Operation Manual

6.3 Latency Settings 40
6.3 Latency Settings
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 du-
ration 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. Ultra Analog
Session 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 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 you need to calculate twice as many samples in the same amount of time.
Depending on your machine you should choose, for a given sampling fre-
quency, the smallest buffer size that allows you to keep real-time for a reasonable
number of voices of polyphony. To adjust these parameters:
• Launch the Audio Control Panel
• Choose the sampling frequency and the audio format (16, 24, 32 bits)
• Adjust the buffer size
Note that this might not be possible on Mac OS or with ASIO drivers on Win-
dows.
In order to optimize the resources allocated to the calculation of audio by Ultra
Analog Session, it is possible to decrease the ratio of resources devoted to the
calculation of graphics for the interface in favor of audio related calculations. To
adjust this ratio, choose the Preferences command under the Edit menu and adjust
the Performance slider to the desired value between better audio performance
and smoother graphics. This setting may have little noticeable effect on recent
computers.