USB

Overview

The term "USB" is used to describe a form of general purpose serial computer interface standard; the Universal Serial Bus.

Related Topics

AES

S-PDIF

Digital interconnect

PCM

Basics

The USB standard was conceived as a low-cost multipurpose solution for connecting computer peripheral devices such as the keyboard and mouse. Other applications include connections for printers, external hard drives, digital cameras, network adapters, and digital audio devices. Click here for more detailed information on USB

Audio Applications of USB

General

Lavry USB audio connections receive and transmit PCM digital audio signals. When the computer plays back a digital audio file in a different format, it is converted to PCM format prior to USB output. One example would be the playback of MP3 files in a media player, or in iTunes. In most cases, audio input devices are shown as a “microphone” in the operating system control panels, regardless of whether they are indeed a microphone or line level audio device. In a similar manner, audio output devices are shown as a “speaker” in the operating system control panels, regardless of whether they are a speaker or line level audio device.

Lavry

All current Lavry products with USB connectivity utilize the “Native” USB audio drivers of the computer’s Operating System (OS). This effectively makes Lavry converters “plug & play” with some settings required for optimum results. Please refer to the product manual, information documents listed under the Downloads tab of the product page on the Lavry website, and the product page of the Lavry Wiki for specific information on USB connection and settings.

The Lavry AD11 and DA11 are USB 1.1 compatible.

USB Standards and Audio Specifications

The USB 1.0 Class 1 standard allows for 24 bits/96 kHz maximum resolution for input and output of digital audio. All operating systems (Win, OSX, and Linux) support USB Audio Class 1 natively, which means you don’t need to install drivers; it is plug& play. All support 2 channel audio with 24 bit words and 96 kHz sample rate. The Lavry AD11 and DA11 are this class of device.

USB 2.0 is downwardly compatible with class 1 and supports 32 bit and all common sample rates > 96 kHz With the data rate of High Speed (40 X Full speed), recording 60 channels using 24 bits at 96 kHz is possible. From mid-2010 on USB audio class 2 drivers are available in OSX 10.6.4 and Linux. Both support sample rates up to 384 kHz.

It is unclear if Microsoft® is going to support USB Audio Class 2. If you have an audio device which supports sample frequencies higher than 96kHz, you probably need a third party USB class 2 driver on Windows®.

USB Setup tips

Any USB audio device which uses the Native OS drivers will require looking at the Operating System’s (OS) SOUND settings to confirm that the device is connected properly and configured properly for audio input or output (I/O). It is important that these OS settings be made before launching any audio software that will use these devices. If changes to the settings are required, they will not take effect while the audio software is open. It is recommended that all audio software be closed prior to making changes to the OS settings.

• In Windows computers, the SOUND control panel is used for this purpose.
• In Apple® Macintosh® computers, the Audio MIDI Setup dialog is used for this purpose. Please note there are also some settings in the SOUND control panel for lesser used functions such as checking the function of the built-in digital audio optical output. Most setting that may need to be changed when working with the audio software are in the Audio MIDI Setup dialog.

The input device (“microphone”) must be selected as the Default Input device for this device to be automatically selected by recording software. The output device (“speaker”) must be selected as the Default Output device for this device to be automatically selected by playback or recording software.

Windows

The SOUND control panel can normally be accessed by right-clicking on the speaker symbol next to the clock on the taskbar and selecting Playback devices or Recording devices.

DA11

There are settings in the SOUND control panel/Playback tab section which affect playback using the Lavry DA11. If the DA11 is powered and the OS is booted when the USB cable is plugged into the computer, the DA11 should appear in the list of devices with a speaker symbol and be titled “Speakers/Lavry DA.” A check mark in a green dot will appear on the corner of the speaker symbol if the DA11 is selected as the default device. A phone receiver symbol will appear in the green dot if it is enabled, but not selected as the default device.

To access the Configure, Set Default, and Properties functions, it is necessary to click on the area of the Lavry DA to select it, which is indicated by the area being highlighted in light blue. By either clicking on the Properties button or double-clicking on the Lavry DA area, the Speaker Properties dialog is opened.

The Speaker Properties dialog has four tabs: General, Level, Enhancements, and Advanced. For optimum results check that the level is set to 100 % (the highest setting). Under the Advanced tab there are settings for the output Sample frequency (SF) and word length. For optimum results, set the SF to match the SF of the file being played and the Wordlength to 24 bit; even when playing back 16 bit files! The audio software will introduce dither when this setting is on 16 bit, which can affect the sound quality. The DA11 will accept the 24 bit output and reproduce it at full resolution as long as this setting is 24 bit.(*)

There are two other settings which can have a profound effect on the operation of the DA11; the Exclusive mode settings. There are two check boxes near the bottom of the Advanced tab for “Allow applications to take exclusive control of this devices” and “Give exclusive mode applications priority.” In the vast majority of cases, it is best to use the DA11 with these boxes checked for the most reliable operation.

