From CockosWiki

Input Output Issues

Track won't play back

When I play back, my audio track is silent, even though there is activity in the track’s VU meter

The problem is likely to be either with your routing in REAPER, your sound card’s settings or with your audio hardware setup.

REAPER’s Routing:

Make sure that the track’s output is directed to the master.
Make sure that the Master output is directed to the outputs on your sound card to which your speakers or headphones are attached.

Sound Card Settings:

Use the control software supplied with your soundcard to make sure that none of the following has occurred:

Output muted, or volume lowered too much.
Output patched to different hardware output.

Audio Hardware Setup:

Make sure that the amplifier is connected to the same outputs on the soundcard as the output of the Master.
Make sure that everything is connected to the power supply, switched on, and with appropriate volume levels.
Use Windows Device Manager (Control Panel, System, Hardware, Device Manager, Sound Video and Game Controllers) to ensure the device is enabled and functioning correctly.

Tips:

Opening a different audio application and playing any wave file can help you determine whether the problem lies within REAPER or with your Sound Card or Audio Setup.

The problem is also likely to be specifically related to that track or item, especially if you have other projects which do play correctly.

Make sure that the track has not been muted.
Make sure that the item has not been muted (right click over item, Item Properties).
Check the FX Window for the track to make sure there is no FX which is causing the track to be silenced.
Check the track’s volume fader to make sure it is not set too low.

MIDI device can't be opened

I get an error message to the effect that MIDI device(s) cannot be opened

The device may not be connected, or may be in use by another program.

Check that the device is connected and supplied with power.
Check whether another program has use of the MIDI device.
Check that you have not accidentally opened REAPER twice...

Playback pops and clicks

When I play back, I get clicks, pops, stutters or dropouts

First of all, rule out or correct any h/w or device driver issues you have; go to http://www.thesycon.de/dpclat, download and run the DPC Latency Checker there. Work your way through the instructions on that page.

If you're still having problems it probably means that you are attempting to play this project at a latency too low for your system. This is more likely to happen if you use a large number of CPU hungry FX such as Reverb. Try one or more of these remedies:

Consider whether you can rearrange your mix to use fewer CPU intensive plugins, for example by making more use of FX busses to share FX used by more than one track.

If you are using a high sample rate, such as 88200 or 176400, try a lower one. Go to File, Project Settings and reduce the Sample rate to 44100. This will reduce the load on the CPU and you will probably find that you can live with any perceived difference in sound quality.

Consider increasing buffer size. This will increase latency, but should not be a problem when playing back. Go to Options, Preferences, Audio Device. Click on ASIO Configuration to bring up the Control Software for your sound card. Increase buffer size, perhaps to 1280 samples.

Master outputs always clipping and distorting

When I play back, the Master clips into the red and distorts, even though the track level(s) appear quite low

This can arise as a result of routing problems, for example when you have any track or tracks routed to the Master by several different routes at the same time.

Check the Routing Matrix to see if any track or tracks is/are being directly routed to the same audio hardware output as the Master.

If this isn’t the cause of the problem …

Disable all FX to see if this fixes the problem; if it does, reintroduce the FX gradually until you can identify which is causing the problem.

Problems Playing Back MIDI Track

When I try to play an imported MIDI track, it is silent

This can be a routing, sound card or setup issue – see previous entries. In addition it may be caused by a MIDI specific issue. This occurs when the track has not been assigned to a valid MIDI Output device or software synthesizer.

If you are using a MIDI Hardware device, display the tracks' Routing Window and make sure it is assigned to a MIDI Hardware Device.
If you are not using a MIDI Hardware device, display the FX Window for the track, and insert a software synthesizer of your choice (usually DXi or VSTi).

Problems Recording Audio

When I try to record audio, nothing is recorded

The problem here could lie either with your REAPER settings or with your hardware set up.

Make sure the track is armed for recording.
Make sure that the track has been assigned an input.
Check (Options, Preferences, Audio Device) that your range of audio inputs has been defined and enabled.
Make sure under the Options menu that you have the correct required Record Mode set (usually this should be Normal.
Check that Record Input is enabled. Or, if you have selected Record Output, check the FX window for any FX that could be silencing the track’s output.
Make sure that the microphone or lead for the instrument being recorded is connected to the correct audio input.
If the microphone requires phantom power, make sure that the phantom power supply is enabled.
Check your audio input mixer (external hardware desk, sound card mixer software, or both) to make sure that the incoming signal is correctly routed.
Check your audio input mixer (external hardware desk, sound card mixer software, or both) to make sure that the incoming signal is not muted.

Playback Problems

I don’t have enough CPU to play back my project

Almost certainly, this is because you are trying to use more FX than your DAW can handle. Use the Performance Meter to determine which tracks are using the most CPU hungry FX. Then right click over the media items for those tracks and either:

Apply FX to items as new take or
Apply FX to items as new take (Mono).

Then bypass the FX for that track.

The transport flashes red and audio "drops out"

Have a look at Preferences_Audio_Buffering, the section on "Source material buffer size". If the transport flashes red and you hear audio drop out, then raise the "Source material buffer size" setting.

Interface Issues

When I press Space (or some other Transport Control), nothing happens

This happens when focus is with another window, such as the Routing Matrix, or an open Dialog Box. Two possible solutions are:

Give focus to another view such as the Track View or Mixer before pressing the key, or
Use an external MIDI control device such as a BCR2000 and assign transport functions to its various buttons. These will then work regardless of which window has focus, or whether a dialog box is open.

When I try to place the edit cursor exactly where I want it, it moves a little

Snapping may be enabled. If so, use the Options, Enable Snapping command to disable it.

When I try to make a loop selection, the start and end points move from where I want them

Snapping may be enabled. If so, use the Options, Enable Snapping command to disable it.

I add a Volume or Pan envelope to a track, but when I play back the fader does not move

Make sure that Automation Mode is set to Read and the envelope is armed:

I record multiple takes on a track, but only the last one is visible

To view all takes for a track, choose the Options, Show All Takes in Lanes Command, or To view a take other than the last take, right click over the media item and choose the Take command from the context menu.

When I maximize a track, the wrong track is displayed

Check your Vertical Zoom Behaviour settings under Options, Preferences, Editing Behaviour. You probably want to set this to Last Selected Track.

When I zoom in horizontally, the edit cursor disappears from view and I lose my place

Check your Horizontal Zoom Behaviour settings under Options, Preferences, Editing Behaviour. You probably want to set this to Edit Cursor or Play Cursor.

I try to view a window, such as Big Clock or Performance Meter, but I can’t see it on the screen

This can be tricky, and can sometimes happen because of changes made to your Windows display settings. There are two main ways to fix this. Use Windows Notepad to edit the reaper.ini file in the folder C:\Documents and Settings\User Name\Applications Data\REAPER. This should only be attempted if you are confident that you understand what you are doing. For example, if the Big Clock has been lost, delete only that section of the reaper.ini file, save it, close it, then restart REAPER. For example, in the reaper.ini file extract shown here, the Big Clock section is shown as italicized:

[flac encoder defaults]
default_size=12
default=63616C661000000005000000AB
[bigclock]
wnd_vis=1
wnd_left=967
wnd_top=600
wnd_width=426
wnd_height=137
time_mode=0
[namecache]
Analog_In_1_Delta_1010__1_=In 1

A safer option would be to simply rename this file as reaper.old or similar. This will return all preferences and options to their original default settings next time you run REAPER

Undo History

My Undo History window is cluttered with every item and track selection I make

Go to Options, Preferences, General and disable Create Undo points for item/track selection.

Trouble Shooting