View source for Talk:Tutorial - Overdubbing using your computer's on-board sound card

=Archiving Koz' latency section on the Talk page=
Removed in favor of the [[Latency Test]] page.
{{ednote|'''Peter 18Jul16:''' [[ToDo-2]] images need updating as we now have the pinned play/record head button at the left in the Timeline. }}

==Setting the Recording Latency==
<div class="note">
*To achieve lower latency software playthrough on Windows you can:
** (Only gives somewhat lower latency): On Windows Vista and 7, right-click over the <span class="menu">Speaker icon</span> by the clock, choose <span class="menu">Recording Devices</span>, right-click over the input, choose <span class="menu">Properties</span> then on the "Listen" tab, enable "Listen to this device". 
** (Advanced) Compile Audacity with [http://wiki.audacityteam.org/wiki/ASIO_Audio_Interface ASIO®] true low latency support. Ask on the [http://forum.audacityteam.org/viewforum.php?f=19 Compiling Audacity] board of the [http://forum.audacityteam.org/ Forum] if you need help.  
</div>

Click "'''Home'''" then click "'''Record'''" and you will get a new recording underneath the first one. Sing or perform in time to the first track; when finished click on "'''Stop'''" then "'''Home'''".

The show will have two tracks, one from each performance, but it may be seriously out of time or rhythm -- even though you were in perfect time when you recorded it. This is '''''[[Glossary#latency|recording latency]]''''' and you can adjust it to zero using Audacity's latency tools; done properly, both the live recording session and the later playback will be in perfect time.

*Choose <span class="menu">File > Close</span> click "'''Don't Save'''".

*Choose <span class="menu">File > New</span>.

*Choose <span class="menu">Generate > Click Track</span> click "'''OK'''".

*Audacity <span class="menu">Preferences > Recording</span> set "'''Latency Correction'''" to [ 0 ] milliseconds, click  "'''OK'''".

*Play the new track and set Audacity's volume to loud but not painful.

*Take off your earphones; place one of the headphones or earbuds against the built-in microphone.
:[[File:EarbudMacBookProMic.JPG]]

*Click "'''Record'''".  Track one's click track is now being recorded -- badly -- on track two through the headphone and microphone -- good fidelity here is irrelevant.

*Do this for five or ten seconds and click "'''Stop'''".

*Select the new track and choose <span class="menu">Effect > Amplify...</span>  (accepting the defaults) click "'''OK'''".

*Put your headphones back on.

*Click "'''Play'''", both tracks will probably play out of step.

*Magnify the [[Timeline]] around one of the pair of clicks ''(drag-select and <span class="key">CTRL+E</span> or <span class="key">CMD+E</span>)''.

*Drag-Select the distance between the start of the click on the top track and the start of the same click on the bottom track.<br>
:[[image:LatencyMonoMac.png‎|Audacity Project with latency - Mac OS X screen shot]]
:That's how much the rhythm misses and that's the latency. Keep magnifying until you can get a good shot at accuracy. <span class="key">CTRL+3</span> or <span class="key">CMD+3</span> to back out slightly if you magnify too much by accident.

*At the bottom of the Audacity window in the Selection Toolbar set the middle time control to "'''Length'''" (one of the two radio buttons) then change the format using the dropdown menu to:
::hh:mm:ss: + milliseconds<br>
:You're mostly interested in the milliseconds -- the last numbers on the right. The reading in the example above is 209msec.

*Audacity <span class="menu">Preferences > Recording...</span> set Latency Correction to [-209] milliseconds then click "'''OK'''".

*Close the bottom track ([X] to delete in the top left corner of the track); put the headphone over the microphone grill again and click "'''Record'''".
:This time the two click tracks should look perfectly aligned (or very close to it) and sound perfectly in time. If not, zoom in, measure the new difference and add that number to the latency value.<br>
:[[image:NoLatencyMonoMac.png‎|Audacity Project with no latency - Mac OS X screen shot]]
:In this example, the tracks align to within 23 ''samples'', which is about 0.5 milliseconds - less than the smallest correction you can make in the Latency Correction. This is as good as it gets.

<div class="note">Before you get too obsessive about this, an orchestral musician once told me that the chances of any two instruments in the orchestra starting the same note at the same time is zero, so you don't need to adjust things down to the digital sample level. The latency values on home computers can wander in normal use.</div>