REAPER tips and frequently-asked-questions

Question: I have a stereo file (2 channels) but I only want the left (or right channel) of it (possibly because the other channel is empty/silent). How can I isolate this channel?

Import the stereo file into your REAPER project. Select the audio region representing the file, and then choose Item: Item Processing: Explode Multichannel Audio... from the menus. You will get a series of child tracks for the left, right, etc channels of the original file. You can delete the child tracks you don't want and drag the one(s) you do want out of its parent track to an independent position in the project's list of tracks. If you are doing this not as a part of a project but simple as an operation on an audio file, you could now use the Render dialog (File: Render) to create a new, independent mono (1 channel) file.

Question: When I reset the main output metres and play my project, I see one reading for the peak (highest) sample level - but when I render my project to a new, independent audio file it has a different peak sample level! What is going on?

The most likely cause of this discrepancy is a change in the sample rate or number of channels (mono vs stereo, etc). Assuming you have explicitly set the sample rate of your project (in Project Settings) when you playback the project everything that is sent out to the DAC is calculated based on that sample rate. If you have a different sample rate in your Render settings, the audio will be calculated on the basis of your project sample rate and then passed through SRC (sample rate conversion) before being written to the new file. Unless there is a good reason for the rendered file to be at a different sample rate than your project rate (for example: making an audio CD from a 48 or 96 kHZ source project), there's a good chance you've made some kind of mistake with sample rates. Do you really need to render at a new sample rate? In the event that you do, simply adjust your master gain settings based on what you observe in the rendered file rather than what you see in the metres. PS: when you render make sure that the resampling mode is "Extreme, 512 points" for the least degradation due to SRC (sample rate conversion).

Question: I have rendered a multi-channel mix-down as a single interleaved file, and I would like to check that every channel contains what it is supposed to - but I am no longer in the studio with a multi-channel speaker array. What should I do?

Import your multi-channel interleaved file into a new, blank REAPER project. Add an instance of the JS: IX/Mixer_8xM-1XS FX plugin to the track on which you imported your file. The 8 sliders labeled Level 1-8 will let you choose which channel to listen to, and the 8 panning sliders below that will let you pan a given channel's signal to the left or right. You can use this plugin to isolate each individual channel from your multichannel mix, listen to it on headphones (or a simple stereo speaker setup) and verify that everything is there which needs to be there.

Proposed Additional Questions - Place your suggestions for future REAPER tips here!:

Question: I can't hear certain audio files once I render my 8-channel and play it back, what's going on!?
Hello everyone, Tanya here! A lot of people have been running into the exact same issue I had a few days ago. If you notice that some of your sounds are not playing once you exported your 5.1, 7-channel, or 8-channel - keep reading! Check out your project sample rate: if you're set to 48000Hz and you notice these blue 'i' icons above some of your imported wave files - then you have a sample rate change. Go to your project settings and in the 'playback re-sample mode' and the 'render resample mode' check off "Extreme, 512 points." Also when you render your project make sure that the settings are set to Extreme (512pt HQ Sinc - NON-REALTIME), and of course make sure you have the correct channel number for rendering. Make sure to play-back your exported .wav file in Reaper by importing it and setting the correct channel definitions - this is just to double check if everything is there, in the right place, and playing correctly.

Question: Why do my files suddenly fall silent at a certain point while playing back on REAPER?
This problem is an interesting one. What happened to me was that anytime I wanted to playback my stereo composition everything would fall silent at a specific point. I noticed that if I played my piece from this silent point, that the project file would continue to play again (as if nothing were wrong at all), but if I played the entire project from the beginning that silent point would cause everything to mute. The easiest way I solved this problem was by deleting the file that I suspected to be causing the problems, and replacing it completely. This seemed to solve the issue, which led me to believe there must have been some sort of file corruption issue that REAPER did not notify me of.