Media Preservation Labs Signal Notes, Controlled Vocabularies, and Syntax Guide

Table of contents

  1. Audio Terms
  2. Sample Audio Signal Note
  3. Explanation of Audio Terms

Audio Terms

  • Ambient noise
  • Audible edit
  • Bad pack
  • Begins abruptly, Ends abruptly
  • Blocking (layer-to-layer adhesion)
  • Break, Snap, or Rip
  • Broadband noise
  • Bubble
  • Bump
  • Buzz
  • Buckling
  • Center start disc
  • Change of mic position
  • Chatter
  • Chip
  • Clicks and Pops
  • Cinching
  • Coating transfer
  • Corrosion or Rust
  • Crackle
  • Cracks
  • Crazing
  • Creep
  • Crosstalk
  • Curl or Cupping
  • Delamination
  • Digital glitch or “interstitial error”
  • Distortion
  • Dropouts
  • Dub from original
  • Electromagnetic interference or RF interference
  • Embrittlement
  • Exudation
  • Flaking or Peeling
  • Flutter and Wow
  • Fungal etching
  • Gouge, Nick or Needle dig
  • Greying
  • Groove damage
  • Groove jumping
  • Hiss or Tape hiss
  • Hum or Ground hum
  • Incorrect speed
  • Longitudinal curvature
  • Low level or High level
  • Low Signal to Noise Ratio (SNR)
  • Muffled sound
  • Needle Run
  • Noise reduction artifacts
  • Pancake
  • Phasing
  • Pilot tone, SMPTE timecode
  • Pitch variations
  • Print-through or Pre-Echo / Post-Echo or Ghosting
  • Random noise
  • Rumble
  • Scrape or Scratch
  • Signal clipping
  • Sticky shed syndrome or Soft binder syndrome or Binder hydrolysis
  • Speed variations
  • Static
  • Stretch or Pull
  • Surface dirt or mold
  • Surface imprint
  • Surface noise
  • Tape squeal
  • Tape wear
  • Tape weave
  • Ticks
  • Tracing distortion
  • Vinegar syndrome
  • Warping
  • White noise

Audio Modifiers:

  • Constant
  • Heavy
  • Intense
  • Intermittent
  • Light
  • Modulating
  • Occasional
  • Periodic
  • Severe
  • Slight
  • Throughout
  • Unintelligible

Sample Audio Signal Note:

For general audio notes – select the issues that appear (steadily or sporadically) throughout the program. Set multiple notes off by a semicolon.

Buzz; Hum; Low Level; Clicks

For detailed audio notes – notes should have a time-stamp of some sort (if applicable), set off by “@”, commas, and semicolons:

Click @ 2:48; Distortion @ 0:00-11:30; Dropouts @ 10:25, 13:43, 49:51

A free text field should be available to expand on these and other issues not covered by the controlled vocabulary.

Buzz steady throughout; Occasional clicks throughout; Distortion on signal peaks

Explanation of Audio Terms:

Ambient noise: 

Ambience refers to the acoustical qualities of a listening space. Reverberation, echoes, background noise, etc., are components of ambience. On most music recordings, some of the acoustical characteristics are recorded along with the music and are to a certain extent reproduced in the listening environment. For instance, an organ in a cathedral will be recorded with a good deal of reverberation included, and this helps to provide the proper acoustic “atmosphere” when heard in playback.

Audible edit:

Magnetic tape can be cut and pasted back together with “splicing tape,” a thin piece of adhesive tape, specifically designed for splicing. When a splice is done carefully, it can be inaudible. However, even a good splice done using proper tape can break down over time. When the glue in the adhesive tape breaks down, the splice can fall off during playback or cause adjacent layers of tape to stick, often causing a brief Wow and Flutter artifact.

Bad pack:

Pack refers to the form taken by tape as it is wound on a reel or around a hub. A good tape pack will be smooth and free of ripples, buckling, cinching, etc. Common tape pack conditions that may lead to tape deformation include: step pack (or stepped pack); popped strands; flange pack; windowed tape pack; spoked tape pack; and unsecured reel end.

Blocking (layer-layer-adhesion): 

The tendency for adjacent layers of tape on a reel to stick together, usually due to long-term storage under high humidity and temperature conditions.

