Intro to Audio Tech - Lecture 5 (Analog Recording)

Analog Defintion

Comes from the word analogy, meaning things that are like eachother in some significant way.

What does analog recording store?

Stores a waveform that is analogous (same) to the way the air pressure changed.

What does magnetic analog recording store?

Stores a changing magnetic field.

What is analog tape?

A long strip of plastic that is coated with tiny magnetic particles.

How are these magnetics on the tape aligned initially?

Randomly.

What does the recorder do to the tape?

Realigns the magnetics on the tape into a positive and negative pattern that is analogous to the positive and negative waveform of the changes in air pressure.

What is a recording head?

An electromagnet.

What is a electromagnet?

A piece of metal with a conductor wrapped around it that sends a varying voltage to the wire and it creates a varying magnetic field.

What does all professional recorders have?

Three heads.

What are the three heads on the recorder?

The erase head, record head, and playback/repro head.

How does a playback/repro head work?

Like a record head but in reverse. When a varying magnetic field passes across the repro head, a varying voltage is produced. That voltage can be amplified and played back on a speaker.

What is problem number one with analog recording?

The transfer of magnetic energy from the recording head to the tape is not linear.

What do weak magnetic fields not do?

Magnetize the tape or “stick”.

What is zero cross distortion?

Every time a signal crosses from positive to negative or vice versa, there is a weak magnetic field. This means that every time that a signal crosses the zero point there will be distortion.

What do all signals near zero become?

Zero.

What is the solution to zero cross distortion?

Sending a very high frequency (around 150kz) to everything recorded called bias. All analog recorders have bias built in and the recorders remove the bias tone on playback.

What is gap loss?

The playback or repro head must see a difference in a magnetic field between each side of the head gap. At a high enough frequency, the wavelength becomes too short and there will be no difference between one side of the gap and the other. This is the practical high frequency limit of the recorder.

How to help gap loss?

Making the head gap small and moving the tape faster both raise the frequency at which gap loss occurs.

What is tape saturation?

The limit to how strong a signal can be recorded. Strong magnetic fields utilize more magnets to represent them on tape.

Why is tape saturation sometimes desierable?

The distortion it creates is quite pleasing as a creative choice. Creates a warmer and deeper sound.

What is tape hiss?

Randomly aligned magnets produce random frequencies or white noise. This is caused by low or weak signals as they dont use all of the magnets that are on the tape. Low recording levels will have more tape hiss while higher levels are less noisy.

What is crosstalk?

Magnetic bleed on adjacent tracks on a tape. A natural consequence of storing magnetic fields near each other.

What is print through?

Magnetic bleed on adjacent windings of tape. A natural consequence of storing magnetic fields near each other.

What are track formats?

The layout of magnetic channels on the width of a reel of tape.

What are common track formats?

1/8’’, 1/4’’, and 1’’. 2’’ format is typically used for 24 tracks.