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How-to: Calibrate Scratch Live

Why is it important to calibrate Scratch Live?

In the standard configuration of Scratch Live an analogue audio source (turnable / CDJ) sends the Scratch Live control signal into a Rane Scratch Live hardware device, where it is digitized, sent to the Scratch Live software and used to control playback of a digital audio file. It is important to calibrate your set up so the software can distinguish between what is heard as the control signal and what is recognized as background noise and ignored. 

If you have not correctly calibrated Scratch Live for your system and environment you may run into a number of playback issues including glitchy/skipping playback and your tracks not playing at all.

How Scratch Live tracks the control vinyl

There are two parts to the Scratch Live control signal: The directional tone, and the noise map. These two parts of the control signal perform two different functions in controlling Scratch Live:

- The directional tone provides the current speed and direction of the record

- The noise map tells the software precisely where on the record the needle is currently.

The noise threshold

The noise threshold in Scratch Live is the limit below which the input signal will not be interpreted as a control signal. In other words, if it's below the threshold, it is considered noise and ignored by the software. This setting is necessary because a turntable stylus is very sensitive and will inevitably pick up noise from the environment as well as the signal on the record. This especially noticeable in the noisy environment of a live show or busy club.

Noise threshold slider
Noise threshold slider

The scopes

The scope views on the setup screen in Scratch Live display the input signal as a phase diagram. The key factors to look at on the scope display are crisp clean lines, round shape, and the tracking percentage in the lower right corner. This view shows how well Scratch Live is tracking the control signal.

Scope view
Scope view

Setting the noise threshold

1) Turn the sound system up the level you will be playing at during your performance. 

2) Play a track from an audio CD or from the other deck in internal mode.

3) Place the needle on the record but keep the turntable stopped.

4) Click and hold down the Estimate button for a few seconds - Scratch Live will estimate the optimal threshold setting for the current environment. Alternatively you can try manually moving the estimate slider to the right until you notice the number in the upper-right corner of the scope view stops fluctuating.

You should be at the best point for good tracking of the vinyl movement and ignoring noise.

5) Repeat this process for each deck. 

NOTE: The process for calibrating a cd player is almost the same. The only difference is you'll need to press pause on the cd deck with the control cd in the player before hitting the estimate button.

Adjusting the scopes

Once you have set the threshold, start both turntables. For optimal performance the inner ring should be as close to circular as possible. Use the scope zoom slider (1x to 16x) to zoom in or out as necessary. Use the scope L/R balance and P/A balance controls to adjust the shape of the inner ring. The number in the top left corner of the scope view gives the current absolute position within the control record or CD. The number in the top right corner is the current speed in RPM.

Adjusting the scope views

Adjusting the scope views

In the bottom left is the current threshold setting, and the number in the bottom right shows the percentage of readable signal – this number should be at least 85% when your system is calibrated properly.

If you are unable to get a good tracking percentage and your scope views look irregular you can take a look at our article on Diagnosing the Scope Views.