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## Converting controls to signals

Example C03.zipper.noise.pd (Figure 3.13, part b) demonstrates the effect of converting a slowly-updated control stream to an audio signal. This introduces a new object:

: a ramp generator with control output. Like `line~`, `line` takes pairs of numbers as (target, time) pairs and ramps to the target in the given amount of time; however, unlike `line~`, the output is a numeric control stream, appearing, by default, at 20 msec time intervals.

In the example you can compare the sound of the rising and falling amplitude controlled by the `line` output with one controlled by the audio signal generated by `line~`.

The output of `line` is converted to an audio signal at the input of the `*~` object. The conversion is implied here by connecting a numeric control stream into a signal inlet. In Pd, implicit conversions from numeric control streams to audio streams is done in the fast-as-possible mode shown in Figure 3.4 (part a). The `line` output becomes a staircase signal with 50 steps per second. The result is commonly called "zipper noise".

Whereas the limitations of the `line` object for generating audio signals were clearly audible even over such long time periods as 300 msec, the signal variant, `line~`, does not yield audible problems until the time periods involved become much shorter. Example C04.control.to.signal.pd (Figure 3.13, part c) demonstrates the effect of using `line~` to generate a 250 Hertz triangle wave. Here the effects shown in Figure 3.5 come into play. Since `line~` always aligns line segments to block boundaries, the exact durations of line segments vary, and in this example the variation (on the order of a millisecond) is a significant fraction of their length.

A more precise object (and a more expensive one, in terms of computation time) is provided for these situations:

: exact line segment generator. This third member of the "line" family outputs an audio signal (like `line~`), but aligns the endpoints of the signal to the desired time points, accurate to a fraction of a sample. (The accuracy is limited only by the floating-point numerical format used by Pd.) Further, many line segments may be specified withing a single audio block; `vline~` can generate waveforms at periods down to two samples (beyond which you will just get foldover instead).

The `vline~` object can also be used for converting numeric control streams to audio streams in the nearest-sample and two-point-interpolation modes as shown in Figure 3.4 (parts b and c). To get nearest-sample conversion, simply give `vline~` a ramp time of zero. For linear interpolation, give it a ramp time of one sample (0.0227 msec if the sample rate is 44100 Hertz).

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