Audio restoration is a subjective process, and there are many strategies or perspectives that the audio engineer or sound editor can employ. The archival perspective says that audio restoration should restore the recording to its original condition, while the commercial perspective says that the recording should be both restored and enhanced to appeal most immediately with modern audiences.
Audio restoration techniques are usually performed by digitizing an audio source from analog media, such as lacquer recordings, optical sources and magnetic tape. Once in the digital realm, recordings can be restored and cleaned up using dedicated, standalone digital processing units such as declickers, decracklers, dehissers and dialogue noise suppressors, or using digital audio workstations (DAWs). DAWs can perform various automated techniques to remove anomalies using algorithms to accomplish broadband denoising, declicking and decrackling, as well as removing buzzes and hums. Often audio engineers and sound editors use DAWs to manually remove "pops and ticks" from recordings, and the latest spectrographic 'retouching' techniques allow for the suppression or removal of discrete unwanted sounds. DAWs are capable of removing the smallest of anomalies, often without leaving artifacts and other evidence of their removal. Although fully automated solutions exist, audio restoration is sometimes a time consuming process that requires skilled audio engineers with specific experience in music and film recording techniques.
The majority of audio restoration done today is done for music sound recordings and soundtracks for motion picture and television programs. The demand for restored audio has been fueled by new media consumer technologies. Modern audio reproduction systems require that sound sources be in the best condition possible to enhance the listening experience. Media content owners have come to recognize the importance of having clean sound on their products to enhance the commercial value of their media assets.
The byproduct of these restoration efforts is that many audio sources are brought into the digital world and preserved for future use. An unfortunate fact is that most of the sound recordings and motion picture soundtracks created over the past century have been lost due to improper storage and neglect.
Enhancements are often done to motion picture soundtracks. For example taking a mono or stereo soundtrack and re-mixing it to a modern 5.1 surround soundtrack. When sources from original discrete audio "stems" containing dialog, music and sound effects are used and properly restored, the enhancements can be significant and highly effective.
REELS AND TAPES
Over time, the glue that binds the oxide to the plastic will absorb moisture and "break down." The symptoms of "binder breakdown" are immediately obvious even when rewinding. Tearing sounds and sluggish behavior are clues to quit before the oxide comes off. Machines with stationary lifters (Ampex 440/1200, MCI and 3M) will, in many cases, stall well before reaching the halfway point. An older Studer, with its rotating guides, may not reveal any warning signs until the tape is played.
Playing a bad tape is not recommended. Just trying to get through a three-minute pop song will require several cleanings. Once the precious sonic material collects on transport parts it is worthless, not to mention difficult to remove. Do you really want to risk damage to the master for the sake of getting a transfer? There is hope, so be patient.
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 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.).
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, e.g.: 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. 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.
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.