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faq:start [2011/06/07 16:13] – howto specify a device by name emrum | faq:start [2015/11/16 11:02] – [Q: What about timers and timing ?] 202.77.55.169 | ||
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====== Linux Audio User FAQ (Frequently Asked Questions) ====== | ====== Linux Audio User FAQ (Frequently Asked Questions) ====== | ||
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===== General ===== | ===== General ===== | ||
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[[wiki: | [[wiki: | ||
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+ | In linux kernels 3.0 and later, many of the additionally required realtime patches have been incorporated as standard. For those who are recording Audio, a standard non-realtime kernel may be sufficient for your needs, and running Jack with a non realtime kernel will work fine. | ||
+ | |||
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+ | For those who write a lot of Midi, the standard kernel timing is set at 250Hz, and realtime kernels are generally set at 1000Hz. You may still have to use a realtime kernel to obtain accurate midi playback using the higher timing setting. | ||
==== Q: Some of my applications sound a (half)tone too high/low, have a wrong pitch ? ==== | ==== Q: Some of my applications sound a (half)tone too high/low, have a wrong pitch ? ==== | ||
**A:** It's likely, that the sample-rate of the programs you're using doesn' | **A:** It's likely, that the sample-rate of the programs you're using doesn' | ||
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* [[http:// | * [[http:// | ||
* [[http:// | * [[http:// | ||
+ | * [[http:// | ||
**Applications** | **Applications** | ||
* [[http:// | * [[http:// | ||
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==== Q: What about timers and timing ? ==== | ==== Q: What about timers and timing ? ==== | ||
- | Modern PCs provide good hardware timing sources. | + | For moderate to new hardware, TSC is the best hardware timing sources. |
- | One of it is the RTC (real-time-clock). Another one is the HPET (high-precision-event-timer), which is preferable | + | |
Then there is a software layer (in the kernel) to make available the hw-timers to the applications, | Then there is a software layer (in the kernel) to make available the hw-timers to the applications, | ||
One example is the usual system-timer. | One example is the usual system-timer. | ||
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(see: priority settings, rtirq). | (see: priority settings, rtirq). | ||
- | **How to know, if a HPET (hardware) is available? | + | **How to know, if a TSC / HPET (hardware) is available? |
+ | dmesg | grep -i tsc | ||
dmesg | grep -i hpet | dmesg | grep -i hpet | ||
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cat / | cat / | ||
- | **Related Kernel Options | + | **How to config kernel for HPET?** |
< | < | ||
# cat .config | grep -i hpet | # cat .config | grep -i hpet | ||
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Related Articles: | Related Articles: | ||
[[http:// | [[http:// | ||
+ | [[http:// | ||
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options snd-usb-audio index=2,3 pid=0x4567, | options snd-usb-audio index=2,3 pid=0x4567, | ||
+ | |||
+ | [[http:// | ||
[[http:// | [[http:// | ||
+ | |||
+ | . | ||
==== Q: Is it possible to use a label (device name) instead of a number, when referencing a soundcard (e.g. in qjackctl) | ==== Q: Is it possible to use a label (device name) instead of a number, when referencing a soundcard (e.g. in qjackctl) | ||
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- | ==== Q: How to setup the JACK audio server? (jackd) ==== | + | ==== Q: How to set up the JACK audio server? (jackd) ==== |
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==== Q: What is an xrun? ==== | ==== Q: What is an xrun? ==== | ||
- | **A:** A buffer-underflow (a buffer (a count of bytes or samples) | + | **A:** A buffer is not filled in time for the requesting software to use it. Sound data does not arrive fast enough so that the requesting software |
- | // | + | An obvious fix for this is increasing |
- | . | ||
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- | . | ||
===== MIDI ===== | ===== MIDI ===== | ||
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is what you see in the ' | is what you see in the ' | ||
- | **Currently the two midi routing | + | **Currently the two MIDI routing |
leads to some confusion.** | leads to some confusion.** | ||
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(on debian/ | (on debian/ | ||
- | Due to a missing audio standard for USB 2.0, support | + | Support |
. | . | ||
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+ | {{tag> |