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wiki:jack_latency_tests [2010/12/12 15:32] – added link to latentor rgareus | wiki:jack_latency_tests [2014/03/18 11:39] (current) – [Interpretation and Analysis] lgarrido | ||
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===== Measuring roundtrip latency with jack_delay ===== | ===== Measuring roundtrip latency with jack_delay ===== | ||
- | [[http://www.kokkinizita.net/ | + | [[http:// |
jack_delay works by emitting some rather annoying tones, capturing them again after a roundtrip through the whole chain and measuring the difference in phase so it can estimate with great accuracy how long has the whole process taken. This is no theoretical estimation, jack_delay is a measuring tool that will give you the real deal. | jack_delay works by emitting some rather annoying tones, capturing them again after a roundtrip through the whole chain and measuring the difference in phase so it can estimate with great accuracy how long has the whole process taken. This is no theoretical estimation, jack_delay is a measuring tool that will give you the real deal. | ||
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* Connecting the output of your audio interface to its input using a patch cable. This can be an analog or a digital loop, depending on the nature of the input/ | * Connecting the output of your audio interface to its input using a patch cable. This can be an analog or a digital loop, depending on the nature of the input/ | ||
- | If you want to measure the latency of a cheap, integrated sound card that only has line-output and mic-input you cannot close the loop with a simple patch cable: both connectors may be mechanically compatible, but electrically they are not designed to work together, so attempting to connect them may harm your audio interface. If you are curious, anyway, you can [[http:// | + | If you want to measure the latency of a cheap, integrated sound card that only has line-output and mic-input you cannot close the loop with a simple patch cable: both connectors may be mechanically compatible, but electrically they are not designed to work together, so attempting to connect them may harm your audio interface. If you are curious, anyway, you can [[http:// |
{{: | {{: | ||
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The [[http:// | The [[http:// | ||
- | Low-latency is not always a feature you want to have. It comes with a couple of drawbacks: the most prominent is increased power-consumption because the CPS needs to process many small chunks of audio-data, it is constantly active and can not enter power-saving mode. Furthermore, | + | Low-latency is not always a feature you want to have. It comes with a couple of drawbacks: the most prominent is increased power-consumption because the CPU needs to process many small chunks of audio-data, it is constantly active and can not enter power-saving mode. Furthermore, |
Stable low-latency (≤10ms) on GNU/Linux can usually only be achieved by running [[https:// | Stable low-latency (≤10ms) on GNU/Linux can usually only be achieved by running [[https:// | ||
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- It seems that for USB devices JACK // | - It seems that for USB devices JACK // | ||
- The latency reported by JACK is inconsistent. | - The latency reported by JACK is inconsistent. | ||
+ | |||
+ | The first issue was explained by ALSA developer Clemens Ladisch in [[http:// | ||
Looking closer at these two issues: | Looking closer at these two issues: | ||
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Alas, total latency measurement can not tell which it is. | Alas, total latency measurement can not tell which it is. | ||
- | |||
===== References ===== | ===== References ===== | ||
- | * [[http://www.kokkinizita.net/ | + | * [[http:// |
* [[http:// | * [[http:// | ||
* [[http:// | * [[http:// |