Doing so will make it impossible for other applications to output sound through the DA11 at the same time the exclusive mode application is running, which can be desirable for serious listening. However, this can also cause the DA11 to “not work” if a different application that has exclusive mode capability is launched prior to launching the desired audio playback software. As a step in trouble-shooting, if the DA11 setup appears to stop working after otherwise working dependably, you can try changing these settings to see if it makes any difference. If it does, this may indicate another audio application had control of the DA11 when it appeared to “not work.” Be aware that even some web browser audio software can cause this type of conflict.

(*) Some audio recording software has advanced WDM drivers which effectively bypass the Windows mixer and Advanced tab settings. In this case, the sample rate setting as well as the level setting in the SOUND control panel may have no effect on the audio going to the DA11. In these cases, it is not necessary to use ASIO4ALL to get good results. This type of software typically bypasses the SOUND settings for the output side, as well. Other types of drivers such as WASAPI also bypass the Windows audio software and also make it unnecessary to manually change the output sample frequency in the SOUND control panel to achieve bit-accurate playback (the audio data which reaches the DA11 is the same as the audio data in the recorded file).

WASAPI

Some playback software offers the option to use WASAPI drivers. There are a number of advantages to this approach, including automatic setting of the output sample frequency by the playback software. Please see WASAPI for more information.

AD11

There are settings in the SOUND control panel/Recording tab section which affect recording when using the Lavry AD11. If the AD11 is powered and the OS is booted when the USB cable is plugged into the computer, the AD11 should appear in the list of devices with a microphone symbol and be titled “Microphone/Lavry ADC.” A check mark in a green dot will appear on the corner of the microphone symbol if the AD11 is selected as the default device. There is also an input bar meter on the right side of the Lavry ADC section which can be useful in troubleshooting.

To access the Configure, Set Default, and Properties functions, it is necessary to click on the area of the Lavry ADC to select it, which is indicated by the area being highlighted in light blue. By either clicking on the Properties button or double-clicking on the Lavry ADC area, the Microphone Properties dialog is opened.

The Microphone Properties dialog has four tabs: General, Level, Enhancements, and Advanced. For optimum results with Windows OS after XP, it may be(*) necessary to use a program like ASIO4ALL to allow full resolution audio to pass from the AD11 to the recording software. This is because the ability for the OS to recognize a line level USB audio device ended with Windows XP. This results in it being necessary to reduce the Level setting in the in the Level tab to 3 - 4 to avoid clipping full level signals from the AD11, because the OS is expecting a microphone level signal. Attempting to record with the level set to 3 - 4 (or +2.1 to +4.0dB) will result in significant loss in signal quality. Please see the document titled “ASIO4ALL Setup English - Basic, Reaper, SonarX1, WaveLab ” under the AD11 product page Downloads tab for details on setting up ASIO4ALL.

Under the Advanced tab there are settings for the input Sample Frequency (SF) and word length. For optimum results, set the SF to match the SF of the AD11 and the Wordlength to 24 bit. Failure to set the SF in the SOUND control panel may result in either a low quality sample frequency conversion being applied to the incoming digital audio, or an error message from the recording program about a sample frequency mismatch.

There are two other settings which can have a profound effect on the operation of the AD11; the Exclusive mode settings. There are two check boxes near the bottom of the Advanced tab for “Allow applications to take exclusive control of this devices” and “Give exclusive mode applications priority.” In the vast majority of cases, it is best to use the AD11 with these boxes checked for the most reliable operation.

Doing so will make it impossible for other applications to input sound at the same time the exclusive mode application is running, which can be desirable for serious recording. However, this can also cause the AD11 to “not work” if a different application that has exclusive mode capability is launched prior to launching the desired audio recording software. As a step in trouble-shooting, if the AD11 setup appears to stop working after otherwise working dependably, you can try changing these settings to see if it makes any difference. If it does, this may indicate another audio application had control of the AD11 when it appeared to “not work.”

(*) Some audio recording software has advanced WDM drivers which effectively bypass the Windows mixer and Advanced tab settings. In this case, the sample rate setting as well as the level setting in the SOUND control panel may have no effect on the audio from the AD11. In these cases, it is not necessary to use ASIO4ALL to get good results. This type of software typically bypasses the SOUND settings for the output side, as well.

ASIO4ALL

When recording with the Lavry AD11 in a Windows computer using audio software with ASIO capability, we recommend using ASIO4ALL or similar WDM/ASIO software to make the AD11 appear as an ASIO device. Changes to the Windows OS made versions after XP incompatible with high quality line level USB input devices by allowing only microphone level adjustment in the SOUND control panel. In order to achieve full quality, it is necessary to bypass this OS function using a program like ASIO4ALL. The other advantage is the ability to make “composite audio devices” which appear to the recording software as a single ASIO device.

• If the recording software has advanced WDM drivers which bypass the Windows SOUND settings, using ASIO4ALL is not necessary to achieve high quality results.

Apple OS

The Audio MIDI Setup dialog has a provision to create an Aggregate Device to combine input and output devices with different physical connections. By doing so, these separate devices appear to the recording software as a single audio interface.

