07 Consumer audio formats

Vinyl records

Singles were played at 45 RPM and albums at 33 1/3 RPM (revolutions per minute); a faster RPM = better quality
Pressing a record starts with a master disc having grooves cut into it; these are small bumps that are a physical representation of the music’s waveform starting at the outside of the record and leading into the centre
Each side of the groove corresponds to a separate side of the stereo image
On playing back a record, a stylus then moves in a groove as the disc is rotated and the vibrations are converted into an electrical signal – this is then amplified and played through speakers
Audio signals are cut into the vinyl master with a reduced low end and boosted highs, so turntables have an inverse EQ curve (RIAA curve) which results in a flat frequency response on playback
Until the late 60s, albums had both a mono and stereo release; artists focussed on mono / stereo was a gimmick
Advantages – ‘warm’ sound; there has been a recent resurgence in popularity – with this in mind, bands sometimes still release on vinyl for kudos and record sleeve artwork is appreciated by fans
Disadvantages – sound quality deteriorates towards the centre of the record as the grooves are packed closer together; sound affected by scratches / dust / warping / wow & flutter and prone to rumble; not very portable.

The cassette as a consumer product was launched by Phillips in 1961 but took a while to catch on
Cassettes began to overtake vinyl in popularity because they suffered from fewer audio issues than vinyl
An analogue representation of the audio signal is transferred onto the tape by rearranging magnetised particles of ferric (iron) oxide that are secured to its surface; a particle’s polarisation (which way it is pointing) is a representation of the audio signal that is transferred to the tape via the record head
The playback head ‘reads’ this magnetic signal and converts it back into an electrical signal for amplification
The erase head uses a strong permanent magnet placed near the tape to reset the polarisation of the particles
At low and high levels of magnetisation, the quality of tape is very poor so the signal is recorded with bias
Advantages – cheaper at the time than vinyl; difficult to scratch or damage; easy to copy; longer recording times than LPs; more portable than vinyl records
Disadvantages – sometimes tangle and snap; need to clean recorders to avoid oxide build up; quality degrades with each playing; susceptible to hiss; wow and flutter and print through.

Popular from the late 80s, CDs (compact discs) are optical; they store data as pits which are read by a laser
CDs can hold 74-80 minutes of stereo LPCM audio (16 bit / 44.1kHz as detailed in the Red Book Standard) and have a much wider / more accurate frequency response and less noise than tape and vinyl
The introduction of home CD recorders / drives for computers led to easy sharing of high quality digital copies
Advantages – better signal-to-noise ratio and wider dynamic range; no degradation; cheaper to manufacture than tape and vinyl; quick indexed track access; could use with computers; longer playing time than vinyl
Disadvantages – scratching causes issues and renders parts of disks unplayable; some analogue enthuasists consider the sound of CD as brittle; less portable / easy to share than digital audio files.

Digital and DAW recording uses uncompressed audio during the recording and production stages (e.g. WAV files)
Since the late 90s, compressed digital formats have become more prevalent e.g. MP3 / M4A
These compress audio data very effectively which reduces the file size compared to an uncompressed file (WAV)
Lossy audio compression reduces the file size by losing some frequency content and dynamic detail
Lossless audio compression creates files larger than lossy compression but does not lose any data
Uncompressed audio files include WAV and AIF; lossy compression includes MP3, AAC and WMA; lossless compression includes FLAC and ALAC
The key issues when discussing the quality of digital audio files are the frequencies reproduced and the noise
Lossy compression loses frequency detail and increases noise; how much this occurs depends on the format; lossless compression / uncompressed audio both maintain the original frequency content and level of noise
Advantages: lossless compression reduces file size with the similar quality to uncompressed audio; files are portable and easy to share, meaning it is easy to buy or stream albums
Disadvantages: lossy formats lose some data, reducing quality; there is a lack of physical product; digital data is easy to copy and can affect the viability of the industry and file management must be good to avoid losing data.