Applied Acoustics Systems Chromaphone 3 Upgrade Acoustic Object Synthesizer Plug-In (Download) - Manual (Page 71)

Audio and MIDI Settings 71
8 Audio and MIDI Settings
This chapter explains how to select and configure Audio and MIDI devices used by Chromaphone
3 . Audio and MIDI configuration tools are accessed from the Settings view which is accessed by
clicking on the Settings tab in the top of the interface.
Note that in plug-in mode the audio and MIDI inputs, sampling rate, and buffer size are set by
the host sequencer.
8.1 Audio Configuration
8.1.1 Selecting an Audio Device
Audio configuration tools are accessed by clicking on the Audio MIDI Setup button located in the
lower right corner of the Settings view. The Audio Setup dialog first allows you to select an audio
output device from those available on your computer. Multi-channel interfaces will have their
outputs listed as stereo pairs.
On Windows, the audio output list is organized by driver type. The device type is first selected
from the Audio Device Type drop-down list. If you have ASIO drivers available, these should be
selected for optimum performance. The Configure Audio Device button allows you to open the
manufacturer’s setup program for your audio interface when available.
Once the audio input has been selected, you can then select a sampling rate and a buffer size
from those offered by your audio interface.
8.1.2 Latency
The latency is the time delay between the moment you send a control signal to your computer (for
example when you hit a key on your MIDI keyboard) and the moment when you hear the effect.
Roughly, the latency will be equal to the duration of the buffers used by the application and the
sound card to play audio and MIDI. To calculate the total time required to play a buffer, just divide
the number of samples per buffer by the sampling frequency. For example, 256 samples played
at 48 kHz represent a time of 5.3 ms. Doubling the number of samples and keeping the sampling
frequency constant will double this time while changing the sampling frequency to 96 kHz and
keeping the buffer size constant will reduce the latency to 2.7 ms.
It is of course desirable to have as little latency as possible. Chromaphone 3 however requires
a certain amount of time to be able to calculate sound samples in a continuous manner. This time
depends on the power of the computer used, the preset played, the sampling rate, and the number
of voices of polyphony used. Note that it will literally take twice as much CPU power to process
audio at a sampling rate of 96 kHz as it would to process the same data at 48 kHz, simply because
it is necessary to calculate twice as many samples in the same amount of time.