Record restoration
Encyclopedia
Record restoration, a particular kind of audio restoration
, is the process of converting the
analog signal
stored on gramophone records (either 78 rpm shellac
, or 45 and 33⅓ rpm
vinyl) into digital audio
files that can then be edited with computer software and eventually stored on a hard-drive, recorded to digital tape, or burned to a CD or DVD. The process may be divided into several separate steps performed in the following order:
1. Transcription of the record to another format on another medium (generally a digital format such as a wav file
on a computer);
2. Processing the raw sound file with software in order to remove transient noise resulting from record surface damage (clicks, pops, and crackle cause by surface scratches and wear);
3. Using software to adjust the volume and equalization;
4. Processing the audio with digital and analogue techniques to reduce surface/wideband
noise;
5. Saving the file in the desired format (WAV
, MP3
, FLAC
, etc).
The source of the information for these steps is available from various websites and the help files for the software employed in the process.
and stylus combination is used because of its superior sound characteristics and signal-to-noise ratio
over other pickup systems. The output of a magnetic cartridge is of a very low volume (typically ~5mV) so the signal must be amplified with a preamplifier
to bring it up to line level
before being routed into the line-in jack of a computer's sound card
.
Three main types of phono-preamplifier exist for the process of record restoration and playback:
Regardless of the preamplifier employed, one must ensure that the output volume is not set too high when recording through the sound card, or digital clipping
may result. A low average volume can easily be corrected later on during editing (although with some loss in dynamic range) - however, too low a volume setting can result in greater amount of noise (especially the inherent sound-card or system noise) relative to the usable audio and this noise will become prominent at the time of normalisation
of the audio. Ideally, the VU meter
should not exceed around -2 or -3dB to allow for some signal headroom. However, some clipping due to transient responses caused by scratches or cracked records are usually acceptable since these are extremely small in width and do not usually cause any audible difference. One must also be sure that all equipment is grounded appropriately together, or subtle hums will likely result from the formation of ground loops
. Similarly, the computer should have sufficient power and memory to record an entire record without any "drop-outs"— (tiny gaps in the audio stream lasting just a fraction of a second).
. Some of these applications are simple, and some are very complex. Many are general purpose waveform
editors that also happen to include record restoration features or plugins, and others are dedicated to the sole purpose of record restoration. Moreover, some applications are designed for easy fast processing with the push of a few buttons, and others require a time-consuming but perhaps more exact manual approach to editing out damage. Most applications present a waveform display, but a few are basically noise and click-pop filters that provide no visual display at all. All record restoration applications for Windows work directly upon WAV
files, but a few will also directly open files in other formats, such as MP3
.
Record restoration software normally handles 2 different categories of noise
separately. First, there is the constant background noise that goes on through the entire recording that is the result of the sound the stylus makes in the groove when no music is playing, plus whatever subtle drones are generated by the electronics involved (such as turntable rumble or 60 cycle hum). In addition to band-stop filters (also known as "notch filters"), low-pass filters, and high-pass filters for filtering out hum and noise, many applications allow the user to take a "noiseprint" of a small section of waveform when the stylus is tracking but no music is playing; the filtering is then accomplished specific to this noiseprint. Second, there are the transient bursts of damage, mostly clicks and pops, caused by scratches or record defects, and crackle caused by lots of minute defects grouped close together. The software must filter this kind of click-pop damage conservatively, because a click or a pop can look very much like a legitimate percussive effect, such as a light snare drum rim-shot. If the automatic filtering software is getting every last click, chances are good that it could also be filtering some percussion instruments. After an automatic click filtering, it is reasonable to expect a few clicks to be left over, and these must be removed manually by isolating them one-by-one in the waveform. These residual clicks may then be corrected by attenuation
(reducing or muting the volume of the anomaly), interpolation
(replacing the waveform "spike" with a less offensive section, either a straight line—linear interpolation—or a calculated facsimile deduced from what the wave looks like on either side); substitution (replacing a damaged waveform segment with a similar section from elsewhere); channel substitution (where damage occurring in only one channel of a stereo waveform is replaced by a similar good segment in the other channel); and simple deletion, which is usually not noticeable for small samples. Some applications also have a "pencil tool" with which one can actually redraw the waveform.
whereby the loudest tone in a track is amplified right up to some specified point, usually the point of digital clipping, and the rest of the waveform is amplified accordingly. In another form of amplification called "hard limiting," the loudest passages are attenuated drastically after they hit a certain limit, while the quieter passages are amplified. The result is a compressed waveform that sounds considerably louder, though it may not be what the original recording engineers intended. In all of these volume adjustments, one should respect the original dynamics of a piece, and of the variation in dynamics among different tracks in the same LP.