Broadband noise: 

A continuous distribution of energy spread over frequency. It sounds like hissing and has no detectable pitch

Buckling: 

Deformation of the circular form of a roll of magnetic tape, caused, generally, by a combination of adverse storage conditions or improper winding tension. Such deformation has a seriously detrimental effect on the quality of sound during playback.

Bubble: 

Commonly used defect term for disc recordings. It is most often the result of faulty pressing.

Bump: 

Commonly used defect term for disc recordings, implying a raised surface on a portion of the playing area of the disc which could cause sonic distortion or groove jumping by the stylus.

Buzz: 

A rasping noise heard in the background of a sound recording (disc or tape) that is generally caused by hum or noise in the playback system. In disc playback it can also be caused by imperfect or discontinuous contact of play-back stylus in the groove.

Center start disc: 

This is a disc recording (usually vertically cut) which requires the pickup and stylus to move from the center of the disc outward (having the beginning of its modulated groove at the outer edge of the inside margin). It is commonly abbreviated as C/S.

Chatter: 

An erratic “spotted” pattern in record grooves with short alternate light and dark strips. It is caused by a poor cutting stylus or one set at a wrong angle. Too deep a cut in thin disc coating may also produce a similar effect, which is most likely to occur close to the center of the record.

Chip: 

Commonly used defect term for disc or cylinder recordings. It usually refers to a small missing piece from the edge or rim of the recording, while dig or gouge refers to a pit or small break in the horizontal surface further in from the rim.

Cinching: 

Longitudinal slippage between the layers of magnetic tape in a tape pack when the roll is accelerated or decelerated. This can cause tape breakage or permanent deformation.

Clicks and Pops: 

Clicks and pops commonly manifest on disc-based media as a result of damage to the disc or contaminants contacting the stylus during playback. However, they can also show up in magnetic tape recordings that encountered static electricity buildup during tape duplication. They can originate from the source media (analog clicks) or be introduced by the digitization hardware chain (digital clicks). Clicks are higher in pitch than pops.

Coating transfer: 

Refers to the transfer of material from one layer of tape (front side) to another layer (back side) during storage in a wound pack or reel. This can cause loss of sound during playback or excess deposit (buildup) of the transferred material onto the tape heads.

Crackle: 

The distorted sound created usually because of a buildup of electrostatic charge on the surface of a sound recording, but also because of dust or foreign material permanently embedded in the grooves, or on the surface of the tape.

Crazing: 

The deformation of a laminated disc coating layer through cracking. Can be caused by loss of plasticizers, by excess heat and/or humidity, etc.

Creep:

1- The physical deformation of disc recordings due to continuous load pressure either from improper storage or from the force of gravity. It results in both surface imprint from packaging materials, which can impair fidelity by the deformation of the groove walls, and disc warpage. 2- In magnetic tape this refers to the residual deformation of the tape such as curling or longitudinal curvature which remains even after removal of tension caused by improper winding and storage.

Crosstalk: 

Undesired signal appearing in one channel as a result of leakage from another channel. In magnetic tape, it is the leakage of signal from one track to another track.

Curl / Cupping: 

On magnetic tape, a condition when the binder layer that contains magnetic information shrinks or deforms at a rate different from that of the tape base, resulting in curl of the tape.

Delamination:

The loss of adhesion between layers of a laminated cylinder, disc or tape caused by poor fabrication, exposure to fungal attack, or extremes of temperature and humidity, i.e. the peeling or flaking of the acetate layer on a lacquer disc.

Digital glitch:

An undesired voltage excursion found in a Digital-to-Analog Converter. This is due to errors in the conversion process. Often heard as a very quick digital tick, pop, or static burst.

Distortion: 

Unwanted changes of sound quality, in the frequency response, or by the generation of unwanted products. There are many different types of distortion (harmonic, intermodulation, transient, etc.). In general it can be caused by inadequate playback or recording equipment, by the poor manufacture of a sound recording, or by factors during the recording process.

