Understanding digital audio – an A-Z guide
Confused by some of the language used to describe audio equipment? We’ve created a quick guide to help you out.
The basics: how digital audio is recorded
Because real-world sound varies continuously, digital recording is always an approximation of the full range of sound in the world. However, advances in recording technology are constantly expanding the range and accuracy of what can be recorded digitally.
When a digital recording is made from an analogue source – such as a live concert or musicians in a recording studio – the sound is sampled at regular intervals. The amplitude of the sound is recorded as a number, creating a digital record of the analogue audio source as a series of discrete numbers.
How much of the original analogue sound is captured by the digital recording depends mainly on the sampling rate and the bit depth (how many samples are taken in a second, and how much information each sample contains).
Saving and storing digital audio
Once a digital recording is made, it can be stored in a number of different formats. Each format has a different way to balance sound quality with the size of the digital file being created: extremely high quality recordings have not historically been practical in small music players, for example.
But as digital storage becomes more easily available with portable devices boasting many gigabytes of storage space, very high-quality digital audio is becoming a practical reality for millions of people.
A-Z guide to audio features
Dolby True HD
DTS Digital Surround
DTS Master Audio
Short for 5.1 channels, this is a way of providing surround sound to give a theatre-like experience. Five speakers plus a subwoofer are positioned around the listener, with each receiving a different channel as follows:
- Two front channels
- One front centre channel
- Two 'surround' channels
- One low frequency effects (LFE) channel
The subwoofer, which receives the LFE channel, can be placed anywhere in the room. Compared to a surround sound system without a subwoofer this saves space: because all the low frequencies are sent to the subwoofer, the other speakers can be smaller as they don’t need to produce bass. See also 7.1ch
An analogue recording stores the original sound by making changes to a physical medium, such as a magnetic tape or vinyl record. This is different to the way a digital recording is made.
The bit depth of a digital recording describes how many digits are used to store each sample of the analogue signal. The standard bit depth for CD audio is 16, with a sampling rate of 44.1kHz – this means that 44,100 samples per second are taken and each sample stores 16 bits of information. In general, a higher bit depth means greater sound quality but also a larger file size
Hi-Res Audio has a bit depth of at least 24 bits, with a sampling rate of 96kHz or above.
When sound is digitally it passes through a coder / decoder, or 'codec' for short. This is a piece of software or hardware that takes the analogue sound signal and 'codes' it into a digital format that can be stored electronically. When the audio is played back, the codec 'decodes' the digital file to produce sound.
Each audio codec uses a different method to encode the analogue signal, so they have different benefits and drawbacks when it comes to storing and reproducing sound.
Making a digital audio recording can lead to very large file sizes, which limits the practical uses of the technology – for example, how many songs can fit on to a digital music player. For this reason most audio file formats use some form of compression, stripping out certain sound information to reduce the size of the stored file.
The way that sound is compressed and decompressed when played back affects the final sound you hear. File formats where information is lost are called lossy. File formats that keep all the sound information or allow it to be reconstructed when played are called lossless.
Unlike an analogue recording, a digital recording changes the sound into a string of numbers that can be stored electronically (for example on a CD or hard drive) and then converted back to sound when played. MP3 is a popular digital file format.
A standard lossy audio format used for DVD and as a basic format for Blu-ray. Although it is a lossy format it is still good enough for use in cinemas. Compared to DTS Digital Surround the sound quality is lower, but the higher compression rate also means files are smaller and so Dolby Digital is more widely used.
Dolby True HD
DSD (Direct Stream Digital)
Direct Stream Digital (DSD) is a digital recording method with an extremely high sampling rate, beyond that of Hi-Res Audio and 64-128 times higher than CD audio. For some sound engineers this is as close as a digital file can get to the original analogue source. Some Sony Hi-Res Audio models are also capable of playing DSD format audio.
Digital Sound Enhancement Engine (DSEE) HX is Sony's unique upscaling technology. When digital audio in a compressed format is played back, DSEE HX replaces lost high frequencies in real time, giving near high-resolution sound quality. All audio played on DSEE HX equipment is enhanced, making you feel as if you're really there at the recording studio or concert.
DTS Digital Surround
A standard lossy audio format used for DVD and as a basic format for Blu-ray. Compared to Dolby Digital DTS Digital Surround has better sound quality, but it is less widely used because it produces larger files.