• For basic playback, it is not necessary to create an aggregate device.
• To record with the AD11 and DA11, an aggregate device must be created. Programs like Protools may create their own aggregate device, which is require for use in place of a Core Audio aggregate device. Even if you are using only the AD11 connected via USB, an aggregate device would need to be created with the AD11 for input and the computer’s built-in audio as an output. Please note that the Protools aggregate device does not allow the AD11 and DA11 to be connected via USB simultaneously. The DA11 would need to be connected using he Macintosh’s built-in optical output, which can be combined with the USB connected AD11 in the Protools aggregate device.

For details on settings, please see the document “Connecting to ProTools 9 or 10 (PDF)” which is available under the AD11 product page Downloads tab for details on Audio MIDI settings, or or click here.

Known Issues

Output Sample Frequency Settings

Both Windows and Apple audio require manually setting the output sample Frequency (SF) when used with basic plug & play audio software. This is to allow support of multiple software playback sources with different SF’s to play out through the “speakers” simultaneously. One example is a system sound indicating an error message occurring when using both a word processor and an audio playback program. The system sound may be at 32kHz and the music file at 96kHz, so the OS will automatically introduce sample frequency conversion (SFC) on the source(s) which do not match the output SF setting in the SOUND control panel. Some recording programs effectively bypass the Windows or Apple sound settings and make it unnecessary to manually set them in the SOUND control panel to achieve good results. Other programs have advanced drivers such as WASAPI for Windows, or custom Core Audio drivers for Apple OS which also bypass these settings. Although the Windows SFC is reasonably good quality, most discriminating listeners will prefer to listen to playback at the same SF the file was recorded (no SFC). Most feel the Apple OS SFC is not “high fidelity” and are not happy with the results unless the output SF is set manually or the playback software has advanced drivers to bypass this function.

Drivers

The Lavry AD11 and DA11 utilize the OS native drivers, so there is no driver software to install. In some instances, other USB audio interfaces may use their own USB driver software. It is possible that installing third party drivers may overwrite OS driver or audio software. If you have checked that all settings appear to be correct, have previously installed USB audio software from a company other than Lavry, Microsoft, or Apple, and cannot achieve reliable operation; it is possible that the OS USB software has been replaced or corrupted by the installation of the third party software. If this occurs, try uninstalling any third party software and unplug the Lavry device connected via USB. With the Lavry device powered and the OS booted, re-connect the USB cable from the Lavry device. Go to the OS SOUND control dialog and confirm that the Lavry device appears as an input or output device and that it is selected as the default I/O device before launching any audio software.

Physical Connection

In some instances certain USB ports on a single computer may allow more reliable operation than other USB ports on the same computer. If you experience problems with the audio, try using a different USB port. With the Lavry device powered and the OS booted, re-connect the USB cable from the Lavry device.

Seeing USB Devices on a Windows Computer

Windows computers have a control panel named Device Manager, which can be accessed through the link to the Control Panels or by right-clicking on the Computer link in the Start menu and selecting Properties. Using the right-click method will open the System control panel and on the left side there is a link for Device Manager. The first step is to change the View setting to “Device by Connection.”

You can then expand the tree in the USB section to show all connected devices by clicking on any triangular arrow symbols next to the USB Controllers. In this illustration, the Lavry DA is connected to a USB port which is not used by any other devices. This is the ideal scenario, but in some cases it may not be possible. Try to avoid connection to a USB port shared by other high bandwidth or high priority devices such as wireless mouse/keyboards or WiFi connections.

Seeing USB Devices on an Apple Macintosh Computer

Depending on the OS version, Apple Macintosh computers have a dialog named System Information or System Profiler, which can be accessed through the Finder by searching for it by name or by selecting Utilities from the FINDER/GO menu.

By selecting USB from the Contents column of the System Information or System Profiler dialog, the USB connections are displayed. In this illustration, the Lavry DA is connected to a USB port which is not used by any other devices. This is the ideal scenario, but in some cases it may not be possible. Try to avoid connection to a USB port shared by other high bandwidth or high priority devices such as wireless mouse/keyboards or WiFi connections.

Multiple USB connections

If you want to connect the AD11 and DA11 to the same computer using USB, be aware that this may not work with all computers. If you get a warning regarding bandwidth limitations, or simply cannot get audio into and out of the computer via the Lavry devices, try changing one of the USB connections to a different port. For example, instead of using two front panel USB ports, try using one front and one rear panel ports.

Lavry recommends using an alternative means for connection of the DA11 when the AD11 is connected via USB whenever possible. For example, most Macintosh computers have an optical digital audio output built into the headphone jack. Many PC’s have SPDIF optical or coaxial connections available through the on-board sound. Please note that the output SOUND control panel settings for output SF and Wordlength typically affect on-board sound SPDIF connections in a manner similar to USB. ProTools Macintosh users will need to use this approach because the ProTools aggregate device does not support connection of both the AD11 and DA11 simultaneously.

Changes to the OS

OS manufacturers periodically update or release new versions of their software, which can result in changes to the operation of the USB audio. Because the AD11 and DA11 are Class 1 Compliant audio devices, changes to the OS normally do not affect them in the manner third party drivers are affected.

However, it is possible that third party drivers which are installed when the update happens could be affected and this could in turn affect the operation of the Lavry unit if these drivers replaced the original OS USB audio drivers.