In addition to adjusting the volume, at this point one may desire to adjust the frequency profile of a piece with the "graphic equalizer" that is normally supplied with a wave editor. Some might feel that a track needs a slight treble boost, or reduction, or a big boost in the bass department. One should satisfy one's own perception of what sounds best for any particular track. An application usually lets you "preview" a piece before applying the equalization
effects.
form, and some can also save files as MP3
, FLAC
, or in other formats. Many CD-R
burning applications can then take these files and burn them onto a blank recordable disc in a form that can be played on a common CD player (using the standard CD-DA format).
(This "gradual degradation" is more noticeable on some discs than others. In fact it is possible to have eighty year old records that sound as new as brand new discs with pops and tics. How the records are handled and the equipment on which they are played as well as the manufacturing process and quality of original vinyl have a considerable impact upon their wear.)
Where old disc recordings are considered to be of artistic or historic interest, record companies or archivists play back the disc on suitable equipment and record the result, typically onto a digital format which can be copied and converted without any further damage to the recording. For example, Nimbus Records
uses a specially built horn record player to transfer 78s. However, anyone can do this using a standard record player with a suitable pickup, a phono-preamp (pre-amplifier) and a typical personal computer. Once a recording has been digitized, it can be manipulated with software to restore and, hopefully, improve the sound, for example by removing the result of scratches. It can also be easily converted to other digital formats such as DVD-A, CD and MP3
.
As an alternative to playback with a stylus, a recording can be read optically, processed with software that calculates the velocity that the stylus would be moving in the mapped grooves and converted to a digital recording
format. This does no further damage to the disc and generally produces a better sound than normal playback. This technique also has the potential to allow for reconstruction of damaged or broken disks.
With regard to inner sleeves, plastic polyethylene is purported to be better than the common paper sleeve and less bulky than the poly-lined paper variety. Paper sleeves deteriorate over time, leave dusty fibers, and produce static that attract dust. 100% poly sleeves produce less static (thereby attracting less dust), are archival, and are thinner by nature so they minimize pressure on the LP jacket seams.
Audio restoration
Audio restoration is a generalized term for the process of removing imperfections from sound recordings. Audio restoration can be performed directly on the recording medium , or on a digital representation of the recording using a computer...
, is the process of converting the
analog signal
Analog signal
An analog or analogue signal is any continuous signal for which the time varying feature of the signal is a representation of some other time varying quantity, i.e., analogous to another time varying signal. It differs from a digital signal in terms of small fluctuations in the signal which are...
stored on gramophone records (either 78 rpm shellac
Shellac
Shellac is a resin secreted by the female lac bug, on trees in the forests of India and Thailand. It is processed and sold as dry flakes , which are dissolved in ethyl alcohol to make liquid shellac, which is used as a brush-on colorant, food glaze and wood finish...
, or 45 and 33⅓ rpm
vinyl) into digital audio
Digital audio
Digital audio is sound reproduction using pulse-code modulation and digital signals. Digital audio systems include analog-to-digital conversion , digital-to-analog conversion , digital storage, processing and transmission components...
files that can then be edited with computer software and eventually stored on a hard-drive, recorded to digital tape, or burned to a CD or DVD. The process may be divided into several separate steps performed in the following order:
1. Transcription of the record to another format on another medium (generally a digital format such as a wav file
WAV
Waveform Audio File Format , is a Microsoft and IBM audio file format standard for storing an audio bitstream on PCs...
on a computer);
2. Processing the raw sound file with software in order to remove transient noise resulting from record surface damage (clicks, pops, and crackle cause by surface scratches and wear);
3. Using software to adjust the volume and equalization;
4. Processing the audio with digital and analogue techniques to reduce surface/wideband
Wideband
In communications, wideband is a relative term used to describe a wide range of frequencies in a spectrum. A system is typically described as wideband if the message bandwidth significantly exceeds the channel's coherence bandwidth....
noise;
5. Saving the file in the desired format (WAV
WAV
Waveform Audio File Format , is a Microsoft and IBM audio file format standard for storing an audio bitstream on PCs...
, MP3
MP3
MPEG-1 or MPEG-2 Audio Layer III, more commonly referred to as MP3, is a patented digital audio encoding format using a form of lossy data compression...
