1.2 Proximity Effect

  • The proximity effect is when low frequencies are emphasised when you get closer to the microphone
  • This can be fixed by moving further back or by using EQ later on. Sometimes this effect is used to give a ‘warmer’ sound
  • It occurs in directional (cardioid, hypercardioid or figure of 8) microphones
  • The diagram below shows the proximity effect at different distances away from the microphone.

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1.1 Hardware: DI Boxes

DI Boxes

  •  DI boxes (direct input) are used to eliminate the need to mic up electronic instruments.
  • They can be plugged directly in to a mixer or audio interface.
  • They convert an unbalanced (two wire) signal to a balanced (three wire)
  • Microphones usually use XLR connections (Extra Low Resistance).
  • Balanced cables use phase cancellation to reduce noise; they copy and invert the sound signal at both ends then use the resulting signal to cancel out noise.

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1.1 Hardware: Audio Interfaces

The picture below shows a simple FocusRite audio interface with two separate inputs.

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  • Latency can be an issue when using external audio interfaces. This is when there is a delay between playing the signal and either the computer recording it or hearing it being monitored back.
  • This is very off putting when performing and can mean that the ‘feel’ or ‘groove’ of the song is lost and even the performance ending up out of time
  • Audio quantise functions can sometimes help to improve this, as can reducing the buffer size on your DAW
  • CD quality recordings use a sample rate of 44.1kHz and a bit depth of 16 bits.
  • Even some relatively inexpensive audio interfaces can record at higher bitrates, such as 48kHz and 24 bit.
  • The Red Book Standard outlines the requirements for digital audio and CDs
  • A higher sample rate improves the capture of higher frequencies and thus the higher frequency response. Nyquist’s theorem states that the highest frequency captured is half of the sample rate, and thus to capture the human hearing range, a sample rate of at least 40kHz must be used.
  • Benefits of using a higher bit depth include capture of wider dynamic ranges and minimising noise.
  • In order to capture or play back digital audio, some conversion needs to take place. Thus, audio interfaces incorporate analogue to digital converters (ADCs) and digital to analogue converters (DACs)
  • Audio interfaces will normally incorporate some kind of meter. This shows the volume of the input or output signal and allows the operator to avoid distortion.

 

XLR / Jack / Combi Inputs

·      There are two combi inputs. These can take both XLR connections and jack connections.

·      Jack connections can be TS (tip/sleeve) and TRS (tip/ring/sleeve).

·      XLR connections are balanced. This reduces noise using phase cancellation from combining two signals with opposite polarity and the resulting destructive interference

·      XLR connections are often used for microphones; jack connections for electric guitars and synthesisers

·      There is a locking tab at the top of the connection which means that the XLR cable does not come loose when pulled without pressing the locking tab

·      A pre-amp will amplify the input signal as part of the audio interface

Gain / Level / Pad

·      For each input, you can select between instrument and line level.

·      The gain control is used to set the input for a good signal to noise ratio and thus reduce noise and prevent distortion

·      The pad switch reduces the sensitivity in order to prevent distortion if the signal being recorded is loud. Pad switches often reduce the input signal by up to 20dB.

Phantom Power / LED Indicators

·      The 48V switch activates or deactivates phantom power.

·      This is used to supply power to a condenser microphone or active DI box

·      The interface only has one switch so this controls phantom power for all channels

·      This would create issues if using a condenser and a ribbon microphone as phantom power would break a ribbon microphone

·      MIDI stands for Musical Instrument Digital Interface

·      It is used as a language to communicate between different electronic instruments

·      The LED identifies when a MIDI signal is being sent or received

·      The second LED identifies when a USB connection to a computer is active

Headphones

·      Headphones can be used to monitor the signal

·      The headphone socket is a TRS/stereo jack connection. It can be used to provide a monitor mix (this may be different to what would be coming out of the monitor speakers).

·      On this interface, you can change which output the monitor output mirrors, and use the knob to change the volume of the headphones to ensure a good monitor level and avoid damaging your hearing

USB Connector

·      USB stands for Universal Serial Bus

·      It allows the interface to be connected to a computer and is used for transferring data

·      Power can be provided on a USB cable

·      USB 2.0 is a development of the original USB protocol, but is not as fast as ThunderBolt (Apple) and FireWire (IEEE 1394) connections.

