USB Audio

[Billaboard]

Please bear with me and/or ignore this long message, but any help with what I should try or learn next would be much appreciated.

Below I have copied a message I sent to another forum and which had no response. I am now at the stage where I think I will have to try to learn or refresh my out of date knowledge. I am starting to refresh my C++ in the hope that I can write a simple program to address audio interfaces, and then use debugging to try to trace where the problems appear, alternatively, it has been suggested that I read up on Interprocess Communications to see if that leads me anywhere. I'm ashamed to admit that I have a copy of USB Complete somewhere, but haven't been able to locate it and am not sure this is a specific USB problem. Here's the post.....

 

Can anyone help with this? I have asked all over the place, but the only suggestion from Microsoft diagnostic forums is that it might be a Win 7 versus chipset clash.

I have an Acer 5536G AMD Turion X2 based laptop. I'm retired, but my work still continues as a hobby with pro and semi-pro audio. I advise and work with broadcasters. I need to find out why things happen so that I can advise other users, mainly about equipment purchase.

Most pro audio interfaces use asio drivers which bypass most of the Windows sound system. The drivers also provide WDM drivers which are seen by Windows. All drivers referred to here are up to date and the correct driver for the circumstances.

The Acer runs fine with certain standard provisos (** see below) when I use a USB2.0 audio interface. If I use a usb 1.1 interface (eg M-Audio Fast Track usb or Edirol UA-3FX), the audio is unusable with either massive crackles or juddery breakup of the sound. If I introduce a usb2 hub (which changes the usb steering in the machine), the sound becomes good.

Without the hub, if I open Control Panel, Sounds and select the recording tab, the sound becomes good. Switching between the Playback (or any other) and Recording tabs switches playback bad and good. This is totally repeatable.

I have used various diagnostics, and have ended up with xperf and NetMon which confirm that the usb data is consistent and good when the audio is good, but is interrupted by SELECT_INTERFACE and CONTROL_TRANSFER messages when the audio is bad.

This happens on Windows 7 32 and 64-bit. It doesn't happen on a Lenovo Intel-based machine. It also doesn't happen on the Acer when it runs Vista 32-bit.

Can anyone suggest where to go from here?

** The proviso is that DPC Latency seems to be a problem on many current laptops running Win 7, and this causes occasional glitches when wifi is running**

[Jan Axelson]

Always use a hub.

With a full-speed device, the hub uses high speed upstream (toward the host) and full speed downstream (toward the device). The result is that the hub requires less bandwidth at the host than if the device attached directly to the host's root port.

Select_Interface suggests that the host may be requesting the device to use an interface that uses less bandwidth, and if so, that would affect performance.

If you are using multiple audio devices at once, give each one its own hub or use a hub with multiple transaction translators.

Jan

[Billaboard]

Using a USB2 hub certainly cures the problem here. It is interesting that this is contrary to the most common advice in audio forums, which is usually to remove any hubs.

I have now located my 3rd Edition of USB Complete. "She" had tidied it to amongst her poetry books. I am now trying to skim read alongside my trace of the data transition from working to not working. I obtained the trace using Microsoft Network Monitor 3.4 to show the results of a usbport trace via Logman. I don't feel that I have a grasp of this yet - for example is the Select_interface that the Microsoft software shows the same as set_interface, and are both these commands likely to switch the usb interface between the two driver modes, asio and wdm?

I am still not clear why switching between tabs in Windows Control Panel causes a bunch of failures in the complete_isoch_transfer commands followed by the select_interface command. I cannot detect any change in the audio from either the on-board Realtek audio or from the Edirol interface when I switch tabs except when the particular fault is set up. And it doesn't happen on the same machine running Vista.

I am really grateful for the reply and apologise for my lack of understanding.

[Jan Axelson]

is the Select_interface that the Microsoft software shows the same as set_interface, and are both these commands likely to switch the usb interface between the two driver modes, asio and wdm?

I don't know for sure if they refer to the same thing. An analyzer that decodes control requests will show the requests to the device so you can confirm whether the host sent the request.
 

I am still not clear why switching between tabs in Windows Control Panel causes a bunch of failures in the complete_isoch_transfer commands followed by the select_interface command.

I can't explain it either.

If you want to track down exactly what is happening, recording the USB traffic is the place to start. If the problem is within Windows, there may be no solution other than working around the problem by using a hub.

Jan

[Billaboard]

Many thanks. I will continue to investigate, read and try to understand!