USB AUDIO CARD
This document describes a USB AUDIO CARD. Features of this device, hardware
architectures, software techniques and skills, theory of USB audio device, structure of
USB audio driver in Windows system, and some future proposals and introduced and
discussed in this document. Some photos and charts are also listed in the appendix
section.
Introduction
Several years ago I have used 51 series microprocessor such as at89c2051, at89c51 from ATMEL
in my project, these MCU are very economic and easy to use. So far they are still running in many
fields. Last year because of the need of a new project, I employ an AVR microprocessor
At90s8515 from ATMEL, it’s high speed and ISP feature help me finish my project quickly.
When I read the introduction of Atmega162L microprocessor, I was deeply attracted by it’s
powerful features. Here I have to thank this contest giving me a chance to realize the Atmega
series microprocessor.
Now many kinds of USB peripheral devices appear in our life. Such as USB keyboard, USB
mouse, USB camera and U-disk are very familiar besides your computer. It is obvious that USB
interface is very much more convenient than any other interface s such as PS/2, PCI and IDE.
Atmega162 has 16Kbytes flash and 1Kbytes ram, especially 16MIPS throughput at 16MHZ.It is
enough to finish a USB AUDIO CARD. As we know, many audio cards in our computer belong to
PCI device, because of the high throughput of PCI interface, many devices select PCI. But now
USB2.0 has also high speed to 400Mbps. In fact, the data rate of raw real time stereo audio is very
slow, if your sample rate is 48KHz, and one sample has 16bits, the bit rate is only
48Khz*16bits=768Kbps.Do you remember ISA audio card in intel486 computer before? So I
select USB1.1 interface chip, which is USB full speed transceiver.
My plan is to design an audio card to play all formats audio data, but because the limit of buffer in
the USB transceiver, the highest sample rate in my card has to be 44.1KHz. If you want to let it
support 48Khz, you can select another USB transceiver whose ISO buffer is bigger than 128
bytes.
With a USB B-type to A-type cable, my audio card can be easily connected with
computer. After a few minutes, Windows system will tell you a new composite USB
device is found, and then audio device driver is installed automatically. In the device
manager, a USB Audio device appears. After you select the USB audio device as
preferred audio device, windows system will transfer audio data to this card. After
connecting earphone with this card, you can hear voice when you play a MP3 or WAV
file.
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