types – standard XLR, minijack, USB, proprietary.

  • XLR is most common.
  • Not all are compatible.

 

MICROPHONE PROXIMITY EFFECT

A microphone within 6” of a sound source usually has an exaggerated response to bass from that sound source.

TYPICAL MICROPHONE SWITCHES

typical switches found on microphones

 

RECORDERS

ANALOG

Analog cassette/microcassette

  • Typically have bad built-in mics, and sound bad.
  • Media is currently hard to find.
  • Difficult to maintain.
  • Convenient.
  • Discreet.
  • Inexpensive (less than $50).

Analog portable reel-to-reel

  • For professional production.
  • Usually let you use standard (XLR) mics.
  • Can sound amazing.
  • Media is currently hard to find, and expensive.
  • Difficult to maintain.
  • Not convenient or discreet.
  • Expensive ($300-up).

 

DIGITAL

Digital voice recorders

  • Not high quality.
  • Rugged.
  • Convenient.
  • Discreet.
  • Inexpensive ($20-$100).

Digital handheld field recorders

  • Typically have built-in mics. Some have proprietary mics.
  • Some have standard (XLR) mic inputs.
  • Can be somewhat high to high quality.
  • Rugged.
  • Convenient.
  • Discreet.
  • Mid-cost ($75-$400).

Digital production recorders

  • For professional production.
  • Usually let you use standard (XLR) mics.
  • High to very high quality.
  • Rugged.
  • Not convenient.
  • Not discreet.
  • Expensive ($1K-up).

Smartphones

  • Can use external or built-in mics.
  • Many recording apps available.
  • Can be somewhat high to high quality.
  • Very discreet.
  • Use “Airplane” mode to reduce interference.

Laptops

  • Can use external built-in mics.
  • With an audio interface can use external mics.
  • Not preferred for field work as they are fragile.

RECORDER OPTIONS

File format options (for digital recorders)

  • MP3 is compressed data; not a perfect representation of the recording.
  • WAV files are more accurate but take up more space.

Levels

  • Get hot levels: record as loud as you can.
  • Don’t clip: don’t let your levels go in the red.

Limiter/compressor

  • Useful to prevent clipping/distortion.
  • Overuse will make sound flat/crunchy.
  • Lower threshold is more limiting/compression; higher threshold is less.
  • Ratio is the amount of compression; 1:1 is none, 1:20 is very severe.

AGC (automatic gain control)

  • Typically for voice recorders or apps, boosts quiet bits and cuts loud bits.
  • Best to disable if you want an accurate recording.

High-pass/low-cut filter

  • Cuts low frequencies.

 

MONITORING

Headphones

  • Don’t spend more than $100.
  • Over-ear are more accurate than earbuds.
  • Earbuds are also not good for your ears.
  • Wireless headphones are inaccurate.
  • Ignore all the above if you have headphones that you like and get good results with.

Speakers

Typically not used in the field.

  • Speakers are heavy.
  • Speakers would cause feedback if used with a live microphone.

Going without monitoring

Experiment with not monitoring your recordings over headphones.

  • Easier to be more discreet.
  • You won’t detect any problems that might come up.

 

COMMON FIELD RECORDING PROBLEMS

Loud and low frequencies from wind

  • Use a DIY or commercial wind screen.
  • Position mic away from wind.
  • Use a high-pass filter.
      • Not effective if the diaphragm is clipping.

Excessive low frequencies

  • Use a high-pass filter.
  • Experiment with microphone positioning.
  • Try a different microphone.

Mechanical or handling noise vibrating mic

  • Use a DIY or commercial shock mount.
  • Practice holding the microphone in a quiet room.
  • Use a tripod/gorilla stand.

Too much ambient sound

  • Use a boom pole or selfie stick.
  • Get closer to the source.
  • Use a more directional mic.

Electronic interference

  • Turn your mobile phone or any other devices off.
  • Move away from any electronic devices.
  • Try other cables.
  • Try other headphones.