Adding L and R channels together ???

Using version 1.2.6 I have been transferring old mono lps to audacity to transfer eventually to CD. I have used the stereo option in preferences and it is obvious the two channels are not identical - on any lp sometimes one is slightly stronger and sometimes the other. (may be in future I should use the mono option - I have done a lot of successful click removal using the ‘draw’ tool so I would prefer not to have to re-record using the mono option) Anyway, how do I add each channel to the other to make both channels identical?.

You may find that just using the Normalize effect will do the trick for you.

In Audacity Normalize works on each channel of a stereo pair separately to bring the amplifitude level of each channel to a required level (the default is 0 dB, but I recommend choking it back a little to say -2.0 dB). This is useful if you have and unbalanced recording chain resulting in unbalanced channels i.e. what you have.

In contrast the Ampliy effect will treat a stereo pair as a pair and not treat them independently - but this is not what you need here. For further reading on Normalize v. Amplify see this article in the Wiki:

There are more sophisticated ways in Audacity of taking the tracks apart mixing and rebuilding - but you may find the simpler approach works fine for you, so try that first and then post back if it doesn’t work.

BTW it would also be worth checking the alignment of your cartidge and your arm and check its anti-skate setting is correct - that may be a root cause of the problem.

The really serious restoration and archive audiophiles will often take old mono recordings like this and find the best bits from each channel and patch those together to make the very best track they can from the availabel material - and sometimes from different copies of the same record. I’m not suggesting you do this - it is very long arduous work, usually only undertaken by professionsals.


Thanks, wax cylinder, for getting back so quickly - I will have a good look at the article you suggest. I had tried ‘normalize’ but that sometimes swings one channel markedly stronger than the other. I had wondered about aligment of the cartridge. I have redone one disc using mono and I get the impression that combines the channels. Can you point me in the direction of separating the channels etc

AFAIK there isn’t a tutorial in the Wiki or the manual for this - but I can give you a workflow recipe (and note: I’m sure there are other ways of doing this).

  1. Use Audacity 1.3 x (latest is 1.3.13) not the ancient 1.2 series - get it from here:
  2. Make recording
  3. In the Track Control Panel (TCP) to the left of the track you will see a Little-Downward-Pointing-Black-Triangle (LDPBT) - click on it
  4. From the drop-down menu select “Split Stereo to Mono” - you will now have two independent mono tracks ( the L & R signals)
  5. Make sure you have the clipping indicators turned on - enable “Show Clipping” from the View menu
  6. Select both tracks - CTRL+A is the quickest way to do this
  7. Mix the tracks - use Tracks > Mix and Render
  8. If this introduces clipping (as you have now added both tracks together) you will see this from the red lines - then you will need to Undo the last step and use the Amplify effect to reduce the amplitude of the tracks a bit by using negative amplification - then repeat steps 6&7
  9. Now you will have a single mono track mixed from the two “stereo” channels.
  10. Create a new empty mono track - use Tracks > Add New > Audio Track
  11. Select all the audio in the first (mixed) track - click in its TCP (but take care to avoid the sliders and buttons)
  12. Copy this to the Audacity paste buffer - use CTRL+C
  13. Shift focus to the new (empty) track - click in its TCP (as above take care to avoid the sliders and buttons)
  14. This should have the “Select Start” time at zero
  15. Paste a copy of the mixed track in - use CTRL+V
  16. Go to the LDPBT in the top track and click on it
  17. From the drop-down menu select “Make Stereo Track

And that should do it steps 13/14 are critical as you have to ensure that the two tracks line up exactly. (And hey, I’ve realized that I have just written the draft of a tutorial for the manual or the Wiki - I’ll hold off on that to see if anyone else posts quicker or better workflows for this).

Let us know how you get on with this.


Just noticed this bit - that
That’s very hard manual labour - I know I’ve done it myself in the past with 1.2.

In 1.3 the developers introduced a new effect called Repair whicch will fix up to 128 samples by interpolating from the neighbouring wave forms. See:

That’s still hard work as you still Have to deal with each click individually (I’ve done that too …). In 1.3 there is another new effect aclled Click Removal - it’s ok, but even better is Brian Davies’ excellent ClickRepair package - it costs a little at $40 but produces excellent results and is well worth it if you have a lot of vinyl to process. Brian let’s you have a 21-day free-trial. See this sticky thread:

_You may be interested in reading this workflow tutorial I wrote for the 1.3 manual a while back:


No, you need to stick with the Stereo option. You have a stero cartridge, right? So you are feeding two signals L and R - and unless you have a function in your pre-amp to add these two together to make a momo signal (my old QUAD-33 can do this) - or you want to re-wire your cartridge for mono (not recommended) then you need to stick with the two channels. Just selecting mono input in Audacity will not sum your L&R channels together.


IIRC There is a trick to quickly reduce clicks in this particular dual mono situation, (i.e mono record, stereo pick-up) …

Use Kn0ck0ut to create a track which contains only that which is common to both tracks, i.e. centre pan isolation.

So if there is a click on the one of the dual mono tracks but not on the other it won’t be included,
Kn0ck0ut does add digital artifacts though …

Thanks very much for all your help. Yes, it is a stereo-cartridge. Since my first reply and before I saw this reply I tried using the mono option - I get a slightly different wave form from either channel in the stereo option (which looks like a sum where the channels are markedly different) and the same slightly different waveform if I swap the L & R channels with mono option, so what is it doing if it isn’t summing or averaging?

This free (but slow) plug-in will mono-ize a stereo track … (it works OK with Audacity 1.3)

I don’t think that is always true.
Most USB sound cards will record only the left channel if you select “1 channel (mono)” in Audacity, but I think that some internal sound cards will mix left and right input channels when “mono” is selected.

In the case of recording a mono record with a stereo cartridge, the left and right channels should be pretty similar, but it would be expected that there will be some difference due to the turntable set-up, wear on the record and so on. If you record as stereo, then there are two ways that you can convert the track to mono using Audacity 1.3.13. I would advise using whichever method sounds best.

Method 1:
Click on the track name and from the drop down menu select “Split to Mono”. If one track sounds noticeably better quality than the other, delete the bad track. If they both sound pretty much the same then method 2 will probably be better.

Method 2:
(If you’ve started with method 1, use “Edit menu > Undo” to undo the splitting of the track).
Select the track, then from the main menu bar, “Tracks” menu > Stereo to Mono. This will mix the left and right channel to produce a mono track that is an average of left and right channels.

Ah that’s interesting - as you know I run a USB soundcard and it does just that - hence the oversight.


Thank you Steve. I have now installed 1.3.13 and used your method 2 above. this produces exactly the same waveform as when I re-recorded using the mono option as I mentioned in my second reply to WC. (I am using an internal “Sound Blaster Live! 24-bit” sound card (and Windows XP on a DELL dimension 9100 PC)

A big thank you to all of you who have replied; I really appreciate it.

I am about to start on some 78 rpm transfers. I have a 1946 EMG electric gramophone (real valves!) which has variable speed and uses thorn needles. An electronic wizard friend has extracted the output from the preamp stage (and isolated it safely!)and so I can feed a properly equalised signal of the right strength into the PC sound card. It works great.

In which case have a read of this tutorial from the manual, you may find it useful: