Marantz PC Manual download pdf (Page 13)

MARANTZ GUIDE TO PC-AUDIO | NA-11S1 | 05.2013 | 13www.marantz.eu

AUDIO TRANSMISSION MODES

Looking for bit perfect sound! – Audio transmission modes

explain in details

Windows: direct sound

It’s the standard playback mode on a Windows PC.

It goes thru the kernel mixer, that acts as an interface of the OS

kernel between the various sound sources in a PC (PC sound, MIDI,

players, etc…) and the sound card’s driver. All the various sources

can produce sounds with different sampling frequencies; the kernel

mixer will resample all the various audio streams to a unique sam-

pling frequency and allows them to be mixed before sending them

to the audio card. But this mix will be at a low frequency (standard

44.1 kHz). On top of this the mixer will add some treatment (dy-

namic compression, tone control, loudness control, etc…) so this

will generate a low sound quality.

For this reason, we should avoid direct sound mode for the best

sound quality.

This is not bit perfect

Windows: kernel streaming

Kernel streaming is the “audiophile” playback mode for Windows.

Standard players such as WMP or iTunes do not support this mode

at the moment, so a dedicated media player is required. The audio

data will be sent from the media player directly to the USB-DAC,

by-passing the audio mixer. This will also need less CPU power. So

your PC will be more stable and generate less Jitter (less errors).

Now we have a so-called bit perfect sound. Kernel Streaming is

often used on PCs running Windows XP.

Windows: WASAPI

WASAPI (Windows Audio Standard API) was developed for Vista

and Seven to replace Direct Sound. WASAPI isn’t intended to work

on Windows XP. Standard WASAPI will make use of the Windows

Sound Mixer and is not bit-perfect.

Windows: WASAPI Event Style

WASAPI Event Style is the bit-perfect version of WASAPI and will

by-passed the audio mixer. The sound quality obtained using

WASAPI Event Style is comparable to Kernel Streaming mode.

WASAPI needs a bit more CPU power than plain kernel streaming.

But, WASAPI gives access to a bigger choice of players.

WASAPI Event Style is bit-perfect.

Windows: ASIO and ASIO4ALL

ASIO means Audio Stream Input / Output and is another method to

bypass the Audio Mixer and in addition the Kernel, to let the media

player directly talk to the USB-DAC. ASIO was built for XP but it

works on all OS. ASIO was created to overcome the USB Audio 1.1

limitations. On USB 1.1 only 48 kHz/16bit in direct sound mode was

possible, but with ASIO 96 kHz/24bit.

ASIO is bit-perfect.

Mac OS: Core Audio

Core Audio is the Mac equivalent for the Windows Audio Mixer

and handles any kind of audio information – input and output. Core

audio works in floating point like WASAPI, a double conversion is

necessary, on both player and driver side.

Core Audio is not bit-perfect

Mac OS: “hog mode”

The difference between Core audio and hog mode operation is

that Core audio allows more than one client to access the driver at

the same time. The Core more mode will have the same issue that

we already see on the Direct Sound streaming in windows so we

will lose sound quality. To avoid this, on Mac we will use the “hog

mode”. The “hog mode” needs to be activated in the Media Player.

The mode will allow the player to get first priority when started and

block all other audio devices, so in this case we will get the best

sound without any mixing processing.

MAC Integer/mode

Addressing directly the HAL [AppleHAL_2] gives the possibility to

bypass the two main overhead

Processes of the above standard mode:

• Mixing buffer

• Float to DAC native format conversion

In Integer Mode the player software supplies a stream already

formatted in the native DAC format.

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