APPLIED ACOUSTICS SYSTEMS ULTRA ANALOG Instrukcja Użytkownika Pobierz pdf (Strona 57)

Audio and MIDI Settings 57

6 Audio and MIDI Settings

This chapter explains how to select and conﬁgure Audio and MIDI devices used by Ultra Analog

VA. Audio and MIDI conﬁguration tools are accessed by clicking on the Audio Setup button located

in the lower left corner of the Ultra Analog VA interface and the MIDI button located just below

the MIDI led in upper part 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.

6.1 Audio Conﬁguration

6.1.1 Selecting an Audio Device

Audio conﬁguration tools are available by clicking on the Audio Setup button located in the lower

left corner of the Ultra Analog VA interface. 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.

6.1.2 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 is 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 doubles this time while changing the sampling frequency to 96 kHz

and keeping the buffer size constant reduces the latency to 2.7 ms.

It is of course desirable to have as little latency as possible. Ultra Analog VA 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 your computer, the preset played, the sampling rate, and the number of

voices of polyphony used. Note that it literally takes 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 you

need to calculate twice as many samples in the same amount of time.

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