Calibration principles

Scratch LIVE system overview

In the standard configuration of Scratch LIVE an analogue audio source sends the SSL control signal into a Scratch LIVE interface, where it is digitized, sent to the SSL software, and there used to control playback of a digital audio file, which is sent back out to the SSL hardware and converted back into an analogue audio signal.

Why is calibration important?

Since Scratch LIVE is controlled by an analogue signal, there is no guarantee of what state that signal will be in by the time the software gets to interpret it. Therefore, SSL needs to be able to handle a wide range of signals, and be configurable to use them optimally. Calibrating is just configuring your software to your system.

How Scratch LIVE tracks the control vinyl

There are two parts to the Scratch LIVE control signal: The directional tone, and the noise map.

Listening to the control vinyl, the directional tone is the 1 kHz tone. The noise map sounds like random noise over the top of the tone.

What the two parts do is provide two different functions for controlling Scratch LIVE. The directional tone provides the current speed and direction of the record, while the noise map tells the software precisely where on the record the needle is currently.

The noise threshold

A threshold is a lower limit, below which a process will not occur.

In the case of Scratch LIVE, the noise threshold is the limit below which the input signal will not be interpreted as control signal; in other words if it's below the threshold, it is considered noise and ignored.

This setting is necessary because a stylus is very sensitive, and will inevitably pick up noise from the environment as well as the signal on the record, especially in the noisy environment of a live show.

The scopes

The scopes 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.