, FLAC
FLAC
FLAC is a codec which allows digital audio to be losslessly compressed such that file size is reduced without any information being lost...
, etc).
The source of the information for these steps is available from various websites and the help files for the software employed in the process.
Hardware
The first step involves transcription of a record using a suitable turntable and a suitable cartridge-stylus combination. More often than not, a magnetic cartridgeMagnetic cartridge
A magnetic cartridge is a transducer used for the playback of gramophone records on a turntable or phonograph. It converts mechanical vibrational energy from a stylus riding in a spiral record groove into an electrical signal that is subsequently amplified and then converted back to sound by a...
and stylus combination is used because of its superior sound characteristics and signal-to-noise ratio
Signal-to-noise ratio
Signal-to-noise ratio is a measure used in science and engineering that compares the level of a desired signal to the level of background noise. It is defined as the ratio of signal power to the noise power. A ratio higher than 1:1 indicates more signal than noise...
over other pickup systems. The output of a magnetic cartridge is of a very low volume (typically ~5mV) so the signal must be amplified with a preamplifier
Preamplifier
A preamplifier is an electronic amplifier that prepares a small electrical signal for further amplification or processing. A preamplifier is often placed close to the sensor to reduce the effects of noise and interference. It is used to boost the signal strength to drive the cable to the main...
to bring it up to line level
Line level
Line level is a term used to denote the strength of an audio signal used to transmit analog sound between audio components such as CD and DVD players, TVs, audio amplifiers, and mixing consoles, and sometimes MP3 players....
before being routed into the line-in jack of a computer's sound card
Sound card
A sound card is an internal computer expansion card that facilitates the input and output of audio signals to and from a computer under control of computer programs. The term sound card is also applied to external audio interfaces that use software to generate sound, as opposed to using hardware...
.
Three main types of phono-preamplifier exist for the process of record restoration and playback:
- those that apply RIAA equalizationRIAA equalizationRIAA equalization is a specification for the correct recording of gramophone records, established by the Recording Industry Association of America...
or RIAA de-emphasis on playback to counteract the equalization used when the recording was originally made. These are generally not suitable for 78rpm records and early microgroove recordings. - those that include a switchable frequency turnover filter to match the various turnover frequencies used by the many record manufacturers between 1925 and ~1960.
- those that apply no equalization (also called "Flat" phonopreamplifiers). These require audio software to apply the correct equalization to the digital recording during the restoration process. As such, this type of premplifier is suitable for all record formats regardless of equalization employed by the mastering process.
Regardless of the preamplifier employed, one must ensure that the output volume is not set too high when recording through the sound card, or digital clipping
Clipping (audio)
Clipping is a form of waveform distortion that occurs when an amplifier is overdriven and attempts to deliver an output voltage or current beyond its maximum capability...
may result. A low average volume can easily be corrected later on during editing (although with some loss in dynamic range) - however, too low a volume setting can result in greater amount of noise (especially the inherent sound-card or system noise) relative to the usable audio and this noise will become prominent at the time of normalisation
Audio normalization
Audio normalization is the application of a constant amount of gain to an audio recording in order to bring the average or peak amplitude to a target level ....
of the audio. Ideally, the VU meter
VU meter
A VU meter is often included in audio equipment to display a signal level in Volume Units; the device is sometimes also called volume indicator ....
should not exceed around -2 or -3dB to allow for some signal headroom. However, some clipping due to transient responses caused by scratches or cracked records are usually acceptable since these are extremely small in width and do not usually cause any audible difference. One must also be sure that all equipment is grounded appropriately together, or subtle hums will likely result from the formation of ground loops
Ground loop (electricity)
In an electrical system, a ground loop usually refers to a current, almost always unwanted, in a conductor connecting two points that are supposed to be at the same potential, often ground, but are actually at different potentials. Ground loops created by improperly designed or improperly installed...
. Similarly, the computer should have sufficient power and memory to record an entire record without any "drop-outs"— (tiny gaps in the audio stream lasting just a fraction of a second).
Software
The software used to process the resulting digital files ranges in price from thousands of dollars to freewareFreeware
Freeware is computer software that is available for use at no cost or for an optional fee, but usually with one or more restricted usage rights. Freeware is in contrast to commercial software, which is typically sold for profit, but might be distributed for a business or commercial purpose in the...
