Lab

Hard disk/DVD combo PVRs

The digital TV switchover has started, and soon we'll all be exclusively watching digital TV. Many of us have already bought set-top boxes to receive the wide range of new channels available, but to make the most of the Freeview service and your television licence fee, you need a digital TV hard disk recorder.

A hard disk recorder receives digital broadcasts like a normal set-top box, but it can also record up to 125 hours of programmes on its internal hard disk. Personal video recorders (PVRs) can even pause live TV, so you'll never miss a moment of your favourite programmes again.

These great features can be had for as little as £100 including VAT, which is a lot less than the cost of a year's TV licence. This month we've reviewed six hard-disk PVRs and three with both hard disks and DVD writers so that you can back up your recordings. Read on to find the perfect way to record the upcoming flood of Christmas TV.

There are two types of digital TV recorder - or personal video recorder (PVR) - on the market. The most common type stores TV programmes on a built-in hard disk, but you can also buy models that provide both hard disks and DVD recorders. This buying guide will help you choose which type of PVR, and which model, is best for you.

Tuner stakes

All the hard disk-only PVRs in this month's Labs have twin digital tuners. This makes them ideal for plugging into TV sets that can't receive digital broadcasts. With two tuners you can record one programme while watching another, or even record two at once. Having both tuners in one device also means that you need only one remote control to handle all your TV viewing.

PVRs with both a hard disk and a DVD recorder function more like traditional VCRs. They have only a single digital tuner, so you'll have to use another set-top box, or a television with a built-in digital tuner, if you want to watch one programme while recording another. The combo PVR's main advantage is that you won't need a separate DVD player, and you can archive your TV recordings to DVD if you want to keep them in the long term.

Pass the ports

All the PVRs have RF inputs for connecting an aerial lead. They also have RF passthrough ports, which enable you to pass the aerial signal on to your television or VCR. This passthrough usually carries the original RF signal rather than decoded digital TV, but Topfield's PVR also carries a decoded signal for use with older TVs.

To watch digital programmes you'll need to connect the recorder to your TV with a video cable. All the TV recorders in this Labs test have SCART sockets for this purpose, and you'll get the best picture if you plug them into an RGB-capable SCART socket on your TV. Your TV's manual will tell you which of its sockets are RGB-capable and how to enable RGB mode for each socket.

If your TV has only one SCART socket and it's already connected to a VCR or DVD player, you can simply plug that device into the second SCART socket on the PVR. The PVR will then pass the signal on to the TV when the PVR is in standby mode. PVRs can sometimes use their second SCART socket to output recorded material to a VCR for archiving.

If you're connecting a high-definition LCD or plasma TV to a PVR with combined DVD and hard disk, then you should use either a component or HDMI output. All the DVD/hard disk combos here will upscale DVD and TV broadcasts to high-definition resolutions. See the individual reviews and the table on page 105 for more details.

Picture quality

The picture quality of digital broadcasts varies considerably. Channels are broadcast in small groups called multiplexes, and each of these has a limited bandwidth. Programmes are compressed using MPEG2 compression, and different channels are assigned different amounts of bandwidth. BBC1 generally has consistently high video quality, so we used this channel for our testing.

There is little variation in the picture quality of recorded programmes between different PVRs. All the hard disk-only devices record programmes exactly as they are broadcast. However, the hard disk/DVD combo PVRs have built-in video encoders, so you can reduce video quality to save space on your hard disk or fit more video on a DVD. In our tests we found that leaving the hard disk recorders at their default quality settings gave by far the best results. When we reduced the quality we experienced significant compression artefacts.

Due to the varying amounts of video and audio data in broadcast TV, it's very hard to say exactly how much TV a hard disk will store. As a guide, you'll get around half the hard disk's total capacity in hours, so a 250GB hard disk will store at least 125 hours of programming. Inexpensive single-layer DVDs hold 4.7GB, so you'll get around two hours on a disc at optimum quality. This means you may have to reduce the quality to fit a long film on a single disc.

Pausing TV

Another advantage of having a hard disk recorder is the ability to timeshift live TV broadcasts. This enables you to pause the programme you're watching when you want to make a cup of tea or answer the phone. The PVR puts the ongoing broadcast into a buffer, which you can then watch or rewind. On some PVRs this buffering process is constant, and the buffer is refreshed when you change channels, while on others you have to activate timeshifting first. See the reviews for details on how each recorder deals with timeshifting.

Electronic Programme Guide

The electronic programme guide (EPG) is one of a PVR's most useful features. Rather than fiddling around entering the date, channel, time and duration for each programme you want to record, you simply find the programme on an easy-to-understand timeline and press record. The recorders download these listings automatically from TV broadcasts.

Each electronic programme guide in the group works differently, so we've made detailed notes on each in the individual reviews. We've also noted which EPGs allow you to make simultaneous recordings, how they deal with recording conflicts and whether they enable you to record an entire TV series with a single button press.

Viewing cards

Some of the hard disk recorders have slots for conditional access modules, or CAMs. These modules can accept viewing cards that provide access to subscription services, such as Setanta Sports or Top Up TV Anytime. Although these are currently limited in number, you can expect more to appear over the next few years. A CAM and card for Setanta Sports will cost around £40. The Top Up TV recorder has a built-in CAM and so can accept a card straight away.

Data files and DV capture

As well as playing DVDs, the DVD/hard disk combo PVRs have a number of other tricks up their sleeves. They all have analogue video inputs and FireWire ports for capturing footage from camcorders and burning it to DVD. Some devices also have USB ports for accessing media files on removable storage devices or digital cameras. See the individual reviews for more details.