DTS Master Audio
High Resolution Audio typically refers to digital recordings with a sample rate of 96kHz / 24 bits or above. This gives sound quality that is much higher than that of CD or MP3 recordings – the standard CD audio format is sampled at 44.1 kHz / 16 bits.
When you see the Hi-Res Audio logo on a Sony product, you know that product has been designed to maximise the sound performance of High Resolution Audio. From portable music players to headphones, speakers and full home cinema systems, you can set up a full Sony Hi-Res Audio system.
Find out more about Hi-Resolution Audio
LDAC is an audio codec from Sony that allows you to enjoy high-quality wireless audio over a Bluetooth connection.
When audio is transmitted over Bluetooth, it normally uses the standard Bluetooth SBC codec, which can result in a loss of quality. LDAC transmits 3 times as much data as the SBC codec, maintaining high quality audio over Bluetooth and giving you an enhanced wireless listening experience for all your music.
A Low-Frequency Effects (LFE) channel is a separate audio track used for low-pitched sounds of between 3Hz and 120Hz – such as low, rumbling sound effects in film soundtracks. In a surround sound system this channel is usually sent to the subwoofer.
A lossless audio format stores digital audio in a way that either retains all the original digital information or allows it to be reconstructed when playing. Lossless audio formats include:
- DSD (DFF)
- DSD (DSF)
A lossy audio format deletes some information from the original digital recording in order to save space, while trying to preserve as much of the original sound quality as possible when the recording is played back. Each format strikes a different balance between compressionto save space and retaining information to preserve sound quality.
Lossy audio formats include:
Linear Pulse Code Modulation (LPCM) is the basis of digital sound recording. An analogue signal is sampled at regular intervals and its amplitude is recorded as a point on a digital scale. Because there is no processing or compression of the data, sound quality can be as high as professional studio masters – however, very large files are produced and so LPCM is not practical for everyday use.
The sampling rate determines the accuracy of the original digital stream
Sony's digital amplifier technology, uniquely developed for Hi-Resolution Audio to reduce distortion and noise at wider frequency ranges. Because S-Master amplifies digital signals directly – rather than converting them to analogue signals first – it maintains the purity of the original signal for more faithful reproduction.
Super Audio CD is a recording format developed by Sony to record sound in DSD format, surpassing the dynamic range that can be captured on a CD. Whereas the dynamic range of standard CD audio is 96db, that of an SA-CD is 120db. The sampling rate of SA-CD is 2.8MHz, 64 times that of standard CD.
Unlike normal CD audio, SA-CD supports 5.1ch surround sound as well as 2-channel (stereo) sound. SA-CD audio is encrypted for copy protection purposes, meaning it can be played through analogue, HDMI or i-Link output cables, but not through optical or coaxial cables.
When a digital recording is made from an analogue source, the sampling rate is the time interval between samples, and the higher it is the less is missed out. CD audio, for example, has a standard sampling rate of 44.1kHz, meaning 44,100 samples are taken each second.
In general a higher sampling rate means a higher quality recording. Hi-Res Audio has a sampling rate of 96kHz or above and a bit depth of at least 24 bits.
The standard audio codec for transmitting digital audio over Bluetooth. Because SBC is designed to prioritise efficient use of bandwidth above sound quality , it is not ideal for transmitting high-quality audio. Sony's LDAC carries three times as much data as SBC, allowing high-quality audio to be transmitted over Bluetooth.
In a 5.1ch or 7.1ch surround sound system, a subwoofer is a speaker that reproduces only low frequency sounds or the dedicated LFE channel. Because our hearing can't easily tell which direction low frequencies are coming from, a subwoofer can be placed anywhere in a room.
Because all the low frequencies are sent to the subwoofer, the other speakers can be smaller – so the overall system takes up less space.
5.1ch and 7.1ch surround sound are systems for sending separate audio channels to speakers positioned all around the listener, giving a richer listening experience. The .1 refers to the use of a subwoofer as an additional low-frequency speaker.
When a digital audio recording in a lossy format is played back, it is sometimes possible to fill some of the 'gaps' in the original sound by mathematically estimating where the original information would have been. This is called 'upscaling', as it can enhance the sound of lower-quality recordings to approximate high-quality audio.
Sony's unique DSEE HX algorithm upscales existing sound sources to near Hi-Resolution Audio sound quality.