. Some of these applications are simple, and some are very complex. Many are general purpose waveform
Waveform
Waveform means the shape and form of a signal such as a wave moving in a physical medium or an abstract representation.In many cases the medium in which the wave is being propagated does not permit a direct visual image of the form. In these cases, the term 'waveform' refers to the shape of a graph...
editors that also happen to include record restoration features or plugins, and others are dedicated to the sole purpose of record restoration. Moreover, some applications are designed for easy fast processing with the push of a few buttons, and others require a time-consuming but perhaps more exact manual approach to editing out damage. Most applications present a waveform display, but a few are basically noise and click-pop filters that provide no visual display at all. All record restoration applications for Windows work directly upon WAV
WAV
Waveform Audio File Format , is a Microsoft and IBM audio file format standard for storing an audio bitstream on PCs...
files, but a few will also directly open files in other formats, such as MP3
MP3
MPEG-1 or MPEG-2 Audio Layer III, more commonly referred to as MP3, is a patented digital audio encoding format using a form of lossy data compression...
.
Record restoration software normally handles 2 different categories of noise
Noise
In common use, the word noise means any unwanted sound. In both analog and digital electronics, noise is random unwanted perturbation to a wanted signal; it is called noise as a generalisation of the acoustic noise heard when listening to a weak radio transmission with significant electrical noise...
separately. First, there is the constant background noise that goes on through the entire recording that is the result of the sound the stylus makes in the groove when no music is playing, plus whatever subtle drones are generated by the electronics involved (such as turntable rumble or 60 cycle hum). In addition to band-stop filters (also known as "notch filters"), low-pass filters, and high-pass filters for filtering out hum and noise, many applications allow the user to take a "noiseprint" of a small section of waveform when the stylus is tracking but no music is playing; the filtering is then accomplished specific to this noiseprint. Second, there are the transient bursts of damage, mostly clicks and pops, caused by scratches or record defects, and crackle caused by lots of minute defects grouped close together. The software must filter this kind of click-pop damage conservatively, because a click or a pop can look very much like a legitimate percussive effect, such as a light snare drum rim-shot. If the automatic filtering software is getting every last click, chances are good that it could also be filtering some percussion instruments. After an automatic click filtering, it is reasonable to expect a few clicks to be left over, and these must be removed manually by isolating them one-by-one in the waveform. These residual clicks may then be corrected by attenuation
Attenuation
In physics, attenuation is the gradual loss in intensity of any kind of flux through a medium. For instance, sunlight is attenuated by dark glasses, X-rays are attenuated by lead, and light and sound are attenuated by water.In electrical engineering and telecommunications, attenuation affects the...
(reducing or muting the volume of the anomaly), interpolation
Interpolation
In the mathematical field of numerical analysis, interpolation is a method of constructing new data points within the range of a discrete set of known data points....
(replacing the waveform "spike" with a less offensive section, either a straight line—linear interpolation—or a calculated facsimile deduced from what the wave looks like on either side); substitution (replacing a damaged waveform segment with a similar section from elsewhere); channel substitution (where damage occurring in only one channel of a stereo waveform is replaced by a similar good segment in the other channel); and simple deletion, which is usually not noticeable for small samples. Some applications also have a "pencil tool" with which one can actually redraw the waveform.
Volume and equalization
After the noise and clicks and pops have been removed, one may adjust the volume. This is usually done by a process called audio normalizationAudio normalization
Audio normalization is the application of a constant amount of gain to an audio recording in order to bring the average or peak amplitude to a target level ....
whereby the loudest tone in a track is amplified right up to some specified point, usually the point of digital clipping, and the rest of the waveform is amplified accordingly. In another form of amplification called "hard limiting," the loudest passages are attenuated drastically after they hit a certain limit, while the quieter passages are amplified. The result is a compressed waveform that sounds considerably louder, though it may not be what the original recording engineers intended. In all of these volume adjustments, one should respect the original dynamics of a piece, and of the variation in dynamics among different tracks in the same LP.
In addition to adjusting the volume, at this point one may desire to adjust the frequency profile of a piece with the "graphic equalizer" that is normally supplied with a wave editor. Some might feel that a track needs a slight treble boost, or reduction, or a big boost in the bass department. One should satisfy one's own perception of what sounds best for any particular track. An application usually lets you "preview" a piece before applying the equalization
Equalization
Equalization, is the process of adjusting the balance between frequency components within an electronic signal. The most well known use of equalization is in sound recording and reproduction but there are many other applications in electronics and telecommunications. The circuit or equipment used...
effects.