Dropout analog or digital: 

Any tape-caused phenomenon that results in temporary or permanent loss or reduction of signal for a specified length of time. The most prominent cause of dropouts is surface contamination, where a piece of oxide shed or foreign particle adheres to the surface of the tape and lifts the tape from the head. Dropout can also refer to loss of signal during a radio or television broadcast, or to temporary loss of signal for electronic or electrical reasons during recording or playback. Digital audio dropout is caused by a non-uniform magnetic surface, or a malfunctioning tape deck. However, because the magnetically recorded information is in binary code, it results in a momentary loss of data and can produce a loud transient click or worse, muted audio, if the error correction scheme in the playback equipment cannot correct the error.

Dub (dubbing):

A copy of a sound recording e.g. a transfer of sound from a disc recording to magnetic tape. It can also refer to the combining of two or more recordings into a signal recording, or several tracks recorded at different times into a single recording.

Electromagnetic interference or RF interference: 

EMI is any type of interference caused by errant and unwanted electromagnetic waves that are received and amplified by an audio system. They can be picked up and recorded into an audio signal and heard upon playback of the contaminated recording. Commonly cited sources of EMI include power lines, engine ignition systems, light dimmers, as well as cell phones. Radio frequency interference (RFI) is a type of high frequency electromagnetic interference introduced by an intentional or unintentional source, such as a wireless phone, AM/FM/TV broadcast transmitters, radar systems, a microwave oven, fluorescent lights, and any number of other high frequency RF devices. An improperly shielded audio cable can act as an antenna and pick up unwanted frequencies. While the frequency spectrum of RFI interference is above the range of human hearing, “most audio circuits are nonlinear at these high frequencies, and this causes the interfering signals to be rectified, or detected.” What is heard then is not the ultrasonic frequencies, but the problems they produce.

Embrittlement: 

Shrinkage of the lacquer coating due to the loss of the castor oil plasticizer is the primary destructive force. The gradual loss of plasticizer causes progressive embrittlement and the irreversible loss of sound information. Because the coating is bonded to a core which cannot shrink, internal stresses result, which in turn cause cracking and peeling of the coating. In magnetic tape, Cellulose acetate-backed tapes are susceptible to vinegar syndrome, in which the tape base releases acetic acid, begins to shrink, and becomes brittle. The magnetic layer does not shrink, and the difference in width between the two layers causes the tape to deform (cupping).

Exudation: 

The appearance on the surface of a medium of one or several byproducts of decomposition of the medium. An example is a white powder form of palmitic acid caused by the breakdown of plasticizer in a lacquer disc.

Flaking: 

The loss of bonding or adhesion between the base and coating of laminated discs or magnetic tape, resulting in pieces of the coating breaking loose from the base. It is essentially the same as peeling but more localized in effect. Peeling describes the widespread separation of the layers.

Flutter: 

Rapid speed variations in tape or disc playback, causing pitch and/or amplitude variations. It is usually the result of faults in equipment or friction between the tape and heads or guides.

Fungal etching: 

1- The degradation or scarring of the base material in a disc or tape as a result of enzymes and acids excreted by fungi during attack on the additives in the coating. 2- Surface etching on discs or tapes resulting from excretions of fungi growing on the packaging that is in contact with the recordings.

Gouge or Nick or Needle dig: 

Commonly used defect term for disc and cylinder recordings referring to a visible pit, dig or break in the surface of the recording which will probably cause some degree of sonic distortion. It is used interchangeably with dig and needle dig.

Greying: 

Commonly used defect term for disc recordings. It indicates widespread needle wear which results in a discoloration or “greying” of a part or all of the playing area surface of the disc. It usually means the disc has been extensively played, or that it has been played with too heavy a stylus tracking weight. Sometimes called steeling .

Groove jumping:

Occurs when the pickup stylus will not remain in the groove track during playback but skips to an adjacent groove. Causes can be poor manufacture of recording, uneven playback turntable, improper tracking pressure applied to pickup, etc.

Hiss:

An undesirable wide spectrum noise heard when a recorded tape is played back. It sounds similar to a leaky steam pipe. It is caused by various factors, including taping at too low a speed, or poor quality tape. Various noise reduction systems have been developed to combat this.

Hum: 

A low frequency noise, generally related to the power-line frequency of a sound system or its harmonics, that intrudes into reproduced sound and mars the listening quality.

Incorrect speed: 

Describes gradual speed changes during media playback, either in the source recording or the transfer machine, or an incorrect playback speed chosen by the transfer engineer. The pitch of the recording will be wrong in both cases (not to be confused with Wow and Flutter).

