Mono and stereo, the difference
Mono and stereo differ in the number of audio channels. With mono, there is a single channel that all speakers output identically. With stereo, there are two separate channels for left and right. This allows voices, music, and noises to come from different directions when listening.
Stereo is the standard for television today, but older movies and series often still run in mono. You can hear the difference primarily when the speakers are far enough apart. On the TV itself, the built-in speakers are usually too close together for this. As a result, stereo tends to sound narrow or thin through them.
The difference between mono and stereo
Mono and stereo are short for monophonic and stereophonic. Mono comes from the Greek word for alone, stereo from a word for solid and spatial. The difference concerns the direction from which a sound comes. Initially, it has nothing to do with sound quality. A mono recording can sound just as clean as a stereo recording.
Mono, one channel for everything
In mono, voices, music, and noises are combined into a single channel. If a TV has two speakers, both receive exactly the same signal. The sound then seems as if it is coming from the center between the speakers.
With mono, a sound cannot come from a specific side. A simple example to illustrate: if a car drives from left to right across the screen in a movie, the engine noise stays in the same place. It can still get louder and quieter. This allows you to still hear whether the car is approaching or moving away, but not which direction it is coming from or which direction it is heading.
Stereo, two channels for left and right
Stereo works with a left and a right channel, each carrying its own signal. Each channel goes to its own speaker. A sound that is only in the left channel clearly comes from the left. If it is equally loud in both channels, you hear it in the center.
However, a sound can also appear at any point in between. During mixing, it is distributed across the two channels so that it appears to be at a specific spot between the speakers. This distribution is called panning.
| Feature | Mono | Stereo |
|---|---|---|
| Audio channels | one | two, left and right |
| Direction of sounds | cannot be mapped, everything from the center | freely distributable between the speakers |
| Speakers for full effect | one is enough | two with some distance |
| Typical on TV | older movies and series | most broadcasts and movies |
Mono and stereo differ in the number of channels and whether a sound can come from a specific direction.
Direction and space in stereo sound
Two speakers can only represent a space between them because the sense of hearing evaluates differences between left and right. The volume and the time at which a sound arrives on each side are particularly important. For this to work, the speakers and the seating position should form roughly an equilateral triangle.
Volume and time between channels
If a sound is slightly louder in the left channel than in the right, you hear it further to the left. The greater the difference, the further it moves to the side. It has a similar effect when one channel outputs the sound slightly earlier than the other. The difference is less than one millisecond. In TV shows and movies, sounds are usually distributed via volume. This has the advantage that the audio can later be mixed down to mono without the sound changing significantly.
Usually, the two speakers are set up so that, viewed from the seating position, they are each offset by about 30 degrees to the left and to the right. They are then roughly as far apart as they are from the sofa.
The voice in the center
On television, voices are almost always at the same volume on both channels. As a result, they appear in the center, exactly where the picture usually is. Music and noises, on the other hand, are often more widely distributed. Noises frequently follow what is happening on the screen, as shown in the car example where the car drives from one side to the other.
However, this center only exists in the mind and is particularly clear when you sit directly in front of the TV. In a seat far to the side, the voice also moves a bit toward the closer speaker. If you permanently sit to the side, you can use the balance control in the audio menu to bring the voice back toward the center. Not every TV and not every soundbar has such a control. On the other seats in front of the TV, however, this shifts the sound to the opposite side.
Mono and stereo in television
TV stations, media libraries, and streaming services today mostly deliver audio in stereo or multi-channel sound. You encounter mono primarily in older productions. Former dual-channel audio often used the two channels for two language versions instead of for left and right. Today, such versions are usually available as separate audio tracks.
Stereo as the standard
News, shows, series, and feature films on TV generally run in stereo. Movies and series are also often available in multi-channel sound, which the TV turns back into two channels for its own speakers. In programs where there is a lot of talking, such as news, a large part of the audio is in the center anyway. The difference to mono is hardly audible there.
Old movies and series in mono
Many older movies and TV productions were recorded and mixed in mono. Even if they are broadcast in stereo, their audio remains mono. Both channels then carry the same signal, so the entire sound comes from the center and noises do not move from one side to the other. This is due to the recording and not the TV.
Some versions were subsequently edited and sound wider. Often, the existing mono sound was just artificially distributed across two channels, for example by making it sound slightly different on the left and right. Real directions are not created this way because they never existed in the recording.
Speakers and playback
How much of the stereo effect reaches the sofa depends primarily on the speakers. With two separate boxes next to the TV, stereo sounds significantly wider than through the built-in speakers or a soundbar. If a device outputs only one channel, it mixes stereo down to mono. Individual sounds can change in the process.
Built-in speakers and soundbar
The speakers of a flat-screen TV are usually located at the bottom edge of the device. Even with a large TV, they are at most one to one and a half meters apart. The couch, on the other hand, is often two to three meters away. From the seating position, stereo therefore sounds rather narrow. Many sounds then seem to come from the center. Some TVs and soundbars widen the sound artificially by processing the audio electronically or radiating part of it against the walls.
With two separate speakers to the left and right of the TV, the stereo effect is significantly stronger. With them, you can choose the distance so that the speakers and sofa form roughly an equilateral triangle.
Mixing stereo down to mono
If a device can only play one channel, it mixes the two stereo channels together. In this process, the left and right channels are added and adjusted in volume. Voices, music, and noises generally remain audible; only the information about left and right is lost.
However, sounds that are slightly offset in time in both channels can change. When mixing down, individual frequencies then partially cancel each other out. This makes the sound seem hollow or thin. Voices in the center are hardly affected by this because they are identical on both sides. This is more noticeable with music and widely mixed noises.
Mono as an audio setting
On some devices and some TVs, the audio can be switched to mono. To do this, you have to look in the settings under accessibility. The mono setting mixes both channels together and outputs the entire sound identically on the left and right. It is intended, among other things, for people who hear less well in one ear. It is also useful if only one speaker is connected. Through headphones, you then also hear music and noises that are actually only on one side with both ears.
Frequently Asked Questions
A mono signal is the same for all speakers, so each one plays exactly the same thing. In stereo, however, the left and right speakers each receive their own signal. Only this allows a noise to come from a specific side or move from left to right with the picture.
Stereo sounds more spatial, especially with music and movies with many sound effects. In talk shows or news, it adds little because there is almost only speaking. Mono has advantages if only one speaker is connected or if you are listening with a single earbud. Then no part of the audio is missing.
For an audible stereo effect, you need two sound sources with some distance between them. Headphones also reproduce stereo because each side receives its own signal. You can even hear the directions particularly clearly through them. A single speaker usually outputs both channels mixed down. Soundbars have several speakers in one housing and can therefore at least somewhat separate left and right.
The TV’s format display is of little help here, because it often shows stereo even for a mono movie if the station occupies both channels. A scene in which someone enters the frame from the side or a vehicle drives by reveals more. If the noise stays in the center, the movie is mixed in mono. You can hear this particularly well through headphones.
A mono movie cannot be converted into true stereo on the TV itself. Some TVs and soundbars have sound modes with names like spatial sound or virtual surround that make a mono sound artificially wider. This makes the sound seem broader. However, noises still do not follow the picture. True stereo is only created when a movie is remixed in the studio and voices, music, and noises are separated from each other for that purpose.