MIDI Ports

·      These connectors are 5 pin DIN-180 connectors

·      They can be used to connect other equipment such as synthesisers and effects units

·      Equipment is connected together in a loop, with the MIDI out of one piece of equipment being connected to the MIDI in of the next piece

·      Some interfaces incorporate a MIDI-thru connector, which reduces the latency on the MIDI network

Outputs

·      All sets of outputs here are in stereo, and are analogue

·      There are two sets of unbalanced phono / RCA connections.

·      The red connector is for the right channel and the white for the left

·      Unbalanced connectors are are more susceptible to interference and have a poorer signal-to-noise ratio than balanced connectors

·      The two jack outputs are balanced; they are using a TRS jack connector

 

3.3 Tape Delay

Tape Delay

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  • The peak level will illuminate if the signal clips or distorts and the VU meter shows the input level in volume units.
  • The mic/instrument volume is the gain. This can be decreased to avoid clipping. It can be turned up to obtain a better signal to noise ratio.
  • The instrument volume is for a low impedance instrument such as guitar.
  • The mode selector is used to select different taps / patterns / rhythms / types of delay / number or volume of repeats / combinations of playback heads.
  • The bass and treble controls are used to modify the tone of the delay (not the dry signal). It is a shelving filter that adjusts the levels of low and high frequencies.
  • The reverb/echo volume is the wet/dry effect mix. “Straight” gives no echo at all. This is the gain, and has a spring reverb unit.
  • Repeat rate is the delay time / the amount of time between each repeat.
  • Intensity is the feedback amount/number of repeats. This is the gain.
  • The power switch should be used so that the unit should be switched off when not in use to preserve the life of the tape.
  • Echo normal or footswitch works as a bypass (to switch off the machine).
  • HML gives different output levels/volumes so that the unit can match the different signal levels required by different studio equipment.

3.3 Introducing Tapes

What a Tape Is Made Of

  • They contain two reels of magnetic tape. The tape is coated with iron oxide.
  • The sound quality of cassette tape is not as good as studio tape, with a reduced high frequency response because the tape moves slowly at 1 and 7/8 inches per second, and the tape is narrow.
  • The speed of the tape is controlled by the capstan or pinch roller.
  • Mono tapes have one track on each side (so two in total)
  • Stereo tapes have two tracks on each side (so four in total)
  • Multitrack tapes have four tracks but only play one way
  • Tape lengths are 60, 90 and 120 minutes, but 120 minute tapes often snapped
  • Tapes had erase protection tabs which meant that when broken, a tape could not be recorded on.
  • Tapes could be ‘dubbed’, which raised concerns about piracy, especially when a technology called ‘high speed dubbing’ was developed.

 

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Drawbacks of Tape

  • Cassette tapes are prone to hiss, so Dolby Noise Reduction was developed. This boosts the high frequencies when recording and reduces them on playback.
  • Tape saturation occurs when an increase in the strength of the sound source and thus electrical signal cannot produce an equivalent increase in magnetisation on the tape head. This leads to a form of subtle compression.
  • Cassette tapes can stretch
  • Iron oxide wears off tape over time which means that an oxide build up can occur on the tape head
  • Thus many companies marketed tape head cleaning cassettes which, combined with a chemical, removed oxide from the tape heads.
  • Cassette tapes are prone to print through, which is where the music is heard as an echo before it plays
  • Tape has a leader tape, which cannot be recorded on. This lasts for 2-3 seconds and draws the tape through onto the other reel.

3.3 Vinyl and Records

Vinyl Records

  • Before the invention of tapes, compact discs and MP3 players, people listened to recorded music on record players.
  • With no fast forward or rewind controls, you chose an album and enjoyed about 25 minutes of music by one artist before flipping it over for more or putting another record on the turntable.

 Producing a Vinyl Record

  • A master recording is made, usually in a studio where engineers perfect the recorded sound.
  • Then an object called a lacquer is placed on a record-cutting machine, and as it rotates, electric signals from the master recording travel to a cutting head, which holds a stylus, or needle.
  • The needle etches a groove in the lacquer that spirals to the centre of the circular disc. The imprinted lacquer is then sent for mass production.
  • A metal master is produce that is an inverse copy of the final record. This is made into a stamper.
  • The stamper is placed in a hydraulic press, and vinyl is sandwiched in between.
  • Steam from the press softens the plastic as the stampers push an impression of the master recording onto it.

