Session Notes - The Vinyl Frontier (Part 2 preparing audio for vinyl)
Hello PVC lovers. Vinyl is a very difficult beast to tame. It is very temperamental and can get quite upset at the slightest deviation from its comfort zone. In order to keep it happy it is always best to treat it with the respect it deserves. This means preparing your audio masters in accordance with vinyl’s very stringent requirements. The frequency response of vinyl records can reach 50Khz and go as low as 20Hz. The masters for vinyl cutting will rarely (if ever) exceed this limit. The dynamic range for vinyl can vary between 60db - 70db. Masters submitted for vinyl cutting will almost always exceed this limit. So let’s begin with the frequency response.
I always filter the frequency extremes to give the cutting head a chance to accurately cut the groove. Remember that the groove is the “plastic sculpture” of the waveform that once resided in the air before being captured by a microphone. Or the waveform on your screen if you DI’d (direct injection) the sound from a synth, for example.
The cutting head heats up dramatically with super high frequencies so I tend to execute an LPF (Low Pass Filter) at the top end to reduce the severity of super high frequencies. Conversely, I use an HPF (High Pass Filter) to remove super low frequencies that the cutting head and eventually the turntable stylus will have difficulty tracking. I use filters with a characteristic of between 6db & 12db per octave. I shan’t reveal the exact frequencies I use because that is one of my unique practices. But do try this yourselves by all means: it cleans up and tightens the sound in a rather pleasing way.
Another technique I use is to ‘mono-ise’ (new word there) the bass frequencies below a certain point. Cutting heads like linear centred bass waveforms. Bass causes the cutting head on the lathe to move from side to side greater than other frequencies. Too much bass or stereo bass at high amplitude can cause the groove to cut into the preceding groove causing a skip on the record which will become apermanent feature on the disc, it will also cut your playing time.
Interestingly, one second of music on a 12” LP @ 331⁄3 rpm starting at the beginning has a groove length of around 18 inches. At the end of the side the groove length is around 8 inches long, so imagine trying to cram all that frequency information that once occupied 18 inches into 8 inches. The end of a vinyl LP side is where the frequency response really suffers as a result of this. It is known as ‘inner groove distortion’ and has nothing to do with people who have difficulty dancing. Also there is the RIAA (Recording Industry Association of America) equalisation curve, introduced in the late 1940s. The equalisation curve is applied at the lacquer cutting stage and works like this: bass content is reduced and treble is increased. The bass frequencies take up so much space that you wouldn’t be able to get more than five minutes per side and the treble increase greatly reduces surface noise. On playback this is reversed at the phono preamp thereby restoring the original frequency content.
One other thing that’s very important is sibilance. Sibilance (a distortion of high frequencies) is usually caused by vocal artefacts based around the letter ’Sssss’. These high frequency distortions sound God awful on most playback media but none moreso than vinyl. So make sure that you ‘De-Ess’ your vocals if your music is destined for vinyl. Any kind of harshness from cymbals, vocals, hi synth parts etc sound atrocious when committed to vinyl untamed. So ... please address the top end of your mixes.
One of the most overlooked criteria for vinyl records is the side length. The maximum length for a 12” LP @ 331⁄3 rpm is 22-24 mins. At 45rpm it’s about 15 mins. For 7” singles @ 45 rpm it’s 6 mins. I’ve lost count of the number of times a band has requested vinyl masters for their album that’s coming in at 60 mins. For CD that’s fine ... for vinyl ... NO CHANCE ... you’re gonna have to lose some tracks and that is that or run to a double album. The running time will
dictate the ‘loudness’ of the cut and if you have frequency extremes (especially the bass) you’re going to run into serious problems.
Next month I’ll look at aspects of dynamic range, levels and stereo.