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USB DAC GUIDE TO COMPUTER-AUDIO | 12.2015 | 5

Media

Player

Mixer

Computer

Sounds

Kernel Driver

PCM/DSD

stream

UBSDAC

And ultimately, the incoming signal to the DA converter may be very dierent than

it was initially. In addition, there are various interference phenomena due to the

mixer that allows dierent programs to play sound at the same time (mail coming

in when you listen to music for example) and it’s also related to the environment

and highly disturbed electrical computer.

Let’s have a look to the complete chain.

A lot of devices which can have an inﬂuence.

Of course: not to forget about the cable between PC and external DAC.

The ﬁrst 5 boxes represent the PC while the last box is the USB-DAC.

1. Media player – software running on your computer to play back the

audio ﬁles

2. Mixer – this one will add the Windows Sounds to the original signal

(if not by-passed)

3. Kernel – handling all the process to transfer the digital audio signal

4. Driver – ensures the audio signal will be properly transferred to the USB

output in asynchronous mode (USB-DAC deﬁnes the clock and timing of the

audio package sent)

we will need a bit-perfect is a player that will allow sending the com-

plete data bit-to-bit without skipping or modifying any of the original data.

So we will get the integer signal from the original ﬁle. Standard media play-

ers such as iTunes and Windows Media Player do not support bit-perfect

transmission. Furthermore, they have limitations on the playable ﬁle formats.

That’s why we recommend players like jRiver Media Center for PC and Mac and

Audirvana (time being Mac only). Other software media players are available on

the market, but we like to focus on these two for now as they support not only

PCM- Signals but DSD streaming as well.

For the Bit-Perfect transmission we need to make some setting on the comput-

er and the Software Player to get everything working together smoothly. These

settings will allow us to bypass the Windows Sound Mixer (see below graphic)

and on Mac we will give the priority to the audio sent to the player over any other

sound.

These settings will aect the Audio Output Mode and key technologies here are

Kernel Streaming, WASAPI and ASIO, beside others.

The goal is to use the Bit-Perfect mode also known as “Bit-transparent” mode.

This means that all the data of the audio ﬁle is exactly the same as received in

the USB DAC. Note this is not possible with any USB-DAC. The DAC, needs to

support this too.

We also need a driver for the USB DAC (only for PC)

For a PC, the driver is very important and you need to install it before connecting

your USB DAC to your computer. For Mac operation there is no dedicated driver

installation required for most of the DAC’s. However this might be dierent for

other USB-DAC devices.

The Driver will allow the USB DAC to control the clock, so the rhythm in which it

receives the audio information. This is called Asynchronous mode and is need-

ed to avoid Jitter, which deteriorates the signal quality. It will also give important

information to the PC about the speciﬁcation of the connected USB-DAC. Once

the driver is installed on the PC the USB-DAC can be directly selected in the

software media player as the output device (soundcard).

There is a need for a good USB cable to connect the player to your Com-

puter. It is not recommended to use a cable longer than 5m. And the quality of

shielding will also have some inﬂuence on the sound quality. It is recommended

to test several cables to optimize performance.

Audio handling inside a PC

To better understand this, take a look at the audio-handling diagram below –

From the Media Player the audio will be send by Direct Sound, the default setting,

through the Mixer, while Kernel Streaming, Asio and Wasapi bypasses it. The

dedicate driver installed will allow the USB DAC to take the lead for the data re-

quest – this is called Asynchronous Mode.

Just for the PC environment the Media player, for example JRiver, default setting

is Direct Sound and uses the Mixer. So it is necessary to change the setting to

Kernel Streaming, WASAPI or ASIO streaming.

NOTE: Any mode, WASAPI, ASIO or Kernel streaming, does have some inﬂuence

to the sound characteristic. Please listen carefully to ﬁnd the appropriated mode

for your system.

Media

Player

Mixer

Computer

Sounds

Kernel Driver

PCM/DSD

stream

UBSDAC

AsynchronousMode

DirectSound(DS)

KernelStreaming(KS)

WASAPI

ASIO