Bit Perfect Audio

In the last year or so, there has been a flood of standalone digital to audio converters (DACs) that are aimed at personal computer owners who want to improve the reproduction of their music collection stored on computer hard disks. Standalone DACs were all the rage in the mid nineties as they offered a reasonably priced upgrade to compact disk owners without having to replace the whole player providing it had a digital ouput socket which could then be fed to an external DAC.

The same situation now exists with PC’s as the majority of soundcards all provide digital outputs as analogue output. However the analogue output is usually of a poor standard due to widespread use of poor components such as cheap and nasty DACs, not to mention reliance on a PC’s power supply which is not designed for audio applications and is critical if any sort of true hi-fi reproduction is to be achieved.

Therefore it makes more sense to feed the digital output of a PC to a dedicated external audiophile DAC to achieve the best sound quality which leads us on to the topic of this post. One of the most least explained facts about digital audio and one that seems to escaped the various magazine reviews and manufacturers’ promotion material surrounding these new external DACs is question of bit perfect audio, that is that the digital output from the computer soundcard is the same as the digital output from the stored audio file.

Firstly there are two things to understand about a standard PC audio set up, one is the way the PC’s operating system handles and mixes sound from applications and the second is how the soundcard handles and mixes sound.

With regard to the PC, if you take Windows XP as an example any audio file “ripped” from an audio CD will never be bit perfect audio when it reaches the computer’s soundcard because the XP operating system has a component called the Kmixer which up-samples all audio to 16bit/48khz so all the inputs have a common sample rate unless all inputs bar the wave input are muted. Anyone with experience of handling digital audio files will tell you that it is not ideal to up-sample from 16 bit 44.1 khz (CD standard) to 16 bit 48khz. Even with all inputs muted so that Kmixer works at the rate of the outputted music, it still performs DSP on the volume levels and is not bit perfect.

Therefore in order to achieve bit perfect audio, the kmixer must be bypassed which in XP usually means using ASIO drivers or kernel streaming which is supported by WinAmp and Foobar, but sadly not the native Windows Media Player which I personally prefer for its usability and integration to the operating system. What many people don’t know is that there is a way to bypass the kmixer and use Media Player by using a program called Re-Clock that can configure all audio to use Kernel Streaming and hence send bit perfect audio to the soundcard. The other handy feature about Re-Clock is that it tells you exactly at what frequency and sampling rate audio is sent to the sound card. You will know if kernel streaming is working because the wave volume control in the mixer will no longer operate. The use of kernel streaming naturally not only improves digital output but also analogue output because you have removed an unnecessary re-sampling stage (and this also applies to multi-channel audio from DVD software).

The next stage of the quest for Bit Perfect Audio, is to be aware that not all soundcards support bit perfect audio (i.e they cannot output 16/44.1 audio cleanly without some sort of re-sampling), so no matter how sophisticated your shiny new DAC is, it will never sing to its potential, due to the quality of its digital input. A good example of this the Soundblaster Audigy Cards that can output a 16/44.1 digital signal but due to the design of the on board digital signal processing chip (DSP), all sound is first up-sampled to 16/48 and then down-sampled to 16/44.1 if you want to output CD sample rate sound from either a disc or a file. The good news is that there are soundcards available for under £20 which will output bit perfect sound providing they are used with the right drivers.

So before anyone contemplates buying an expensive DAC to complement their PC based music collection, please check thoroughly that your soundcard supports bit perfect audio or alternatively read these posts below for details of a windows based solution that guarantees bit perfect audio.

Bit Perfect Audio part 1
Bit Perfect Audio part 2
Bit Perfect Soundcard

This entry was posted on Saturday February 14th, 2009 at 8:00 PM and is filed under Tweaks. You can follow any responses to this entry through the RSS 2.0 feed. Comments are now closed.