Should our mixes be mono compatible?

Many professional studio engineers maintain that it is essential to ensure a stereo mix is mono compatible. They will be delivering finished masters to a client who will expect the mix to sound good on as many playback systems as possible. But is it also important for us independent music producers working in our home and project studios?

Music is almost always played or broadcast in the stereo 2 channel format. Almost. Most of the playback systems we use output to stereo speakers, headphones or earbuds. The primary systems for listening in stereo include mobile devices with ear-buds, car stereos, TV’s and home theatre systems, laptops, and of course home hi-fi systems. Even multi-channel and surround systems reproduce stereo well.

The Mackie Big Knob has a mono button to help a user check for mix compatibility

So when might our stereo files playback in mono? There are two primary scenarios. Firstly when the device only has a single speaker. The primary devices will be the mono speakers in many mobile phones and tablets. It’s possible that some people might also listen to music through the small system speaker located with a PC tower usually reserved for system sounds. Some tablets have stereo speakers but they are usually located too close to produce a convincing stereo image. Given that many of these devices will never produce anything approaching “hi-fidelity” sound, whatever speaker arrangement they have, and that we cannot optimise our mixes to accommodate them with predictable results, it’s unsurprising that many engineers don’t bother to consider them.

Another device that we might need to consider is the portable FM or DAB radio with it’s mono speaker. These devices are widely used in the workplace and home. But how prevalent are they and should we consider them?

DAB radio

Secondly there will be situations in which stereo sound is encoded to mono during or prior to broadcast and delivered in mono whatever the playback system. For example we may need to consider internet channels, such as YouTube, which may encode our stereo mixes to mono as they are uploaded, or replayed, depending on considerations such as bandwidth. The same may be true for some broadcast radio and TV. The truth is with the proliferation of new internet delivery channels we can never be sure how our mixes may be treated.

Another another important scenario in which mono compatibility might be important is live sound. Because it is often impossible to produce a balanced stereo image for all listeners in a night club or music venue, it is important that playback is mono-centric. This means either narrowing the stereo field at the point of playback or using mixes which do not feature heavily panned tracks that would produce an imbalance. Of course much dance music is already re-purposed for different uses with engineers and producers creating different mixes for different target releases; DJ’s, iTunes, vinyl etc.

Leaving aside the important considerations of music delivery for a moment, exactly what can happen when a stereo mix is summed to mono? The easiest way to find out is to try it for ourselves. If we have a monitor controller it might have a mono button, or we could reset our stereo mix bus to mono, or insert a direction mixer or other plug-in into it.

Logic master fader (left), and summed to mono (right), now missing its stereo inserts!

The primary changes we may hear are ..

1) a change in the level balance between centrally panned sounds such as kicks and lead vocals, and those widely panned stereo and mono sounds
2) changes in ambience and reverberation
3) phase shifts in stereo sounds which may affect their frequency content

The third of these problems primarily arises when a source which has been stereo mic'd contains phase related timing differences between the channels which aren't apparent when heard in stereo.

It should be clear by now that creating the most compatible mixes will involve compromise and we may feel that problematic phase issues aside they are not worth spoiling our carefully considered stereo mixes for. However it is important to check that important sounds such as lead vocals are coherent and bass retains its level and focus. Also, if you make dance music consider creating separate mono mixes for clubs and venues.

On a more positive note, it’s surprising how well many stereo mixes sum to mono naturally, and given that mono produces a very different sound field we can often be quite forgiving of the differences, providing there aren’t obvious problems. This is especially true if you don’t use stereo mic techniques.

Stereo mono compatibility is clearly a complex subject and we have only scratched the surface here, but we hope we have at least given you some food for thought.

Thanks for reading and watching.

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