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Audio Out section

The audio drivers are used for both recording and playback. The Audio Out settings affect the outcome when you play sound on the timeline.

Playback buffer samples

for playing audio, small fragments of sound are read from disk and processed sequentially. A larger value here causes more latency when you change mixing parameters but yields more reliable playback. Some sound drivers do not allow changing of the fragment, so latency is unchanged no matter what the value. Since different stages of the rendering pipeline can change the rate of the incoming data, it would be difficult to disconnect the size of the console fragments from the size of the fragments read from disk.

Audio offset (sec)

the ability to tell the exact playback position on Linux sound drivers is poor. The audio offset allows users to adjust the position returned by the sound driver in order to reflect reality. The audio offset does not affect the audio playback or rendering at all. It merely changes the synchronization of video playback. The easiest way to set the audio offset is to create a timeline with one video track and one audio track. Expand the audio track and center the audio pan. The frame rate should be larger than 24fps and the sampling rate should be greater than 32000. The frame size should be small enough for your computer to render it at the full framerate. Highlight a region of the timeline starting at 10 seconds and ending at 20 seconds. Drop a gradient effect on the video track and configure it to be clearly visible. Drop a synthesizer effect on the audio and configure it to be clearly audible. Play the timeline from 0 and watch to see if the gradient effect starts exactly when the audio starts. If it does not, expand the audio track and adjust the nudge. If the audio starts ahead of the video, decrease the nudge value. If the audio starts after the video, increase the nudge value. Once the tracks play back synchronized, copy the nudge value to the audio offset value in preferences. Note: if you change sound drivers or Disable hardware synchronization, you will need to change the audio offset because different sound drivers are unequally inaccurate.

View follows playback

this causes the timeline window to scroll when the playback cursor moves. This can slow down the X Server or cause the timeline window to lock up for long periods of time while drawing the assets.

Disable hardware synchronization

most sound cards and sound drivers do not give reliable information on the number of samples the card has played. You need this information for synchronization when playing back video. This option causes the sound driver to be ignored and a software timer to be used for synchronization.

Audio playback in realtime priority (root only)

for really old computers, this setting allows uninterrupted playback during periods of heavy load. It forces the audio playback to the highest priority in the kernel. Today, it is most useful for achieving very low latency between console tweaks and sound card output. You must be root to get real-time priority. Only experts might want to use this because it interferes with ordinary time-share scheduling and can lock up the system. When this is enabled, audio gets the first shot and burns audio until audio lets go. To explain, there are 2 kinds of scheduling, time-sharing which is the default, and real time where the scheduled task must explicitly request scheduling to allow other tasks to execute. Time-share interrupts when you use up your allocated time slice. Realtime priority audio will execute audio decode until it finishes, which may slow down other types of processing like video decoding. Most decoders use a policy that video may be downsampled to accommodate scheduling, but will never skip audio because it creates a much more obvious defect. This feature helps to make sure audio gets priority over video during decode. Be sure to check apply in order for this feature to take effect.

Map 5.1 →2

playback 5.1 → 2 driver downmix maps 6 tracks to 2 channels when checked, that is mixes 5.1 down to stereo on the output device side. This is different from the patchbay and menubar functions which reset the pan/mix levels of the input channels. In this way, you can render 5.1 media, and use stereo speakers to listen in the same session setup. This downmix only occurs if the playback is 5.1 (6 channels) and the device config is stereo (2 channels).

Gain

set audio gain to a different value than the default of 1.0 This feature, device level gain, corrects for hardware conditions which some devices may need to be useful. For example, you may need to increase the gain for a weak microphone or a noisy speaker, since it affects rendering when you crank up or down the audio via use of the patchbay. With the audio H/W gain support, you have the ability to fine tune the audio volume by some numerical value for the scale. You are adjusting the scaling of data into the audio driver – H/W scaling is done before it goes into or out of the driver. This is a one time linear multiplication of the sample values, and may offer better control than the logarithmic DB gain controls of the application.

Audio driver

there are many sound drivers for Linux. This allows selecting one sound driver and setting parameters specific to it. The currently available possibilities are listed next.

ALSA

is the most common sound driver these days and supports almost all sound cards. ALSA is frequently updated but is very stable.

OSS

was one of the first Linux sound drivers and has an open source implementation with many sound cards supported.

OSS Envy24

is the commercial version of OSS with a variant for 24bit96KHz sound cards. This variant required changes to the way the sound drivers were used and so needed a different driver.

Raw 1394, DV 1394, IEC 61883

are older audio drivers used by camcorders and not much else.

Pulseaudio

Extends the functionality of ALSA. It is a more modern and highly supported driver.

Device

with the down arrow, you can see the device choices on your computer.

Bits

8, 16 or 24 Bit Linear are the current choices for the number of bits of precision CINELERRA-GG should set the device for. The meaning of the number of bits can be misleading. Some sound drivers need to be set to 32 bits to perform 24 bit playback and will not play anything when set to 24 bits. Other sound drivers need to be set to 24 bits for 24 bit playback.

Stop playback locks up

this ALSA only checkbox is needed if stopping playback causes the software to lock up. This has worked some time ago, but may no longer work as expected

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Next: Video Out section Up: Playback A / Playback Previous: Yes, you can watch   Contents   Index

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