A Quick Guide in Understanding Digital Audio
If you're confused with some languages used to describe audio equipment, here's a quick guide to help you with some of the common terms and settings.
How Digital Audio is Recorded
Since 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 constantly expand 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, and this creates 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 to Save and Store Digital Audio
Once a digital recording is made, you can store it in a number of different formats. Each format has a different way to balance sound quality with the size of the digital file created, and extremely high quality recordings haven't historically been practical in small music players. However, as digital storage becomes more easily available with portable devices, it will boast gigabytes of storage space. As a result, high-quality digital audio is becoming a practical reality for millions of people.
5.1ch is short for 5.1 channels. This is a way to provide surround sound a theater-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 center channel
- Two surround channels
- One Low Frequency Effects (LFE) channel
Note: 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.
A 7.1 channel surround sound system uses seven speakers, plus a subwoofer. It is similar to a 5.1ch system but with two additional surround channels.
An analogue recording stores the original sound, which makes changes to a physical medium, such as a magnetic tape, or vinyl record. This is a 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.
Sound or audio signal digitally passes through a coder or decoder, or codec for short. Codec 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 and produce 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 a digital music player can store. 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.
Dolby Digital is 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. The higher compression rate also means files are smaller, and so Dolby Digital is more widely used.
Dolby TrueHD is a Lossless audio compression format similar to DTS® HD Master Audio. Both are used as optional sound formats for Blu-ray Disc.
Direct Stream Digital (DSD)
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 products are also capable of playing DSD format audio.
Digital Sound Enhancement Engine (DSEE) HX
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, which produces a near high-resolution sound quality. All audio played on DSEE HX equipment is enhanced, which makes 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 HD Master Audio
A Lossless audio compression format similar to Dolby TrueHD. Both are used as optional sound formats for Blu-ray Disc.
DTS:X is a surround-sound audio format designed to compete with Dolby Atmos format. It is an immersive audio standard, created to let you feel closer to the action with the help of Height Channels, providing an effective visualization seeming to surround the audience, so that they can feel completely involved.
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 maximize 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.
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 three 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.
Note: A separate article about LDAC is available.
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 played. 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, but preserves as much of the original sound quality as possible when the recording is played back. Each format strikes a different balance between compression to save space and retains information to preserve sound quality.
Lossy audio formats include:
- Dolby Digital
- DTS Digital Surround
Linear Pulse Code Modulation (LPCM)
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.
This is 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 (SA-CD)
SA-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, which means 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.
Standard Audio Codec (SBC)
This is the standard audio codec for transmitting digital audio over Bluetooth. Because SBC is designed to prioritize 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 to mathematically estimate 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.