The Recording Chain Setting the Record Level Introduction Playing vinyl for digital re-mastering is a little different from playing for normal listening.
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You will want too ensure absolute optimum quality because any imperfections at this stage will be permanently incorporated into your CD-R copy. You may, for example, decide to play using a slightly higher than normal tracking force since the additional wear to the vinyl is outweighed by the improved noise and distortion characteristics attained. Equipment needed The following equipment will be needed to produce a signal capable of driving a typical multimedia PC soundcard. A turntable and pickup arm fitted with a good quality cartridge and stylus.
Interconnecting cables. This means that the turntable must be positioned on a solid level surface free from vibration. The pickup arm should be inspected to ensure that the cartridge is correctly installed for minimum horizontal tracking error and the correct playing weight. The cartridge manufacturer will specify a range of playing weights. For mastering, it is advisable to set this adjustment near the maximum recommended value.
Having set the playing weight, you should then ensure that the side thrust anti-skating adjustment is correctly set. The arm manufacturer will have provided instructions for making these adjustments. Your pickup arm will probably have been supplied with a cartridge to suit the characteristics of the arm.
AUDIO FORMAT TRANSFERS
If you choose to change the cartridge, it is important to ensure that the compliance of the replacement cartridge matches the arm. Otherwise unwanted resonances can severely compromise quality. If a low compliance cartridge is fitted to a high compliance arm then the tracking performance will be impaired, particularly during loud sections of music.
Conversely, a high compliance cartridge fitted to a low compliance arm will result in mis-tracking if the record is not perfectly flat. Additionally, a large sub-audio signal will be generated due to the undulating motion of the cartridge over a non-flat record. Stylus Maintenance One of the most common causes of audio distortion when playing vinyl is contamination of the stylus.
The contamination occurs when surface dust gradually accumulates on the stylus during play causing the distortion to get progressively worse. Record Cleaning A vinyl record must be as clean as possible to achieve optimum audio quality. The main reason for cleaning a record before each play is to remove surface dust which would otherwise accumulate on the stylus and impair the sound.
This also helps to reduce static and reduces the further accumulation of surface dust. Interconnecting Equipment Most PC soundcards utilise a 3. Conversely, most hi-fi equipment uses either phono or DIN connectors. You will therefore need to fabricate or purchase a connecting lead which converts between the two connector standards.
Throughout this section, you will be advised at several points to make test recordings to verify audio quality.
- Restoration & Transfer.
- How to Record Vinyl to Your Computer With Audacity.
- Vinyl Records and Cassettes.
In this way, you can be sure that your results will be as good as possible. This is particularly important if you are going to use audio restoration software to process your recordings.
The magnitude of this noise or distortion is determined by the number of quantization levels. In binary systems this is determined by and typically stated in terms of the number of bits. Rumble is a form of noise characteristic caused by imperfections in the bearings of turntables, the platter tends to have a slight amount of motion besides the desired rotation—the turntable surface also moves up-and-down and side-to-side slightly.
This additional motion is added to the desired signal as noise, usually of very low frequencies, creating a rumbling sound during quiet passages. Very inexpensive turntables sometimes used ball bearings which are very likely to generate audible amounts of rumble. More expensive turntables tend to use massive sleeve bearings which are much less likely to generate offensive amounts of rumble. Increased turntable mass also tends to lead to reduced rumble. Wow and flutter are a change in frequency of an analog device and are the result of mechanical imperfections, with wow being a slower rate form of flutter.
Wow and flutter are most noticeable on signals which contain pure tones. For LP records, the quality of the turntable will have a large effect on the level of wow and flutter. A good turntable will have wow and flutter values of less than 0. Owing to their use of precision crystal oscillators for their timebase , digital systems are not subject to wow and flutter. For digital systems, the upper limit of the frequency response is determined by the sampling frequency. The choice of sample sampling frequency in a digital system is based on the Nyquist-Shannon sampling theorem.
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This states that a sampled signal can be reproduced exactly as long as it is sampled at a frequency greater than twice the bandwidth of the signal, the Nyquist frequency. The sampling theorem also requires that frequency content above the Nyquist frequency be removed from the signal to be sampled.
This is accomplished using anti-aliasing filters which require a transition band to sufficiently reduce aliasing. Unlike the audio CD, vinyl records and cassettes do not require anti-aliasing filters. The low frequency response of vinyl records is restricted by rumble noise described above , as well as the physical and electrical characteristics of the entire pickup arm and transducer assembly. The high frequency response of vinyl depends on the cartridge.
Digital systems require that all high frequency signal content above the Nyquist frequency must be removed prior to sampling, which, if not done, will result in these ultrasonic frequencies "folding over" into frequencies which are in the audible range, producing a kind of distortion called aliasing. Aliasing is prevented in digital systems by an anti-aliasing filter.
However, designing a filter which precisely removes all frequency content exactly above or below a certain cutoff frequency, is impractical. This solution is called oversampling , and allows a less aggressive and lower-cost anti-aliasing filter to be used. Early digital systems may have suffered from a number of signal degradations related to the use of analog anti-aliasing filters, e.
The digital filter can be made to have a near-ideal transfer function, with low in-band ripple, and no aging or thermal drift. Analog systems are not subject to a Nyquist limit or aliasing and thus do not require anti-aliasing filters or any of the design considerations associated with them. Sampling the waveform at higher frequencies and allowing for a greater number of bits per sample allows noise and distortion to be reduced further.
With any of these sampling rates, signal information is captured above what is generally considered to be the human hearing range. Work done in by Muraoka et al. This demonstrates that presence or absence of ultrasonic content does not explain aural variation between sample rates. He posits that variation is due largely to performance of the band-limiting filters in converters. These results suggest that the main benefit to using higher sample rates is that it pushes consequential phase distortion from the band-limiting filters out of the audible range and that, under ideal conditions, higher sample rates may not be necessary.
A signal is recorded digitally by an analog-to-digital converter , which measures the amplitude of an analog signal at regular intervals specified by the sampling rate, and then stores these sampled numbers in computer hardware. The fundamental problem with numbers on computers is that the range of values that can be represented is finite, which means that during sampling, the amplitude of the audio signal must be rounded to the nearest representation.
This process is called quantization, and these small errors in the measurements are manifested aurally as low level noise or distortion. This form of distortion, sometimes called granular or quantization distortion, has been pointed to as a fault of some digital systems and recordings particularly some early digital recordings, where the digital release was said to be inferior to the analog version.
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The range of possible values that can be represented numerically by a sample is determined by the number of binary digits used. This is called the resolution, and is usually referred to as the bit depth in the context of PCM audio. The quantization noise level is directly determined by this number, decreasing exponentially linearly in dB units as the resolution increases. With an adequate bit depth, random noise from other sources will dominate and completely mask the quantization noise. Analog systems do not necessarily have discrete digital levels in which the signal is encoded.