Stereo Lab Listening Room

Click and Pops processing and getting the EQ curves right

A de-clicker for audiophiles

Stereo Lab incorporates an audiophile de-clicker which is optimised for fans of the vinyl disc whose LPs are good condition and for the most part need little or no correction. Importantly, the Stereo Lab algorithm doesn't interpolate or predict the audio. Instead, a robust click-detection algorithm is coupled to an adaptive attenuator which lowers the intensity of clicks rather than attempting to remove them altogether. In this way, audio is never lost or synthesised.

The importance of a robust detection is to ensure there are no false positives and correction is not wrongly applied to musical transients rather than clicks. The Stereo Lab detection algorithm is virtually foolproof. It is biased against detection so, in the event of an ambiguous detection it will rather let a click go through than replace good audio.

Click and noise removal works much better if it is applied before RIAA equalisation because the massive bass-boost of the RIAA equalisation process transforms a very brief dust particle "snick" into a very noticeable "thwack" . So the Stereo Lab de-clicker is incorporated in the phonograph dialogue. When the check box for de-clicking is checked, the process will be automatically invoked as the appropriate disc replay-correction is applied.

De-clicker and Historic Equalisation demonstration

This recording was made in the 1950s on DECCA's then state-of-the-art recording system known as FFRR for Full Frequency Range Recording but before the switchover to RIAA equalisation.

Early Decca LPs of this period used the Decca 33⅓ characteristic (500C-11.5) which is characterised by the time-constants of 1590/318/60µS. If RIAA equalisation is used to reproduce these discs, the bass is over-boosted because of the 100Hz bass-shelf in the 500C-11.5 characteristic. Pspatial Audio's EQ-A2 is a modified version of Quad setting A which is optimised for Decca records and that is the equalisation on demonstration here. The de-clicker is also demonstrated.

The examples below are in two parts. The first part is a recording of an all analogue needle-drop recorded via a very high-quality RIAA pre-amplifier. The second section is the same short musical segment recorded with Groove Sleuth preamplifier and processed via Stereo Lab. In this case, the software was responsible for the DECCA EQ correction and the click removal.

Demo 1 - from the Adagio introduction to movement 1 of Dvorak's Symphony no. 9 in E minor (From the New World)

Things to listen out for:

• Over boosted bass which exaggerates the recorded rumble on this disc. Compare 0:01 - 0:06 with 2:16 - 2:19.
• Also over boosted bass and timpani in bars 9 to 14 (1:05 - 1:30, compare with 3:19 - 3:45).
• Note the woodwinds in bars 6 to 9. There is much better focus to the sound at 2:53 - 3:16 than at 0:39 - 1:00.
• Note also that details such as the cough during the bar 4 horn call (2:47) and the conductor's cue before the ff in bar 9 (3:18). Both are very hard to hear in the analogue needle-drop.

Demo 2 - from the famous Largo

• Once again, note the reduced rumble and surface noise in the Groove Sleuth & Stereo Lab version. The tape edit is even audible at the beginning of the track (1:39). It's quite impossible to hear this in the analogue recording.
• Over boosted bass making the timpani in bar 4 very boomy in the analogue version (0:27).
• Note the better focus to the cor anglais solo in the Stereo Lab version. This is especially apparent when the clarinet joins in bar 11 (2:52).
• But perhaps the most striking difference is the massive click during the A major chord in bar 3. This is absolutely atmosphere-shattering in the analogue recording yet almost unnoticeable in the Stereo Lab processed version.

Demo 3 - Noise levels

A demo for the technically minded this.... The track contains a recording of the residual noise of the LP capture system, before the needle is placed on the record and then after. Once again, the first is with a high-quality analogue set-up: the second via the Groove Sleuth, the PHLUX active cartridge and Stereo Lab. The track is boosted in level by 30dB above normal so as to make the differences easier to hear. Note that:

• With the Groove Sleuth, PHLUX & Stereo Lab, the noise level is very, very low and massively beneath the vinyl record noise-floor.
• And once the needle has been lowered onto the record, the click-reduction algorithms reduce greatly the background noise off the disc itself.

All of which means, when you process needle-drops with Stereo Lab, you're listening to the music, pure and separated from the noise mechanisms which surround replay from records.

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