Interstitial error: 

Coined by AudioVisual Preservation Solutions (AVPS), an interstitial error is a system “hiccup” that occurs during digitization as the data stream is being written to disk. This error results in lost samples, and it is reflected in the waveform by an abrupt vertical drop. While the audibility of these errors varies, a particularly bad one is heard as a dropout. Described in other words by Chris Lacinak, “In the middle of writing the samples of the digital stream to disk the system got “distracted”, skipped some number of samples, “remembered” it was supposed to be recording and then “came back” to continue its original task. In other words, for a short bit of time the samples were not recorded, resulting in a few “missing” milliseconds from the stream of sound. If those samples had been recorded, the line would move in an orderly way down a slope instead of making the abrupt drop…”

Longitudinal curvature: 

Deformation, usually warping or stretching, of magnetic tape along its length caused by pressure from winding the tape under tension and storing it in this condition. This is permanent deformation which impairs the reproductive sonic quality of the tape recording.

Low SNR (Signal-to-Noise Ratio): 

SNR is the ratio of the signal power at a certain reference point in a circuit to the noise power which would exist there if the signal were removed; tape noise, hum, electronic noise, etc. This ratio is expressed in decibels. This measurement ignores any type of noise which is present only when the signal is present, such as modulation noise.

Muffled sound: 

A muffled recording during playback is generally symptomatic of high frequency loss because of media failure, an incorrect wind, or a lack of high frequency information in the source recording. Unless the source is poorly recorded or the source recorder was malfunctioning during the original capture, muffled sound artifacts are the result of improper setup and playback. For instance, if azimuth is not adjusted to the source material prior to digitization, high frequencies will be lost and the resulting file will sound dull.

Needle run: 

A spiral scratch caused by the pickup stylus leaving the modulated groove and skipping across the record surface during playback. When abbreviated to NR, it is a commonly used defect indicator for disc sound recordings.

Noise reduction artifacts: 

Sonic material that is accidental or unwanted, caused by noise reduction software.

Pancake: 

A roll of magnetic tape that is wound onto a NAB hub. The roll does not have sides or flanges. Tape stored as a pancake must be handled carefully to avoid spillage as only friction holds the tape in a roll.

Phase:

Phase error as a term used to describe when certain frequencies are partially or wholly cancelled out of a recording. Phase is an issue when more than one channel is used to record a single source. Often these errors do not become evident until the recording is switched to mono. All of these things make phase error hard to identify.

Pilot tone: 

Pilot tone, a precursor of SMPTE time code, is typically encountered when working with open reel audio used in film or video production. The tone is a 50 or 60 Hz signal sent from a motion picture camera and recorded on one track of the tape. Not to be confused with hum, during production this tone was used for synchronizing tape playback to picture by matching the camera speed.1 Crosstalk is reduced by recording the tone 180 degrees out of phase with respect to the program so that it will cancel out during playback. Like hum, SMPTE time code recorded on magnetic audio tape allows for frame accurate film or video synchronization during the post-production editing process. Being a rectangular wave signal, it is heard as a pulse similar to that of a fax machine or dial-up modem. It has been described as an “obtrusive noise and often a fairly high level signal.”

Pitch variations: 

Unresolvable fast pitch changes due to batteries running low during recording, or other mechanical errors during the recording process.

Pre-Echo, Post-Echo, Ghosting:

An “echo” of a particular sound signal which, on a disc, may appear in the groove before or after that which carries the playing signal. This is due to the gradual relaxation of molecular tensions which occurs after the record has been pressed, and causes plastic deformation of the groove walls. On tape it occurs one turn of the tape before or after normal signal, and is caused by print-through.

The unwanted transfer of a magnetic field (and the sound signal) from one layer to another within a roll of tape. The magnitude of this induced signal tends to increase with the storage time and temperature and decrease with the unwinding of the tape roll. It is a function of the magnetic instability of the magnetic oxide on the tape. It causes echo or repeated sound from one layer of tape while the next layer is passing over the playback head. When tapes are stored “heads out” (oxide in), a faint echo will be heard before the main signal during playback. When tapes are stored “tails out” (oxide out), a post-echo will be heard after the main signal during playback. The post-echo is less obvious than the pre-echo, which is one of the reasons tapes should be stored tails out.

