Analog Tape Recording

The Music Telegraph | Text 2019/04/13 [10:36]

Analog Tape Recording

The Music Telegraph| 입력 : 2019/04/13 [10:36]

▲ Analog Tape Deck mechanism

The tape is a strip of plastic which has been coated with a material that is easily magnetized. (The most commonly used material is highly refined rust, or iron oxide.) The capstan is a spinning post. The tape is held tightly against the capstan by the pinch roller and dragged across the three heads at a steady rate.

All three heads are essentially the same in construction: a C-shaped piece of metal with the very narrow gap of the "C" near the tape. A coil of wire around the metal can serve to either detect or produce magnetic fields at the gap. If a strong current is passed through the coil, a field is produced which creates a magnetic spot on the nearby tape. The amount of magnetism will be proportional to the amount of current. If the tape is moved and the current varied in a periodic way, a "track" of magnetic areas will be imprinted on the tape. All of this happens at the record head. When the tape subsequently passes the play head, the varying magnetic field on the tape produces a varying current in the play head coil, which can be detected by some sensitive electronic circuitry. (The erase head works just like the record head, but at a super high frequency which will not be recorded but which will obliterate any existing information.)

© University of California, Santa Cruz 

 

 

 

Analog Tape Recording

 

 

Domains of Analog Tape

The smallest particle that can be considered a magnet when new are all aligned 

- They will be randomized at the erase head. This erases any previously recorded signal & causes tape 'hiss'

▲ Analog tape domains

© The Music Telegraph



 

Bias

- A high frequency, Hi level sine wave between 100 kHz & 400 kHz

- Applied at the erase head (to randomize domains) & at the record head - to get domains in motion so that they will stay in the pattern of the applied audio system

- Bias increases frequency response & decrease dropout sensitivity, noise & distortion

 

 

 

Analog Alignment

(1) Play mRL (magnetic Reference (ab)) test tape

- 1k tone to set repro(-duction) level,

- then 10k tone for HF adjust

- then 100 Hz tone for LF adjust

 

(2) Record head

Use stock (session) tape set oscillator to 10kHz @ +4 dBm output

- Record this tone, monitor repro head

- Adjust bias pot to lab manual specifications

; then record 1k, monitor repro., adjust record level to 0vu

; then record 10k, monitor repro., adjust record HF level to 0vu

; then record 100 Hz, monitor repro., adjust record LF to 0vu

 

 

Shuttling: alternately activating FF & REW to slow/fast wind before hitting stop

 

 

Rocking the Reels: both hands on reels, move tape back & forth to find edit points

 

 

Punch In / Punch Out

- used when over dubbing onto a track with signal already recorded on it 

- safetest way to punch out of record: hit [Safe & Rew] at same time 

▲ Punch In/Out recording

© The Music Telegraph



 

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