$Page Driver Error Compensation 
$TargetName Driver Error Compensation

In this lesson, we'll configure Live to compensate for latencies when recording audio from external sources. The term *latency* refers to the unavoidable delay that all audio signals experience on their way to and from the computer.

-> If you haven't already tuned Live's audio I/O by completing the $Link Setting up Audio I/O <Lesson:Builtin/3-Hardware Setup Category/1-Setting up Audio IO> lesson, you'll need to do that *before* beginning this lesson.

-> You'll also need an *audio cable* which can connect one output of your audio interface to one of its inputs. It doesn't matter if this is an analog or digital connection, but it must be a real *hardware* connection.

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*This lesson is accompanied by a Live Set which you'll be interacting with as you follow the lesson. Whenever you're ready, please click $Link here <Set:/Sets/Driver Error Compensation.als> to load the Live Set.*
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Driver error compensation is only relevant in a *direct monitoring* scenario, that is, when the musicians being recorded do not hear their own signals through the computer.

It shouldn't be confused with *plug-in delay compensation (PDC).* Driver error compensation addresses delays incurred by the audio interface and its drivers. PDC deals with delays caused by devices and plug-ins that need to look forward in time (dynamics tools or convolution reverbs, for example), and is explained in "Device Delay Compensation" section in the manual's "Working with Instruments and Effects" chapter.

Please click the *Next Page* button below to proceed.

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$Page Preparations 
$TargetName Preparations

This Live Set contains two tracks. The first track, *1 Audio,* contains a single drum sound which begins right at the start of the Set. The next track, *2 Audio,* is empty. We're going to use this track to re-record Live's output through an external connection:
AdjustingLatencyLiveSet.png

Please make sure that the *Follow* switch in the Control Bar is turned off; we don't need the display to scroll:
FollowOff.png

Please connect an audio cable from your audio interface's output 1 directly to the interface's input 1. It doesn't matter whether this is an analog or a digital connection; it is important, however, that you make a real hardware connection.

Press the computer's *space bar* to play the Arrangement. The level meter of *1 Audio* will light momentarily as the drum sound from the beginning of the Arrangement is played. Press the space bar again to stop playback.

Replay the Arrangement with the space bar and watch the level meter of *2 Audio:* If the external connection is working, you should see a signal here as well (even though the meter appears grey). If the signal is too strong or weak, you can adjust the *Master Volume* (in the Master track) and try again until the signal is about equal to *1 Audio.*
TrackTwoMeterAndMasterVolume.png

Remember to press the space bar again to stop playback when you're done.

There's one more preparation to make before we can record: make sure that the "Create Fades on Clip Edges" switch is turned *off* in the $Link Record/Warp/Launch Preferences <Pref:RecordWarpLaunch>:
FadePref.png

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$Page Re-Recording 
$TargetName Re-Recording

Now we're ready to record the output of *1 Audio* into *2 Audio.*

Click the Control Bar's *Arrangement Record* button:
RecordButton.png

If the "Start Playback with Record" preference is enabled in the Record/Warp/Launch tab of Live's Preferences, recording will start immediately. Otherwise, start the recording manually by pressing the space bar and end a moment later by pressing the space bar a second time. The recording will produce a new clip in *2 Audio:*
NewClipInTrackTwo.png

Double-click the title bar of the new clip to display its contents in *Clip View.* In the *Sample Display,* you should recognize the drum that we just recorded from *1 Audio:*
NewClipInClipView.png

Please turn off the *Warp* switch for the new clip. This allows us to adjust its timing in milliseconds instead of beat-time.
WarpSwitchOff.png

If you look closely at the clip's waveform - zooming in if necessary - you might see that the drum sound starts somewhat later than the beginning of the sample (If not, all the better for you, as there's nothing left to do! But we suggest that you continue with the lesson just to be on the safe side.):
KickHitLate.png

Ideally, there should be no delay here, since we started recording at the Arrangement's beginning, right where the drum hit in *1 Audio* is located. In the real world, however, there's always some amount of delay incurred when going in and out of the computer.

(If you weren't able to perfectly match the level of the original audio when recording it back in, you might want to adjust the new clip's *Clip Gain* so that the waveform is easier to see.)
ClipGain.png

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$Page Adjusting Values 
$TargetName Adjusting Values

We're going to offset the clip's *start marker* so that the clip starts at exactly the same point as its contents. Please click in the rightmost *Start* field (which currently represents milliseconds), then press the *up* arrow key repeatedly to increase its value in increments of one millisecond:
StartMarkerField.png

As you do this, the clip's start marker moves right, and the waveform seen in *2 Audio* scrolls left. At some point, the waveform of the original drum sample in *1 Audio* and the waveform of the recorded copy in *2 Audio* will align:
BothClipsAlign.png

If you can't get the waveforms to align perfectly, you can adjust to the sub-millisecond level by holding $CommandMod and dragging the *start marker:*
Submillisecond.png

Once the waveforms are aligned, take note of the value in the Start field. (If you've adjusted the start marker to the sub-millisecond level, please note that this will *not* be shown in the clip's Start field - you'll need to approximate any offset that's between whole milliseconds.) Then $Link open Live's Audio Preferences <Pref:audio>.

Now enter the value that you noted into the *Driver Error Compensation* field, approximating any sub-millisecond offset if necessary:
ErrorCompensation.png

We've now determined how many milliseconds the audio interface's driver is behind by, and have informed Live so that it can compensate for the latency in our recordings from now on.

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$Page Verifying the Overall Latency 
$TargetName Verifying the Overall Latency

Let's verify our work. Select the clip in *2 Audio* by clicking on its title bar, then press the *Delete* key to remove the clip.

Let's record another pass: enable the Arrangement Record button once again (and press the space bar if necessary to manually start recording.) Stop the recording after a few moments. And there you have it, the waveform of the new clip aligns with the original, without any manual adjustment:
TheProof.png

From now on, Live will take care of latencies, and you won't have to bother with this again unless you change your audio hardware. What follows next is some theory which you're most welcome to skip!

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$Page Latency - Some Theory 
$TargetName Latency - Some Theory

*What does the Driver Error Compensation setting achieve, and why is it needed?*

Imagine that you're recording a drummer into Live. The drummer plays along to Live's metronome or music from the Live Set. Monitoring is turned off on the tracks you are recording. The signal that Live receives from the drummer is late with respect to Live's own time base due to the latency incurred by the audio hardware: the time it takes the metronome or music signal from Live to reach the speakers (and thus the drummer's ears) plus the time it takes the drum signals from the microphones to reach Live.

Live compensates for these latencies by moving the recorded samples ahead in song time. To do this, it needs to have precise information about the actual input and output latencies in the system. The latency value reported to the software by the audio hardware drivers is not always completely accurate, however. The Driver Error Compensation setting is a way to tell Live about any deviations from the reported values.


*Why does this only matter when monitoring is off?*

Suppose monitoring is on, and the drummer is wearing closed headphones through which he can now hear both Live's metronome and his own playing. The same latencies still apply, and the drummer is, in fact, hearing the result of his playing late. If latencies are low enough (a few milliseconds), then the drummer will compensate for the latencies by hitting the drums a bit earlier, and the recorded samples will be in time with Live's time base.

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