26 lines
2.2 KiB
Markdown
26 lines
2.2 KiB
Markdown
# Adjusting Synchronisation on Shairport Sync ("SPS")
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Sometimes, a timing difference can be heard, where the audio coming from the SPS-powered device is slightly ahead or slightly behind another device playing in synchrony. This can sometimes be heard as an irritating "echo".
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This is usually due to audio amplifier delays:
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* If your audio output device (including the amplifier in a TV) includes any digital processing component, it probably delays audio while amplifying it.
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* If your output device is a HDMI-connected device such as a TV or an AV Receiver (AVR), it will almost certainly delay audio by anything up to several hundred milliseconds.
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In these circumstances, if the output from the SPS device is amplified by a conventional analog-only HiFi amplifier – which has almost no delay – it will be early by comparison with audio coming from the other device.
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Conversely, if the output from the SPS device is passed through an AVR, then it could be late by comparison with audio amplified by a conventional audio amplifier.
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The fix for this is to get Shairport Sync to compensate for delays by providing audio to the output device _slightly late_ or _slightly early_, so that when audio emerges from the amplifier, it is in exact synchrony with audio from the other devices.
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The setting to look for is in the `general` section of the Shairport Sync configuration file and is called `audio_backend_latency_offset_in_seconds`. By default it is `0.0` seconds.
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For example, to delay the output from the SPS device by 100 milliseconds (0.1 seconds), set the `audio_backend_latency_offset_in_seconds` to `0.1`, so that audio is provided to your output device 100 milliseconds later than nominal synchronisation time.
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Similarly, to get the output from the SPS device 50 milliseconds (0.05 seconds) early, set the `audio_backend_latency_offset_in_seconds` to `-0.05`, so that audio is provided to your output device 50 milliseconds earlier than nominal synchronisation time.
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Latency adjustments should be small, not more than about ± 250 milliseconds.
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Remember to uncomment the line by removing the initial `//` and then restart Shairport Sync (or reboot the device) for the changed setting to take effect.
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