On Friday 10 September 2004 Martijn Sipkema wrote: I don't agree on the subject that USB bulk transfers cause bad MIDI timing. Of course, you can't use the same USB host controller at a time with a MIDI interface and some other device like a CD writer and expect both good MIDI timing and fast CD burning. If you can reserve a host controller exclusively for your USB MIDI device, you will get pretty good results, most of the time. There are four USB data flow types, Control transfers and: - Bulk transfers are used to request or send reliable data packets up to the full bus bandwidth. Devices like scanners or scsi adapters use this transfer type. - Interrupt transfers are similar to bulk transfers which are polled periodically. If an interrupt transfer was submitted the host controller driver will automatically repeat this request in a specified interval (1ms - 255ms). - Isochronous transfers send or receive data streams in realtime with guaranteed bus bandwidth but without any reliability. In general these transfer types are used for audio and video devices. (quoted from http://wwwbode.cs.tum.edu/Par/arch/usb/usbdoc/node8.html) MIDI streams need to be reliable (a single byte lost isn't acceptable), so Isochronous is not an option. Interrupt or Bulk transfers are very similar: they use only the available bandwidth at each moment, so there can be unwanted delays and timing problems. Some manufacturers' proprietary protocols include a timestamp with each USB MIDI packet to enhance the time accuracy, but this can be done either in bulk or interrupt transfers. Regards, Pedro