Sound Quality (Vinyl)
- 1 Sources of Distortion
- 1.1 Turntable
- 1.2 Tonearm, Cartridge and Stylus
- 1.3 Preamp
- 2 Objective Requirements Of Vinyl Playback
Sources of Distortion
Tonearm, Cartridge and Stylus
Objective Requirements Of Vinyl Playback
These statements are derived from psychoacoustics and electrical constraints that would be necessary to yield objectively optimal playback. These statements also form a concise summary of the audible issues with vinyl.
Pitch, wow and flutter
The playback speed of the turntable must be within 0.3% of 33 1/3 RPM at all times - or 5 cents. Variations of pitch must stay witin the 5-cent requirement and the modulating frequencies must not be audible.
Shockingly, this is extremely hard to achieve in belt-drive turntables for a number of very important reasons. Good direct drives are much better at pitch. (Bad direct drives are much worse at flutter.)
Under certain pathological circumstances, playback tolerances much lower than 0.3% may be audible. For instance, if playing in a very large room with echo on the rear wall, the reflected music will interfere with the speaker output. Beat frequencies could thus develop at potentially [i]any[/i] playback tolerance.
Note that the standard tolerance for center holes (<0.2mm off center) results in a very large wow at inner grooves. (For a 0.2mm deviation, at a groove radius of 60mm the wow will be 0.6% p-p).
The low frequency noise (rumble) of the turntable must not impinge on program material, must not distort amplifier or speaker stages, and must not be audible.
Rumble is an intrinsic part of both the vinyl medium and the turntable. It originates from several sources:
- Low-frequency vibrations from the air and ground are coupled to the cartridge through the turntable and the record itself.
- Low-frequency signals on the record itself. Lateral signals exist due to off-center holes and groove compression at cutting time. Vertical signals exist due to record warping and cutting distortion.
- The resonant frequency of the cartridge-tonearm system, typically 5-15hz, stores and amplifies external energy.
Often times, 5-10dB of the peak amplitude of a vinyl recording is contained in the rumble, and removing it can help increase the loudness for essentially free. Playback with significant rumble can be audible with subwoofers, or can increase distortion by driving speakers closer to excursion.
After RIAA equalization, the system must be able to reproduce frequencies from 20hz to 20khz to within 0.1dB of the source media.
0.1dB is close to the theoretical JND of amplitude for a single sinusoid; tolerances around 1dB in response are usually acceptable.
MM cartridges are well-known for boosting the high end if improperly loaded. Stylus or record wear will eliminate high frequencies. Rumble may make low frequency reproduction difficult.