How to run a bit perfect test with DirectStream

Written by Paul McGowan

We have a bitperfect test you can perform with your comper and DirectStream Here are the reasons why you might wish to do this:

There are multiple reasons people might want to have bit perfect transmission from their player to their DAC:

1) They want to play DSD via DoP

2) They want to send, DTS to a processor which decodes DTS into multiple channels.

3) They want to verify that the player or OS isn’t accidentally doing some sort of “evil” processing (e.g. upsampling)

4) They want to do the least “damage” to their audio

Different players have their own quirks and support for bit perfect playing.

JRiver MC has a very handy button in the standard views: it looks like a little three slider mixer it shows the audio path which gives a quick summary of what the heck is happening to your audio in JRiver. You are more on your own in Foobar2000.

Both JRiver and foobar2000 have support for things like ReplayGain. ReplayGain may break bitperfect playback but it is quite benign in the sense that when configured correctly it won’t “hurt” your audio EXCEPT if your DAC is only looking at, say, 16 bits. If you are playing DoP foobar2000 and JRiver bypass ReplayGain for DoP so there’s nothing to worry about there.

Foobar2000 has one volume control – it’s automatically bypassed for DoP so once again it’s not a problem when playing DoP.

JRiver on the other hand has an option to pick one of four different volume control implementations – be sure to pick the one that’s best for you circumstances, but some of them can break DoP bitperfect playing.

The more problematic volume controls are potentially in your OS. It’s often stated that an advantage of using ASIO drivers is that it bypasses the OS’s volume controls. This ISN’T TRUE for the drivers which come with the DirectStream. It’s also often the case that ASIO drivers are more twitchy than those of WASAPI, Kernel Streaming or Direct Sound. With DirectStream we provide USB drivers from Thesycon which are very good.

We prefer using ASIO for the DirectStream because the ASIO driver works and has fewer things to set up. But WASAPI or Direct Sound can be used successfully to do bitperfect playing as well. You need to do the following no matter which drivers you use: ASIO, WASAPI, Kernel Streaming or Direct Sound. I’ll only describe Windows 7 here because I don’t have any experience with recent Apple products and don’t have Vista or Windows 8 in hand.

In windows there are multiple places processing can mess things up. Here’s a quick walk thru of what to watch for. Open the Sound control panel. You can get there thru the start menu, or by right clicking on the little speaker icon in your taskbar tray and selecting Playback devices. In the sound control panel pick the Playback tab. In general you’ll probably want some other device than the PS Audio Perfectwave DSD device to be your default playback device. Select what you want and then click Set Default. Now find the PS Audio Perfectwave DSD device and click on it. Then select Properties. On the General tab you should have Device usage: Use this device (enable). On the Levels tab you should have the Speakers slider all the way to the right (so 100 is displayed there) and the mute icon set to unmuted (i.e. so there is no display of a little red circle with a line thru it.) Click on Balance and verity that both the left and right are at 100. Hit OK to go back to the PS Audio Perfectwave DSD device properties dialog. On the enhancements tab click Disable all enhancements. On the Advanced tab the critical items are that both Allow applications to take exclusive control of this device and Give exclusive mode applications priority are both selected. Hit OK to close the dialog. And another OK will close the Sound control panel. I repeat you need to do this no matter which drivers you use: ASIO, WASAPI, Kernel Streaming or Direct Sound.

The next things that can “break” bitperfect playing are some settings in the players or the drivers. Direct Sound has the capability of fading the end of an item down, fading the beginning of an item up and/or crossfading two items together. During these fadings the output won’t be bitperfect. I recommend not using the Direct Sound fading options if you want clean transitions or gapless playback of DSD. Similarly some players offer fading or other transitions when starting, stopping, seeking, etc. For a good DSD experience turn all of these fading features off.

To check that all of this has been done correctly we provide a bitperfect test. It’s a special flac file that you can play. You can download it from the PS Audio web site by going to the software section of our Downloads page. When DirectStream sees exactly the correct pattern, it displays a green check mark and the words Bit Perfect near the upper left of DirectStream's display. You should probably mute your preamp or set DirectStream's volume to 0 when you run the bitperfect test, but the level is low and shouldn’t hurt anything if you forget. Since DirectStream can’t possibly know when something in the playback chain changes, the bitperfect display goes away as soon as the test signal stops. If you wish you can put the bitperfect test file on track repeat and then look for the Bit Perfect display as you adjust the player’s or the OS’s playback options. The Bit Perfect display may go away for a second when the track loops.

Some other thoughts – with DirectStream you should feel free to use the digital volume control or ReplayGain features of foobar2000 or JRiver MC. They won’t significantly affect the sound quality since DirectStream receives 24 bits even if the source only has 16 bits. A quick and dirty check for bit perfect playing is to play a 16 bit track and see if the number of bits indicated on DirectStream's display is indeed 16 bits. If any volume control, DSP, Replay Gain, etc. is active the screen with probably read 24 bits.

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