The mastering process used in pressing a vinyl album was complex, and required significant pre-processing, unlike today’s digital media. Due to the physical limitations of the LP format, some additional processing was necessary before and after the cutting of the album to achieve the best sound. The most important part of mastering for vinyl was the RIAA pre- and de-emphasis curve. This was an equalization curve that was applied to the audio as it was cut, and then the exact opposite of that curve would be applied during playback.
The curve was developed to address two limiting factors: high frequency noise and large cutter excursions during low frequencies. Records tended to have a lot of noise during playback that was concentrated in the higher frequency range. A solution to this was to roll off the high frequencies, but this also took away a lot of the shimmer and natural sound of the audio. To compensate for this, the RIAA curve boosted high frequencies by quite a bit during the cutting of the album. Then on playback, the high frequencies would be rolled off by the same amount they were boosted. This brought the music back to its original sound, and it simultaneously reduced the high frequency noise.
The same process was used for the low-end frequencies. Because lower frequencies have much larger wavelengths, they took up too much space on LP’s as they were cut, reducing the playing time available on each record. To fix this issue, the low frequencies would be rolled off during the recording. Upon playback, the low frequencies would be boosted the same amount they were rolled off, bringing the bass back to its original level. (Imagine a continuous playback equalization curve that is boosted 20 dB at 20 Hz, flat at 1,000 Hz, and attenuated 20 dB at 20,000 Hz.) The RIAA curve became an international, industry standard, ensuring that all records and record players would boost and attenuate audio frequencies appropriately.
While this was a good fix for the aforementioned problems with records, the process of dramatically boosting and cutting frequencies did not help the overall quality of the music. Lucky for us, many of the old recordings that went through this process still exist as original master tape recordings, free of the distortion introduced by applying the RIAA curve during vinyl mastering. Recently, many studios have been releasing “re-mastered” versions of classic music such as the Beatles. For those of us who really appreciate the sound quality of the music we listen to, this is great news; we can now hear some of our favorite bands the way they were originally recorded.
Interestingly, many modern bands are beginning to release their music in both digital and analog formats. Although technology has improved in the world of cutting and producing LPs, the same principles and processes apply. While most bands will give you a digital download card with your purchase of their record, there still seems to be some sentimental satisfaction in owning a vinyl version of your favorite vintage album.