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Record restoration
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Record restoration
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 33+1⁄3 rpm vinyl) into digital audio files that can then be edited with computer software and digitally stored. The process may be divided into several separate steps performed in the following order:
The source of the information for these steps is available from various websites and the help files for the software employed in the process.
The first step involves cleaning the playing surface of the records (unless they have been stored in archival, dust-free conditions since they were last cleaned). This can involve anything from turntable-based, vacuum-equipped, professional cleaning machines that use proprietary chemical formulations and cost four figures, to improvised methods involving home-made equipment and/or cleaning solutions consisting of isopropyl alcohol, distilled water (unpurified tap water should not be used, as it will probably leave limescale deposits on the record surface) and a surfactant to aid drying. Isopropyl alcohol should only be used to clean vinyl records: it will cause permanent damage to shellac, master and one-time recordings (acetate, wax and lacquer).
The second step involves transcription of a record using a suitable turntable and a suitable cartridge-stylus combination. More often than not, a magnetic cartridge 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. Sound cards made specifically for digitally recording vinyl (as well as those designed for DJing with timecode vinyl) have phono preamplifiers built in, eliminating the need for two separate devices.
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 -3 dB 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).
The software used to process the resulting digital files ranges in price from thousands of dollars to freeware. 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. Most commonly this type of audio processing is now done via a DAW.
Record restoration software normally handles two 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 50/60 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 many 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.
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Record restoration
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 33+1⁄3 rpm vinyl) into digital audio files that can then be edited with computer software and digitally stored. The process may be divided into several separate steps performed in the following order:
The source of the information for these steps is available from various websites and the help files for the software employed in the process.
The first step involves cleaning the playing surface of the records (unless they have been stored in archival, dust-free conditions since they were last cleaned). This can involve anything from turntable-based, vacuum-equipped, professional cleaning machines that use proprietary chemical formulations and cost four figures, to improvised methods involving home-made equipment and/or cleaning solutions consisting of isopropyl alcohol, distilled water (unpurified tap water should not be used, as it will probably leave limescale deposits on the record surface) and a surfactant to aid drying. Isopropyl alcohol should only be used to clean vinyl records: it will cause permanent damage to shellac, master and one-time recordings (acetate, wax and lacquer).
The second step involves transcription of a record using a suitable turntable and a suitable cartridge-stylus combination. More often than not, a magnetic cartridge 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. Sound cards made specifically for digitally recording vinyl (as well as those designed for DJing with timecode vinyl) have phono preamplifiers built in, eliminating the need for two separate devices.
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 -3 dB 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).
The software used to process the resulting digital files ranges in price from thousands of dollars to freeware. 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. Most commonly this type of audio processing is now done via a DAW.
Record restoration software normally handles two 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 50/60 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 many 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.