The following equipment will be needed to produce a signal capable of being digitised in your PC:
- a turntable and pickup arm fitted with a good quality cartridge and stylus
- a pre-amplifier with RIAA equalisation
- a PC with either on-board sound capability or an add-in sound card
- interconnecting cables
There are a number of problems associated with the digitisation of 78rpm record:
- Turntables capable of playing 78rpm records are not easy to find these days. Moreover, since not all 78rpm records were actually recorded at the same speed, it’s desirable to use a deck that has a speed range of between 67 and 85rpm (although a range of between 72 and 82rpm will be sufficient for the majority of records).
- You can’t use a stylus intended for the playback of a modern microgroove record for 78rpm records, since the latter have much wider grooves. At the time the format became obsolete, the recommended stylus size was 2.5 thousandths of an inch conical. In practice, the optimal stylus size and shape varies from record to recording. Generally elliptical styli are better than spherical. Also, a truncated stylus (one that is flattened off at the bottom) will generally achieve a better result, since it’s able to pick up the relatively unworn part of the groove.
- 78rpm records pre-date the RIAA equalisation curve, meaning that you can’t connect the deck to the phono connector of your amplifier. The easiest solution to this is to re-equalise using an audio package with a graphic equaliser to achieve a more convincing frequency response.
Consequently, the easiest solution may be to use one of the many companies who offer specialist 78rpm-to-CD conversion services.
In a magnetic phono cartridge, the playback stylus is attached to a magnet placed in close proximity to a coil of wire. The cartridge acts as a transducer, converting the magnet’s mechanical vibrations in the record groove into an electrical signal in the coil. Magnetic cartridges are velocity-sensitive transducers, generally producing a signal of the order of a few millivolts, several hundred times too small to feed into most PC sound cards. Ideally your cartridge should have a frequency response of between 20 and 20,000Hz with a loss in the region of 2dB at either end of the range.
A pre-amplifier is required to amplify the low level signal from the phono cartridge to a suitable level (~1volt) for input to the PC and to provide the correct RIAA equalisation to ensure a flat frequency response from the record. Many hi-fi systems integrate the pre- and power amplifiers into a single unit. Provided this has a signal-to-noise ratio of at least 60 decibels, it can be used to feed the PC’s soundcard from the output intended for tape recording.
If necessary, you will have purchase a specialist pre-amp. These stand-alone devices generally offer the advantage of an adjustable output level. As well as the more obvious sources such as specialist hi-fi retailers and DIY electronics outlets, they are also now available from some soundcard and even audio editing software manufacturers.
Where the source audio signals are generated by a transducer – as is the case with an analogue vinyl LP disc – the maximum signal level is of the order of only 10s of millivolts. Moreover, since the available dynamic range of a vinyl LP disc is significantly lower than that of the music to be recorded, a technique of pre-emphasis during the recording process is employed (RIAA equalisation) to enhance this dynamic range. This cuts lower frequencies in the process. It also allows the width of grooves – which would otherwise be difficult for a stylus to follow – to be reduced, thereby increasing the recording time available on a disc. As a result, the frequency spectrum of the signal generated from a vinyl disc is not flat, the recorded amplitude varying as a function of frequency.
The RIAA curve is a set standard for frequency response of filters used when playing back vinyl recordings, used to restore lower frequencies that were reduced at the recording stage. A pre-amp’s principal function in the digitisation of vinyl recorded material is to provide both the gain to match the other line level sources and to apply the equalisation to convert the signal back to the original music spectrum.
Audio recording isn’t a particularly demanding task, so any PC bought since the turn of the millennium should be easily up to the task. The CD specification requires that it be capable of recording sound in 16bit stereo at 44.1KHz. This will be within the scope of any add-in sound card or even a PC with integrated sound capability.
A more powerful PC will come into its own when you come to edit and manipulate your digitised sound. The more powerful your processor the better, since the kinds of waveform transformations required to clean up your audio are very CPU-intensive. Uncompressed .wav audio files occupying about 10MB/min, so it’s equally important to maximise the amount of RAM available and hard disk storage space.
You’ll obviously need a CD burner. Note that the speed of a leading-edge drive is likely to outstrip that of the most widely available – and most reasonably priced – media.
Assuming you’re using your existing hi-fi equipment to connect your turntable to your pre-amp unit, the only additional cable you’ll need is for connecting your pre-amp to PC soundcard. Most PC soundcards utilise a 3.5mm jack as the line input connector and most hi-fi equipment uses RCA type sockets for connecting audio components. Y connectors, with two RCA plugs at one end and a single, stereo 3.5mm jack at the other (also called a stereo RCA-to-headphone cable) are readily available.
Assuming you’re using your existing hi-fi equipment to connect your turntable to your pre-amp unit, the only additional cable you’ll need is for connecting your pre-amp to PC soundcard.
If possible, use a cable 1m or less in length, to keep signal noise to a minimum