The Difference Between Sound Formats, Decoders and Upmixers

Sound Format versus Decoder

A sound format and a decoder are two separate things that work together to produce high-quality surround sound in the home theatre.

A sound format is a digital file format that contains an audio signal, such as an MP3, AAC, or WAV file – or in our case Dolby Digital, DTS or PCM audio. These formats determine how the audio signal is compressed, encoded, and stored. Different formats have different levels of quality, compression, and compatibility with different devices.

A decoder, on the other hand, is a piece of hardware or software that can read and interpret the audio signal in a particular format. Decoders decode or decompress the audio signal and convert it into a signal that the rest of the DSP can work with – normally multi-channel PCM audio.

Different decoders are designed to work with different sound formats. For example, a Dolby Digital decoder is designed to decode Dolby Digital-encoded audio signals, while a DTS decoder is designed to decode DTS-encoded audio signals.

In order to play back high-quality audio, the sound format used must be supported by the playback device, and the device must also have a compatible decoder to decode the audio signal. For example, if you have a Blu-ray disc with a Dolby TrueHD soundtrack, your playback device must support sending Dolby TrueHD audio, and your AVR must also have a Dolby TrueHD decoder to decode the audio signal.

In summary, a sound format is a digital file format that contains an audio signal, while a decoder is a hardware or software component that can read and interpret the audio signal in a particular format.

Decoding versus Upmixing

Decoding allows you to hear the audio as it was originally intended, with all the surround sound channels and effects preserved.

Upmixing, on the other hand, refers to the process of creating additional audio channels from an existing audio source. Upmixing is used to create a more immersive audio experience, even if the original audio source was not recorded in surround sound. For example, a stereo audio source can be upmixed to create a surround sound experience by creating additional audio channels and applying sound effects to them. Upmixing can be done using various algorithms, such as Dolby Pro Logic IIx, DTS Neo:6 or the newer Dolby Surround and DTS Neural:X algorithms.

The End to End Signal Path

So in summary:

1. Multi-channel audio is designed on a mixing desk
2. The audio is encoded into a specific format such as Dolby Digital or DTS audio – we will cover the different types of codecs in another article.
3. The playback device will normally send the bitstream compressed audio the the AVR
4. The AVR will use the compatible decoder to decode the number of channels included within the compressed audio stream
5. The AVR can then play back the channels as they are in the source or use an upmixer such as Dolby Surround or DTS Neural:X to expand the number of playback channels to match your speaker configuration