Random noise: 

Artificial noise which is intermixed and amplified with the program signal in a sound recording system, usually of electronic origin.

Rumble: 

Low frequency noise caused by the mechanism of a turntable or tape transport. Rumble sometimes can be heard from the discs themselves, having been induced during the recording or cutting stages.

Scrape: 

Commonly used defect term for sound recordings which implies a visible marring of the surface of the recording that appears to be deeper or more serious than a scuff or rub and may cause some degree of sonic distortion.

Scratch: 

Commonly used defect term for sound recordings which implies a visible marring of the surface of the recording in the form of a single, tin line or “scratch” which will cause momentary distortion (usually referred to as a tick) when the stylus tracks over it. It is markedly less severe than a crack.

Signal Clipping: 

Form of very audible distortion produced by the capabilities of an amplifier being exceeded (known as overload).

SMPTE Time Code: 

SMPTE time code recorded on magnetic audio tape allows for frame accurate film or video synchronization during the post-production editing process. Being a rectangular wave signal, it is heard as a pulse similar to that of a fax machine or dial-up modem. It has been described as an “obtrusive noise and often a fairly high level signal.” For archival purposes it is important to note the type of time code present, the frame rate, and whether it is embedded in the audio, or on a separate track.

Static: 

The distortion created in disc or tape playback when the recording has a buildup of electrostatic charge. Also refers to interference or distorted reception in a radio broadcast signal.

Sticky Shed Syndrome or Soft Binder Syndrome or Binder hydrolysis: 

A condition afflicting some polyester tape stock in which the binder on the tape stock absorbs atmospheric water (binder hydrolysis), thus weakening the bond between the substrate and the magnetic layer.

Surface imprint: 

The transfer of material from the packaging containing a recording to the surface of the recording itself due to high contact stress (caused by high temperatures, wrinkled or uneven surfaces of the packaging material, or improper and uneven storage pressure). This can result in poor playback because the transferred material may interfere with stylus tracking.

Surface noise: 

In recording playback, surface noise is the noise component in the electric output of a pickup (cartridge) due to irregularities in the contact surface of the grooves. Can be caused by many factors including dust and foreign particles in the grooves, improper stylus and pickup being used, poor manufacture, wear on the grooves caused by previous improper playback, etc.

Tape squeal: 

Commonly used term to describe the sonic distortion which occurs in playback of a tape recording which has a deterioration or loss of lubricant in its coating, causing friction as the tape passes over the playback head of the machine. It can also sometimes occur when the tape is played in an excessively dry environment.

Tape wear: 

When tape is scratched or worn from use, the magnetic material containing recorded information is easily affected, resulting in partial or complete information loss perceptible on playback. “Single, well-defined scratches should be distinguished from general mechanical wear and tear, which takes the form of many tiny scratches. Tape wear is the result of frequent playback, and is characteristic of exhibition and viewing copies”

Tape weave: 

Describes a condition in which recording tape makes unwanted up and down movement as it passes the heads. This may be caused by improper tape slitting, poor transport mechanical alignment, worn heads or tape guides, or improper winding of the tape before storage. This is also known as “country-laning”.

Tick: 

1- Commonly used defect term for sound recordings which refers to a small, visible break in the surface of the recording. It is similar to but smaller than a nick or dig. 2- Commonly used term to describe the momentary sonic distortion created when the playback stylus tracks over a defect in the surface of a recording, such as a scratch, nick, dig, etc.

Tracing distortion: 

Harmonic distortion in record playback due to improper pickup stylus tip size.

Vinegar syndrome: 

A condition afflicting acetate tape. The acetate base film chemical decomposes with age. A byproduct of the decomposition is acetic acid, the familiar smell of household vinegar. Vinegar syndrome is characterized by a sour smell and tape shrinkage and deformation.

White noise: 

1- In acetate discs, this is the increase in playback noise caused by the drying out or loss of plasticizer which creates a shrinkage of the coating, exposing nodules of imperfectly dispersed carbon black as well as minute pores. 2- Also refers to a specific type of random noise in audio equipment or recordings  where the energy content is the same at each frequency.

Wow:

Slow speed variations on a tape machine or record player (usually less than ten times a second), which cause unwanted pitch changes.