The arrival of high-definition Blu-ray discs introduced us to a new set of audio formats - and, with them, a whole new set of potential problems. Find out here how to side-step common errors associated with DTS-HD, Dolby TrueHD, and Secondary Audio.

Players from different manufacturers don't always handle the various Blu-ray audio formats in the same way. Pictured here is the Pioneer BDP-320, for around 350 GBP.

Things are always going wrong with the sound on Blu-ray players - and it's no surprise, given that there are four new audio standards, a new type of digital connection, and heaps of new audio features. In this article, we explain common Blu-ray sound problems - and, of course, we offer advice on how to solve them.

Even just checking the current audio format on the player can be confusing. But this is a very important question - after all, you need to know if the desired level of quality, such as Dolby TrueHD, is actually being reproduced.

First, you need to make sure that only the device doing the decoding can identify the format. Once the decoding is complete, all you'll have is uncompressed multichannel audio, and you'll no longer be able to see what the signal's original format was - and that's the case regardless of whether it arrives to the AV receiver or pre-amp in analog or digital form. Neither PCM via HDMI nor analog signals via a 5.1- or 7.1-channel input carry an indicator of where the sound is coming from.

Blu-ray playback on the old PlayStation 3 therefore serves to irritate many users, since the console will only output the high-definition audio formats if you let it do the decoding itself. The new slim version of the PlayStation 3, on the other hand, outputs HD audio correctly as a bitstream.

If a player bears these logos, then it also has to have the corresponding decoders.

If you want to know which audio format is currently in use, you'll have to ask the Blu-ray player. Most players have an audio button on the remote control that displays the current audio track; repeated pressing will usually cycle through the available tracks. If the player and the receiver are displaying the same format, the decoding will be taking place in the receiver; in this case, the HDMI audio wire is carrying the bitstream to the receiver. If the receiver's display shows the letters "PCM", the player has already done the decoding. There's one exception: If the Blu-ray disc itself contains PCM sound, neither the player nor the receiver will have to decode it.

Some players, such as the Sony BDP-S 550, will only transmit an HDMI bitstream if the AV receiver has a built-in decoder.

Some Blu-ray players have a nasty habit of leaving the user no choice in terms of audio format - they simply decide for themselves. Players such as the Sony BDP-S 550 offer no choice of HDMI transmission type if the attached receiver can decode a bitstream. This is no problem in itself, since a bitstream is actually the best way to transmit the signal. But it can lead to uncertainty in terms of the player's abilities - as it did in our review of the aforementioned Sony player, since we no longer had a receiver that couldn't decode all audio formats.

Those looking to buy a player should bear in mind, therefore, that the results seen in an in-store demo won't always perfectly match those on a home system. If the store uses an AV receiver with no HD-audio decoder, but with a multichannel input via HDMI, the player's built-in decoder will be active. Even with players that allow you to switch the output type, you shouldn't jump to any hasty conclusions, since PCM and bitstream cannot be compared in this way - simply too many other factors are involved.

It's well known that you get the best Blu-ray sound via HDMI - generally in the form of Dolby TrueHD or DTS-HD, and specifically as a bitstream, where possible, since this limits the potential for error during transmission. As a second best option, we recommend multichannel PCM audio, which is accepted by almost all HDMI-equipped receivers.

If there's no HDMI input on the receiver, you'll have to revert to the analog inputs. This will work if the player offers the necessary settings, such as speaker size and listening distances. Otherwise, the receiver's speaker settings would also have to apply to the analog input - and this isn't always the case. And you should always ask yourself if the normal audio tracks, such as Dolby Digital or DTS via S/PDIF, don't sound better. If in doubt, compare the two options for yourself.

Have you ever wondered why the sound takes so long to come on at the start of a movie? Even once the opening sequence is long since over, you often still can't hear anything. We've even noticed the same effect with discs' extras. But you shouldn't immediately assume that something's broken; actually, these delays occur because of the number of different audio systems present on Blu-ray - crucially, there are more than the player's memory can hold. This means the player first has to load the suitable algorithms before it can begin decoding the sound.

The terms ‘audio mixing' and ‘secondary audio' refer to a nifty special feature. Often, the secondary audio is switched on simply by ticking a box in the audio menu, but this small step can have big effects: Activating it mixes the movie soundtrack with other sources - the menu's click noise, for example, which announces each button-press on the remote control. There are also audio commentaries; these need no separate soundtrack on Blu-rays, since the commentary can simply be superimposed on the normal movie sound. Incidentally, this also applies to the extras that you can download from the Internet - you can also simply add them to the movie's sound.

This is quite complex technically, because Secondary Audio adds another audio format, DTS Express, which isn't permitted for actual movie sound. This means more work for the player, since it has to decode both audio streams and convert them into PCM format. But that's by no means the end of it: It also has to adjust the sampling rates and bit-word lengths before all of the sound can be combined. Once this is done, the next, important decision is already knocking on the door: How should I output the audio signal? In most cases, you can just leave it set to PCM - at least, you can whenever there's a successful HDMI connection. It's also generally no problem to output sound via the analog multichannel connections.

Things get difficult when it comes to the normal digital outputs (optical and coaxial), since, in these cases, digital multichannel sound can only be transmitted in Dolby Digital or DTS. Most players have their own encoders for these, and can produce the signals from the decompressed PCM audio. But it's rarely possible to predict what the result will be when the signal contains a mix of various standards. For example, the S/PDIF output can deliver Dolby Digital, even if the audio on the disc is only in DTS.

What generally doesn't work is outputting the mixed audio as an HD bitstream. This is sometimes because outputting DTS-HD or Dolby TrueHD requires too much effort. But equally realistic is the possibility of a copy-protection system intervening - Hollywood secures and keeps a close watch on anything that involves high-definition material.

There are other peculiarities with Blu-ray players - some allow you to force a bitstream output, for example. On others, switching the audio format will automatically activate or deactivate the secondary audio - often entirely unnoticed by the user, since the player makes no attempt to inform them. So, if a player is behaving oddly, make sure you keep these stumbling blocks in mind while trying to track down the cause.