 

What is a Record?

  • The sound is stored on a single spiral groove. This groove stores a form of the waveform. Each side of the groove has a separate signal for stereo.
  • The outer ¼ inch is the lead in so the stylus can lowered onto the recording without damaging the recording.
  • Some records featured a lock groove which stopped the tone arm from going onto the centre of the record. Some bands recorded continuous music in this.
  • Records were and in some cases still are released in 7/10/12 inch sizes, with a speed / RPM of 33 1/3 /45/78

 

The Physics of Records

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The Record Player

  • The turntable is the circular plate on which the record sits.
    • A rod positioned in the center holds the record (which has a hole in its center) in place.
    • The metal turntable is covered in rubber or plastic, which protects the record from being scratched. The turntable rotates or spins with the help of either a belt drive or direct drive system.
  • The stylus, or needle, is the smallest and perhaps the most important component of the record player.
    • It is made from a diamond or other hard material, shaped like a cone and suspended by a flexible strip of metal.
    • The pointed end is the only piece that touches the top of the record and it rides around the spiraling grooves of the disk, picking up the vibrations which are ultimately turned back into sound.
  • The stylus sits at one end of the tone arm, which is mounted to the side of the turntable and sits parallel to the record.
    • With the needle or stylus placed in the outermost groove of the record, the tone arm follows the groove as it spirals inward, traveling across the record in an arc as the record spins under it
    • As this happens, the vibrations travel along a flexible metal strip and wires housed in the tone arm to the cartridge in the end of the tone arm.
  • The cartridge receives the vibrations, converted to electrical signals through a coil in a magnetic field.
  • The electric signals are carried along wires to the amplifier which enhances the power of the signal.
  • Finally, the signals are converted back to sounds that come out through the speakers.
  • Initially, recorded sounds were in mono, meaning all of the sound signals are combined and come through one speaker or channel.
  • The introduction of stereo sound systems in 1958 allowed for a richer, more lifelike sound as two sets of sound waves were recorded.

 

Record Resurgence

  • Many music lovers just prefer the sound of a vinyl record.
  • They argue that, despite the occasional extraneous noises on a record from dust or a scratch, vinyl has a deeper, richer sound than a digital version, which can feel too perfect.
  • They also enjoy other aspects of records, such as liner notes, photos, posters and other album extras.

 

Drawbacks of Vinyl

  • Record players need a flat surface and are prone to feedback. Sound quality deteriorates towards the centre of the record. This is because records have a constant rotation speed which gives varying amounts of vinyl per second travelling under the stylus.
  • Low frequencies are reduced on the record to reduce wide stylus movement. Record player amplifiers apply an EQ on playback to return the low frequencies to their correct level.
  • Records are prone to scratching and dust. This causes crackle, hiss and jumps on playback.
  • Due to the material, vinyl often needs dusting with a special duster to avoid a static charge building up which attracts dust. The record sleeve is made of polythene and helps reduce the charge.
  • Records can warp when exposed to heat, which causes fluctuations in pitch like wow and flutter.
  • Due to the nature of a record player, they are prone to rumble at less than 30Hz.

1.12 Creative Effects

Vocal Effects

talkbox creates a vocal effect which is often applied to a guitar. The musician uses the mouth to change / shape the frequency content of sound. They use a tube to do this whilst changing the shape of their mouth; this is mirrored in the frequency change in the original audio.

 

A vocoder analyses the vocal signal and applies it to a synth timbre. It sounds ‘robotic’ and the voice follows the pitch from the synth.


Other Creative FX

A ring modulator creates a dissonant effect that creates metallic and ringing sounds. It creates frequency products by adding and subtracting the input frequencies.

Autotune

Overuse of pitch correction or autotune (a quick response time) forces the note to the nearest pitch set by the user / scale. It is often over-used in R&B music to create a slightly robotic effect, or subtly to keep vocalists in tune.

 

The term pan comes from ‘panorama’ in cinema. Auto-pan controls the place in the stereo field and is used to introduce creative panning throughout the stereo field. In tracks from the 60s and 70s, tracks were often extreme panned due to the limitations of technology.

A pitch shift alters frequencies and changes the musical note that is played. Harmonisers are intelligent pitch shifters that can add a musical interval to a part (e.g. a 3rd above).     These effects would have been created historically by slowing down or speeding up a tape.