DAXIn-DL

Digital Audio USB Interface - Driverless

The DAXIn-DL is a USB interface for connecting digital audio sources (S/PDIF or Toslink, with adapters also AES3) with a PC.

(Images of the prototype, click to view full size)

Highlights

No driver installation and no driver updates from the manufacturer required due to support by the operating system
Lossless (bit accurate) transmission of digital audio data into the PC
Compatible with the free audio recorder and editor Audacity and many other recording programs
sampling rates 8-192 kHz, resolution up to 24 bits
Complete galvanic isolation - no hum
Power supply from the PC

Technical specifications

Digital audio inputs:

S/PDIF coaxial, RCA, 75 Ohms, 8 kHz to 192 kHz, transformer-coupled
Toslink optical, 8 kHz to 192 kHz

Accepted sampling rates (kHz):

8

11.025

12

16

22.05

24

32

44.1

48

64

88.2

96

128

176.4

192

Deviations of about +/- 4% from the nominal frequency are accepted and displayed with the corresponding nominal frequency.

Resolution:

Windows^®: 8 to 96 kHz 24 bit, 128 to 192 kHz: 16 bit
Mac OS X^®: 8 to 192 kHz: 24 bit

Power supply: USB bus powered, 160 mA (USB-B connector)

Housing: 55 mm x 25 mm x 72 mm (W x H x D, without connectors), aluminum

USB Audio Class 1 and USB Audio Class 2

The DAXIn-DL operates at sampling rates up to 96 kHz always with 24-bit resolution in USB Audio Class 1 mode, which is supported by all operating systems.

Microsoft Windows^® supports only USB Audio Class 1, so that in Windows operating systems the higher sampling rates 128, 176.4 and 192 kHz are only available with 16 bit resolution.
Mac OS X^® (from 10.6, Snow Leopard on) and Linux support USB Audio Class 2, so that all sampling rates listed above are available with 24 bit resolution.

With a jumper next to the USB port it can be set how the DAXIn-DL shall connect to the PC at high sampling rates (128, 176.4 and 192 kHz):

In AC 1/2 position, the DAXIn-DL connects at high sampling rates with the PC at first in Audio Class 2 mode. In Mac OS X it is therefore immediately ready for use. In Windows no data transmission is possible. This is detected after 30 seconds, after which the DAXIn-DL connects again, but in Audio Class 1 mode. Thus in position AC 1/2, in Windows at high sampling rates, it will take half a minute longer until the DAXIn-DL is ready for operation.
In AC 1 position, the DAXIn-DL always connects in Audio Class 1 mode with the PC. Therefore, in Windows it is always immediately ready for operation. In Mac OS X, the full resolution of 24 bit would not be available at high sampling rates.

Conclusion:	Setting the jumper AC:
	Recommended	Disadvantage other than the recommended setting
Mac OS X:	1/2	Only 16 bits at high sampling rates
Windows:	1	Delayed connection at high sampling rates

Operation

Input selection and display: The input selection is automatic. When an input signal is present at both inputs, the optical input has priority. A LED indicates which input signal is transmitted.

Power indicator: Even if no input signal is connected, the COAXIAL LED indicates that the DAXIn-DL is supplied via USB.

When connected to the USB host (e.g. PC or laptop) the DAXIn-DL logs on as another audio device called DAXIn-DL XXXXX Hz, where XXXXX indicates the sampling rate received by the digital interface. When this sampling rate changes, the DAXIn-DL logs off and a few seconds later on again as a different audio device with the corresponding name resp. sampling rate.

In Windows and at sampling rates greater than 96 kHz DAXIn-DL XXXXXX kHz / 16 will be indicated.

The green LED S next to the USB connector on the back signals by slow flashing that the DAXIn-DL is ready for data transmission. It does not signal that the data transmission also works. It lights up constantly when the data transfer is taking place. It displays with dual flash that a connect with 128, 176.4 or 192 kHz was established to a Windows PC. It goes out briefly when the sampling rate of the audio signals is changed. The flashing stops entirely after 3 minutes without change of state in order not to disturb the user.

The DAXIn-DL is intended for recording on the PC. Playback must take place via another audio device on the PC.

Note:

This means that the signal from DAXIn-DL via USB is not directly audible on the PC under normal circumstances, i.e., it is not available in the playback controls. The signal can only be recorded and can only be heard during playback. This is caused neither by the DAXIn-DL nor by the operating system of the PC. It is caused principally by the digital technology: Correct reproduction of real time digital audio signals (e.g., signals from an ADC, TV or CD player) is possible only when the clocks of the source (ADC etc.) and the DAC run exactly synchronous. But the exact timing of the source is lost when the signal passes through a PC.

If playback via another audio device (i.e., another DAC, which necessarily runs with another asynchronous clock) is possible at all, it is therefore possible only with compromises. For this reason buffers are usually introduced, which on the one hand cause a delay of the output signal and on the other hand over time they may cause possible buffer overflows or underflows due to the asynchronous clocks. In these cases usually complete buffer contents are discarded in case of overflow or repeated at underflow, causing serious disturbances in the signal. Often such a signal path is therefore not even provided.

Depending on the operating system and the application program, it may be possible to make the audio signal from DAXIn-DL visible with a level meter. AUDACITY, which is mentioned below, can display the audio level. AUDACITY even offers the possibility to make signals from DAXIn-DL audible on another audio device outputs with the usual buffer delay and the possible overflow and underflow.

If necessary, we recommend for recording, editing and playback of files the free program AUDACITY (http://audacity.sourceforge.net/), which is free for Windows, Apple OS-X and Linux. This program offers much more than simply recording an audio signal.

A brief introduction to it will soon be here.

Version from 2016-04-13