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.