Export and save
After all this is done, the file (or files) are ready to export (or save) in whatever form the user desires. Almost all wave editing applications have the default ability to save files in WAVWAV
Waveform Audio File Format , is a Microsoft and IBM audio file format standard for storing an audio bitstream on PCs...
form, and some can also save files as MP3
MP3
MPEG-1 or MPEG-2 Audio Layer III, more commonly referred to as MP3, is a patented digital audio encoding format using a form of lossy data compression...
, FLAC
FLAC
FLAC is a codec which allows digital audio to be losslessly compressed such that file size is reduced without any information being lost...
, or in other formats. Many CD-R
CD-R
A CD-R is a variation of the Compact Disc invented by Philips and Sony. CD-R is a Write Once Read Many optical medium, though the whole disk does not have to be entirely written in the same session....
burning applications can then take these files and burn them onto a blank recordable disc in a form that can be played on a common CD player (using the standard CD-DA format).
Preservation
Each medium - including digital media - has benefits and drawbacks and over the long term, vinyl records may even have advantages over digital media. Due to the nature of the medium, playback of "hard" records, eg: LPs, causes gradual degradation of the recording. CDs, however, can also have degradation due to "CD rot" and other abnormalities. CDs' shelf life has been disputed as to whether it is to be the equivalent of vinyl- which actually can last for years of playback. CDs also can have shortcomings such as skips and clicks. This is due to problems with the laser reading the discs. On the other hand, a vinyl record will play under most any circumstance because it is an analog medium. The recordings are best preserved by transferring them onto more stable media and playing the records as rarely as possible. They need to be stored on edge, and do best under environmental conditions that most humans would find comfortable. The medium needs to be kept clean — but alcohol should only be used on PVC or optical media, not on 78s. The equipment for playback of certain formats (e.g. 16 and 78 rpm) is manufactured only in small quantities, leading to increased difficulty in finding equipment to play the recordings.(This "gradual degradation" is more noticeable on some discs than others. In fact it is possible to have eighty year old records that sound as new as brand new discs with pops and tics. How the records are handled and the equipment on which they are played as well as the manufacturing process and quality of original vinyl have a considerable impact upon their wear.)
Where old disc recordings are considered to be of artistic or historic interest, record companies or archivists play back the disc on suitable equipment and record the result, typically onto a digital format which can be copied and converted without any further damage to the recording. For example, Nimbus Records
Nimbus Records
Nimbus Records is a British record company specializing in classical music recordings.Nimbus was founded in 1972 by the late bass singer Numa Labinsky and the brothers Michael and Gerald Reynolds and has traditionally been based at the Wyastone Leys mansion site, near Monmouth and the English/Welsh...
uses a specially built horn record player to transfer 78s. However, anyone can do this using a standard record player with a suitable pickup, a phono-preamp (pre-amplifier) and a typical personal computer. Once a recording has been digitized, it can be manipulated with software to restore and, hopefully, improve the sound, for example by removing the result of scratches. It can also be easily converted to other digital formats such as DVD-A, CD and MP3
MP3
MPEG-1 or MPEG-2 Audio Layer III, more commonly referred to as MP3, is a patented digital audio encoding format using a form of lossy data compression...
.
As an alternative to playback with a stylus, a recording can be read optically, processed with software that calculates the velocity that the stylus would be moving in the mapped grooves and converted to a digital recording
Digital recording
In digital recording, digital audio and digital video is directly recorded to a storage device as a stream of discrete numbers, representing the changes in air pressure for audio and chroma and luminance values for video through time, thus making an abstract template for the original sound or...
format. This does no further damage to the disc and generally produces a better sound than normal playback. This technique also has the potential to allow for reconstruction of damaged or broken disks.
With regard to inner sleeves, plastic polyethylene is purported to be better than the common paper sleeve and less bulky than the poly-lined paper variety. Paper sleeves deteriorate over time, leave dusty fibers, and produce static that attract dust. 100% poly sleeves produce less static (thereby attracting less dust), are archival, and are thinner by nature so they minimize pressure on the LP jacket seams.
External links
- The Wave Corrector Tutorial
- A Technical Overview
- RecordRestoration.com - General Info & Tutorials
- Preserving vinyl records digitally Site has some relevant video content.
- Converting gramophone and analogue recordings to mp3. A practical step-by-step guide.
- Transferring LP's to CDR
- Restoring Old Gramophone Records
- Links to software vendors
- Popular open source software used to transfer analogue to digital