Ned Newitt (Letters, 7 February) is correct. If we are going to get technical about vinyl record reproduction (Letters, 8 February), the output of a moving coil or moving magnet cartridge is proportional to the velocity of the needle, not its position. So high frequencies produce a greater output than low frequencies and the phono amp needs to boost the bass to produce a flat frequency response. But amplifying the bass also amplifies other low-frequency components such as rumble from the turntable bearing and motor, so the deep bass often has to be sharply filtered out. The only way to get a strong deep bass is to space the grooves out on the record so that there is room for large deviations of the groove. This is admirably supplied on 12in singles where only five minutes of music takes up the space used by 30 minutes on an LP. But digital reproduction uses numbers to describe the waveform, and though the highest frequency a system can reproduce is limited by Nyquist’s theorem to half the sampling frequency, there is no theoretical reason why a digital system couldn’t reproduce bass frequencies down to zero.
Ron Bailey
Newburn, Tyne and Wear
• Doug Simpson (Letters, 8 February) may not recall that bass sounds are compressed on a vinyl record. More than 60 years ago, the Recording Industry Association of America (RIAA) set an international standard, extending the playing time of a record by de-emphasising low frequency sounds. (Higher frequency notes are boosted on a record.) The phono input restores the original sound shape.
Robin Morris
Oxford
• Join the debate – email guardian.letters@theguardian.com
• Read more Guardian letters – click here to visit gu.com/letters
