Series: Spring cleaning for your ears – We'll polish your audio knowledge! Episode 3

Episode 3: Do more channels mean better sound?

More audio channels = better sound quality? A fallacy! More and more speakers ensure better and better sound. Many people share this view - and not without reason. In advertising, it often seems that a 9.1.4 system delivers "fatter" sound than a smaller 5.1 system. In fact, however, the sound quality and the number of audio channels are independent variables! For example, stereo sound can be better than Dolby Digital. How is that possible? If you're looking for an answer, you have to delve into the theory - a little bit, anyway.

2.0, 5.1, 7.1, 9.1.4: What do the numbers stand for?

Sound systems are classified according to the number of audio channels they have - the principle is familiar to most people. A 5.1 system offers channels for five main speakers and a subwoofer. This usually means there are five speakers and a woofer. Strictly speaking, the number of channels does not have to reflect the number of speakers, but that would be another topic.

The key point is: the higher the numbers, the more speakers there are. With 3D surround sound, such as Dolby Atmos, there are also separate speakers for the highs. They are not aimed at the listeners, but at the ceiling. This is intended to provide more dynamics. A corresponding setup could be 9.1.4, in which case there are then four additional speakers for the highs.

Why is more not better?

This brings us back to the core question: Why are eight channels (7.1) not better than six (5.1)? The sound quality is significantly influenced before it is played out! Two key factors are crucial here.

Firstly, the quality of the recording. It sounds trivial, but it's true: if the sound was recorded and processed using inexpensive technology, even the best system cannot extract top-quality sound from the raw material.

Second: the file format. Sound is usually played from a digital source. The best-known example is MP3. This is a compressed data format. Compression means that less storage is required, but also that information is lost.

The same principle also applies to formats such as AC3 (Dolby Digital). It was developed specifically for surround systems and is intended to provide a particularly good sound experience. However, the raw file is also compressed for this - with corresponding losses. The sound is sometimes perceived as "hollow" because it simply does not contain certain components. A counterexample is PCM Stereo. This is an uncompressed, lossless format. This means that all sound information is retained, which leads to significantly better sound quality.

The same principle also applies to Why are there so many audio channels?

5.1, 7.1 and the like were not created to deliver the most exclusive sound quality (although such misinterpretations are rarely corrected). Surround sound was developed for room-filling sound experiences. As the name suggests: the sound surrounds the listeners.

Sound example: In the movie, the dinosaur first screams from the back right, tramples its way ever closer and then builds itself up visibly and audibly in the center of the screen. Here, the audio channels show their full advantages, the entire room is filled with three-dimensional sound. For this to work, however, the soundtrack of the source must support a corresponding system. 9.1.4 (Dolby Atmos), for example, is not available for every film. And even if a film is produced in Dolby Atmos, it is the artistic decision of the producer whether and to what extent the height channels on the ceiling are used.

When is sound quality more important?

Excellent sound quality is important to everyone who values ​​music enjoyment. How rich the sound can be depends on the information density of the source. For example: an audio CD delivers 1411 kbit/s (kilobits per second), while a memory-saving MP3 file only delivers up to 320 kbit/s. AC3 reaches its maximum at 640 kbit/s - but DVDs or streaming usually only offer around 300 kbit/s. This shows that the demands on sound quality are very different. In summary, if you want to hear and enjoy every nuance of a symphony, you need a source with a high bit rate and a speaker that can handle it. If you are looking for room-filling sound with sound from all sides, you are well advised to have (as many) audio channels as possible.

Further information can be found in our video: