File format

Unlike a codec, a file format is usually instantly obvious (see codec for more information). On most operating systems, such as OSX and Windows, the file type is determined by the last letters after the dot in the file name. When you are looking to playback video or audio files on a system, be aware it must support both the file type and codec. For example, an AVI movie file could have any codec from a large list, including DivX and XVid (among others).


Freesat is the subscription-free satellite TV service that gives you a whole host of benefits. The service uses the same satellite as Sky Digital, so if you are switching over you will not need to reposition your dish. The advantage of Freesat TV is that it offers great reception no matter where you are. Unlike TV over-the-air (see digital tuners), the only thing that will limit your reception are trees, large buildings or other structures that can obscure your line-of-site to the satellite. This makes it ideal for those with reception issues in aerial black spots.

A Freesat tuner can either be in-built on a TV or accessed via a separate set-top box. For recording, look out for the Freesat+ logo - this provides storage space with capacity to record, pause and rewind live TV. Once tuned in, you will be treated to a wide range of both standard and HD channels, including great entertainment, news and children's entertainment. Many Freesat devices also offer catch up TV, as well as smartphone and tablet apps to control what you are watching, such as Freesat Freetime.


If you've got an aerial for watching TV, Freeview is what you'll pick up. As well as offering a wide selection of subscription-free TV and radio channels, there are also some that you can unlock with a subscription, without needing a new box. For those with a satellite dish, Freesat is your option if you want to avoid monthly costs.

Freeview HD

As well as offering over 70 channels, Freeview also offers, at time of writing, up to 15 channels in incredible HD quality, still completely subscription-free. If you want to receive these you'll need to check that the TV or recorder you're buying is Freeview HD compatible, though the vast majority now are.

Freeview Play

Freeview Play is a Smart TV service by the people who originally brought digital TV to the UK. It offers the same channels as Freeview HD, but with added catch-up services. Like all Smart platforms it does require a good internet connection, however it receives its live TV signal through a standard TV aerial. An advantage of Freeview Play over other systems built into certain manufacturers Smart TVs is the fact both catch-up and live TV features on the same guide.

Frequency range (audio)

Like any other wave, sound waves have a frequency or how many times they repeat every second, measured in Hertz (Hz). The human ear can hear sounds from, depending upon the individual, 20Hz to 20,000Hz (20 kHz). Low sounds, or bass, come in at the bottom and high sounds (treble) live at the top, with the space between referred to as the mid-range. Electronics, speakers and headphones usually list a frequency range in their specification, which gives you some indication as to the performance, though a demo will tell you much more about how they sound (see running in (speakers) for more information on getting the full frequency range from your speakers).

Gracenote CDDB

Ever put a CD into a computer and wondered how it knew what album it was and the track titles? The answer is most likely the Gracenote CDDB (CD Database), a massive online archive that's constantly updated by users. As well as being used by music software like iTunes, it's also built-in to most music servers.

Hard Disk Drive (HDD)

Internal storage, such as that found in your computer, that holds large amounts of data. They're also commonly found inside recorders and music servers. As a rough guide, an hour of recorded video takes up around 2GB in standard definition or 4GB in high definition. For music, each 1GB is enough for about 20 albums in MP3 quality or 4 at CD-equivalent lossless quality. Mobile phones and tablets can often access the data, such as music and video files, on them quicker as they use solid-state drives (SSD), which have a quicker access time.

Hard disk drive recorders

A component that can record to its own internal space without requiring discs or tapes so you don't have to hunt for free space on a disc whenever you want to record something. You get other advantages too, like being able to easily edit out ad breaks, for example. One popular specific type of HDD recorder for recording TV broadcasts is the personal video recorder (see PVR for more information).

HDCP (High-bandwidth Digital Content Protection)

This system is designed to prevent unauthorised copying of data. In the early days of HD, some legitimate equipment wasn't compatible and caused issues, but this is no longer an issue. Put simply, as long as you're not trying to breach copyright, you won't have any problems. HDCP 2.2 is the standard equipment needs to support to be able to playback 4K Ultra HD content, be it Ultra HD Blu-ray players, 4K TVs or set top boxes.

HDMI (High Definition Multimedia Interface)

The digital successor to SCART, a single HDMI cable can carry high definition pictures, surround sound audio and remote control info between two devices. Nearly any video source you buy now has an HDMI output, from TV set-top boxes to games consoles to Blu-ray players and even laptops and cameras. Home cinema amplifiers also have multiple HDMI ports to act as a video switcher for your TV or projector.

HDMI 2.0

HDMI 2.0 is an enhanced version of HDMI using the same connections but offering many technical advantages. These include the ability to handle 50/60 frames per second from 4K signals, 48-bit/pixel colour, 32 channel surround sound, full 21:9 aspect support plus much more.

HDMI 2.1

HDMI 2.1 builds on the 2.0 version. It supports higher resolution and refresh rates, making it the default standard for 8K TVs and sources. HDMI supports Ultra High Speed HDMI cables, cable of carrying the full 48 Gbit/s bandwidth required by 8K and even up to 10K resolution. HDMI 2.1 also supports Enhanced Audio Channel (see eARC). .

HD Ready

A badge to denote screens that can accept and display 720p/1080i High Definition pictures. Over time, this term has come to mean a TV with a lower resolution than 1080p, (which is often referred to as 'Full HD'). Common on smaller screens and some budget models, you'll still see a big improvement in high definition from standard definition pictures with these screens, though you won't see every last detail from sources such as Blu-ray (1080p) discs, or Ultra HD 4K.


HDR stands for High Dynamic Range and, in this instance, greatly enhances a TV’s picture quality. HDR offers brighter whites and darker blacks for more dynamic image quality. You’ll also notice more detail within the darkest and lightest areas of the image – such as the texture on the inside of a cave wall. This feature also makes HDR hugely popular with gaming fans, as you can seek out foes lurking in the darkest areas of the game!


HDR10 is the next generation of HDR. HDR10 is widely supported by movie producers and features on Sony’s PlayStation, Xbox One and Apple TV platforms, making it more widely available than the rival Dolby Vision (see Dolby Vision above). It uses wide-gamut Rec. 2020 and a bit depth of 10-bits for rich, life-like colour.


Also known as HDR10 Plus, HDR10+ was announced by Samsung and Amazon Video and improves upon HDR10 by adding dynamic metadata to adjust brightness on a scene-by-scene or frame-by-frame basis. Controlling the colour more accurately creates a more natural image that’s brighter only when it needs to be. This means it’s much closer to the similar Dolby Vision system. As with Dolby Vision, however, not all TVs and sources are compatible, so you’ll need to check this.

Headphone Amplifier

These are the best way to enjoy the best possible sound from your favourite set of headphones. Dedicated headphone amplifiers are specifically designed to provide maximum power output with minimum distortion. Much like stereo integrated amplifiers, headphone amplifiers come with a variety of features and specifications. Higher current outputs drive high-end headphones that require more power, and hand-held versions have built-in batteries for ideal portability. Some versions also come supplied with built-in DACs [Digital to Analogue Converter], to extract every last detail of sound from digital sources.

High definition (HD - video)

At its most basic level, HD (high definition) means better quality pictures. It is both a broadcast technology and a screen resolution, and there are several signal types including 720p and 1080i. Any screen implementing these standards is called 'HD ready'. The next level up, 1080p, is sometimes called Full HD. Above this resolution is Ultra HD (4K), which gives resolutions four times higher than 1080p.

High resolution audio (Hi-Res)

High Resolution Audio provides exceptional sound quality from High Resolution music files. Typically these are DSD, WAV, AIFF, FLAC or ALAC files at 24 bit/96kHz, 24 bit/192kHz or higher rates. Think of it like High Definition TV for your audio and the difference is easy to hear.

Home Cinema

Home cinema has come to be a catch-all term for a system that plays music and movies with a TV or projector and an external speaker system of some kind, usually surround sound. The whole idea is to recreate as accurately as possible the picture and sound quality of a cinema auditorium. Filmmakers want their work to be showcased in all its glory, with not a line of dialogue missed or a pixel out of place and a home cinema is just the tool for the job - in fact, you'd be surprised at how easy it is to build a seriously impressive system.

IMAX Enhanced

A collaboration between IMAX, DTS and award-winning Hollywood sound mixers, IMAX Enhanced certification delivers stunning levels of sound quality. Only the highest quality home cinema equipment meets the standard. IMAX enhanced content is found on certified HDR streaming and UHD Blu-ray and promises to offer the next step-up in sound from the already impressive DTS:X.

Impedance (speakers)

This is the load a speaker brings to bear on an amplifier or its electrical resistance, measured in ohms. The higher the impedance - with 8 ohms being the norm - the easier the speaker is to drive or power, meaning the speaker should still work well with less power. If a speaker has consistently low impedance - say 4 ohms - the speaker is much harder to drive. It's important to make sure your speaker's impedance is above the minimum specified by your amplifier. If you connect two pairs of speakers in parallel the impedance halves, meaning that two sets of 8 ohm speakers present a 4 ohm load to your amp.

Internet Radio

In its truest form, this is simply a device that allows you to stream radio stations through the Internet by connecting to your home network. Because the device is connected directly to the web, it doesn't rely on localised radio signals to pick up stations - instead you get access to thousands of radio stations from all over the world. Also, because an Internet connection has better bandwidth, sound quality and signal reliability tend to be better than digital radio (subject to the codec and bit rate used by the station).