Ive got this bookmarked and tried it one one of my wife's recordings..a buddy of mine said that if i copied the one channel to the other, and did a little bit of eqing on one channel, OR adding a VERY small bit of delay on one channel(not enough to cause a phase-y sounding recording)..you can sometimes fake it. I wouldnt do it with something I spread,(im a dumb newbie at this stuff) but for my own listening it sounded better..I think Mr. Kwon posted something about that here as well.
How can I convert my mono recordings into stereo?
Due to either ignorance or just a simple misunderstanding of audio recording and mixdown, I recently found that all of my previous recordings from the last six years are in mono, simply because I failed to pan my tracks. I know how to use panning correctly these days, but how can I convert my mono recordings to stereo using my PC?
Dave (by email)
Editor Paul White replies: As you already clearly appreciate, there is no way to convert a mono recording into a true stereo recording, but there are recognised ways of 'faking it' that work well enough in practice if you're truly unhappy about your work being in mono (and so many great records were, of course). Adding delay to one of the channels is not recommended as the mix may well sound 'phasey' when played back in mono.
A number of plug-ins simulate stereo by boosting some frequencies in one channel while cutting the same frequencies in the other channel by the same amount. If you have access to one of these, that's great, but if not, you can do the same thing with a graphic equaliser (hardware or plug-in) by setting alternate bands to cut and boost on the left channel, then making the right channel a mirror image of this. I find that it's best not to process frequencies below around 120Hz when doing this, so leave all the bands below 120Hz or so in their flat position.
A refinement of this technique is, instead of setting the frequency bands randomly or alternately, is to try to pick out the key frequencies of specific instruments (some in the left channel and some in the right). Again, both channels must be mirror images of each other, otherwise the tonal balance will change and your mono compatibility will be lost. The result of this processing is a significant sense of stereo spread, though the positioning of individual instruments remains quite vague.
Another option, which can be combined with the above or used on its own, is to process the entire mono mix using a short stereo room ambience reverb setting comprising early reflections with little or no following reverb. This adds a sense of the performance taking place in a real three-dimensional space, but take care to add only enough to create the right illusion -- you don't want your mix swimming in extra reverb. If you plan to denoise your mix, do this before adding the reverb, as this will help put back some of the low-level information that budget denoisers often take away.
Technical Editor Hugh Robjohns adds: If your source material is something fairly simple and inherently 'narrow' or mono anyway, like a single vocal over a single acoustic guitar part, for example, adding a little stereo reverb with some nice early reflections is all that's required to produce a perfectly valid stereo track.
With more complex material, the classic way to fake stereo is by using comb filtering. The detail of the way to do this is will depend on your own equipment and I note that you want to achieve this with a computer. However, the basic plan is as follows.
First, arrange for the original mixed mono track to feed both left and right stereo outputs. Next, derive a post-fade feed from the original track and pass it through a high-pass filter (possible in another channel strip) set to turn over at about 100Hz -- but feel free to experiment. The idea of the filter is to ensure that low frequencies remain in the centre of the stereo image, since otherwise they'll tend to move over to the left-hand side.
Now, take the output from the filter and pass it into a delay line set to about 7ms, and again, you can experiment with the delay setting. Don't go too short, but anything from about 4ms up to 70 or 80ms will work well -- the bigger the value, the bigger the 'room' will sound, especially at the top end of the range.
Split the output from the delay into two and mix it back into the stereo output along with the original mono track. Pan one delay output fully left and the other fully right, but with a phase inversion. It's vital that the split delay cancels out in mono, which means that there must be exactly equal and opposite amounts of the delay in left and right. You can check this by muting the original mono track, and it should all go very quiet.
If you adjust the level of the delay output, you can control the apparent stereo width from mono with no delay output at all, through to very wide as you match levels of original mono source and delayed output. However, don't go mad -- try to keep the stereo effect reasonably subtle.
The advantage of this technique is that while it sounds complex to achieve, it's completely mono-friendly, meaning that it will work perfectly when broadcast over mono radios and the like.
Topic: Repairing Channel Loss (Read 1972 times)