Stereo Summing to Mono

Archlabs Linux. I don’t have Audacity installed yet; I’m looking at it as a possible solution to my question. My first post on this forum.

I prefer to listen to recordings in mono with a single, full range speaker. I don’t use vinyl. Much of the music I listen to is only available in two track stereo. When I download a two track recording in a digital file I would like to use the Audacity feature to sum the tracks into one mono track.

My question is: what will that do to the audio quality? Elevated noise? Phasing issues? Something else?

Select the stereo track > Tracks > Mix > Mix Stereo down to Mono.

But. What it does is reduce both original tracks to half-volume and then smashes them together into one mono track. It doesn’t just add them up.

You need that if there is exactly the same thing full volume on both left and right of the original show. If all you did was add those up, you would get 200% overload distortion in your mono track.

I don’t see any reason what you want wouldn’t work.

You can try it given Audacity is free…


You can get some magic distortions. If the original stereo track was recorded with the Left and Right out of phase to get a “deep cave” effect, then the mono mix will be silent. You can fix that in Audacity by splitting up the original stereo track, select one of the two now split tracks and Effect > Invert.

Then recreate the stereo track and mix it down.

That one kills more people than you think because it’s possible to mis-wire a home microphone to record that way by accident. As long as you’re listening in stereo, everything seems sorta normal. The first time somebody listens on their phone, the show dips to nothing. I caught a radio station whose interviewer voice was broadcast that way. I sent them a note.

If your stereo show consists of a full volume, perfect quality track on one side and silence on the other, you’re better off splitting both to mono and delete the silent track. That’s the menus to the left of the track, not the formal tools.

You shouldn’t notice any noise problems. The noise will double when the two tracks get smashed together, but then goes down by half in the mono track creation.

Audacity will add a super tiny shaped-dither noise signal as part of its digital housekeeping. You can make your new files without that, but that’s a poor idea because Audacity converts formats coming in and going out. Dither covers up the minor conversion errors.


Thanks for the detailed response; much appreciated. I will install Audacity and try out what you have suggested. It is quite likely that I will be back with more newbie questions :confused: Thanks again.

Just in case you don’t know this, Audacity edits audio files and it doesn’t work in real-time so you’d have to make mono copies of all your music and it wouldn’t work for TV or streaming, etc.

Another option would be a [u]small mixer[/u].

If you know how to solder you can make a fixed-passive mixer with a pair of resistors. I found [u]this[/u] which uses 4 resistors. I’d use 5-10K resistors for a “more normal” like-level load and all of the grounds should be connected which I don’t see in the picture. And in your setup you’d only be using 3 connections.

…Most commercial music is OK when mixed to mono so it will sound good on mono radio or TV, etc., but amateurs sometimes use effects (or make mistakes) that cause problems.

Thanks. I did plan on making a mono copy and using the copy as a sort of virtual/digital CD, no streaming or live.

I have seen various schematics for a passive resistor network between the signal source and the amp, some with a 1:1 isolation transformer, but intuitively it seems better to me (without any objective data to support this) to accomplish the creation of a mono track in the digital domain rather than squashing two stereo tracks together with hardware. In something like Audacity, as posted above, there is the possibility to avoid increased noise levels, correct any out of phase issues, etc. Also I don’t like the idea of inserting any extra hardware devices in the analogue signal chain.

I’m encouraged to read your comment that for most commercial recordings I should be able to create a decent mono track. The doing it will tell how it turns out :slight_smile:

Can anyone recommend a good converter/ripper for Tidal music only files?

Tidal doesn’t sell music, right? [u]Audacity can record it[/u] but it’s a copyright violation and I’m sure it’s a violation of Tidal’s rules. The artist gets paid a fraction of a cent every time you stream a song.

In something like Audacity, as posted above, there is the possibility to avoid increased noise levels, correct any out of phase issues, etc. Also I don’t like the idea of inserting any extra hardware devices in the analogue signal chain.

Right. Mixing is done by summation (although Audacity will cut the levels in half to prevent clipping, so technically it’s averaging). And… Computers are pretty good at math! :wink:

But, an active analog mixer at line-level is usually better than human hearing so quality isn’t a problem. A passive mixer can be audibly perfect too, but there’s a chance of signal loss. Even transformers can be pretty good but I’d avoid them anyway.

If I was in your shoes I’d get (or build*) a mixer just so the mono setup is compatible with everything.


  • Back in the 70s when quad (4-channel) was a fad I built a subtraction amplifier to “derive” rear channel sound (which is only 3 actual channels). The same circuit is sometimes used as a “vocal remover”, eliminating everything that’s identical and in-phase in both channels. But now, the same vocal removal trick can be done digitally.

I have some familiarity with copyright laws in the US and Canada. You might want to check your analysis.

But thanks for the tip about an line level mixer. I’ll look into it.

This subscription service offers a feature to do real time conversion of stereo to mono, with the ability to adjust gain for each channel separately and also to invert the phase of either channel. Applies to both library source and live streamed.

Edit: I forgot to post the link to the service:

And just a note for those getting excited about the two-resistor mixing arrangement. Any wires or components with sound on them need to be shielded inside a metal enclosure. You don’t just spread the components out on your desk.

Then there’s the actual mixdown. You don’t get a clean half from here and half from over there like the Left and Right digital mix.

Say, for example, Left has to exit the turntable or preamp (through its resistors), make it through its mixdown resistor and then push the circuitry in the mono amplifier. More resistors. It also has to push Right’s resistors backwards. Remember all these circuits are jacked together.

So that’s going to be about an eighth or quarter volume or less from each side. Yes, that’s only about 8dB or 10dB quieter than the expected volume, but we’re doing this as an improvement on the digital system which has no such losses or damage.

You will, of course be shutting your phone down or leaving it on Airplane mode (no Bluetooth, no WiFi) for these operations. Cellphones create all kinds of radiation and interference while they’re working.