1 PC Audio

2 Sound Card  An expansion board that enables a computer to receive, manipulate and output sounds

3 Sound Card Components  A typical sound card may include:  A/D and D/A converters  Hardware and software to permit recording and playback of 16-bit audio at multiple sampling rates  Software controlled audio mixer  Digital I/O  CD Analogue Audio input  On-board power amplifiers  Analogue line in/out jacks, microphone input, joystick/MIDI connector  FM synthesiser  Wavetable synthesiser

4 Sound Card PCI connector A/D and D/A converters DSP SPDIFF Digital output CD SPDIFF digital input Digital I/O (audio extension connector) CD Analogue Audio input Wave table and FM Synthesizer SPDIFF Digital output Line in jack Microphone jack Line out jack Joystick/MIDI connector Power amp

5 PC Busses and Interfaces  Sound cards are usually connected to the processor via either:  Industry Standard Architecture (ISA)bus 11 Mbyte/sec  Peripheral Component Interconnect (PCI) bus 132 Mbyte/sec Efficiently integrates the computer’s processor and memory with peripherals Has replaced the ISA bus on most modern PCs

6 PC Busses and Interfaces

7  CD-ROM is connected to the processor via IDE or EIDE (Enhanced Integrated Drive Electronics) bus  Burst speeds up to 16Mbytes/second

8 Digital I/O  Some cards provide a direct digital output using an optical or coaxial S/PDIFF (Sony/Philips Digital Interchange Format) connection  For connecting to other digital devices:  Input from CD/DVD-ROM drive  In/Out to DAT and MiniDisc recorders  Output to digital speakers

9 CD Analogue Audio Input  Connects from the analogue audio output on the CD or DVD-ROM drive using a CD audio cable  Provides similar analogue line audio signal as that output from the headphone socket

10 Digital Audio Extraction  DAE also known as “ripping” is the process of moving a Red Book track on a CD, usually music, to a hard drive or other storage medium  In theory DAE enables you to extract digital audio via your EIDE interface from a CD at the speed of your CD-ROM drive  In reality this can be problematic

11 Digital Audio Extraction  Redbook audio format supposes that data will be read in a continuous spiral  Thus there is no addressing provision  Data written onto a CD-ROM must be read continuously with no stops  CD audio data is stored as frames  There is no unique identifier for each frame  Approximate positioning is provided by the frame subcode over 98 frames, 1/75 th second

12 Digital Audio Extraction  In DAE large data files are moved from the CD-ROM drive to the hard disk  This can not happen continuously  Intermediate buffers are filled and emptied  Thus, CD-ROM drive will read sectors in short bursts  As positioning is not exact, small clicks and pops may appear in the music  Special software/ hardware is required to overcome these synchronisation errors

13 Line In/Out  Standard type of audio signal to minimise noise and distortion when:  processing sound  transferring it from one component to another  reproducing recorded sound  1v peak to peak  Not really enough to drive non amplified speakers  But larger than the mic input

14 Synthesis  There are two main techniques for creating sounds in music synthesisers  Frequency Modulation (FM) synthesis - uses one periodic signal (the modulator) to modulate the frequency of another signal (the carrier)  Wavetable synthesis – uses short samples from the original instrument

15 FM Synthesis  Each FM voice requires a minimum of two signal generators  Sophisticated FM systems may use 4 or 6 operators per voice

16 Wavetable synthesis  Stores high quality sound samples digitally, and then replays these sounds on demand  For many instrument sounds, the sound can be modelled as consisting of two major sections:  attack  sustain

17 Windows Multimedia API  Allows access to the sound card functionality  But is limited to the access functions that windows provides  No direct means of mixing  DirectX API  Provides real-time low level access to sound card Functions for mixing, controlling volume, balance etc.

18 Universal Serial Bus  USB provides fast, user friendly I/O device connection  12 Mbps (slow but faster than the serial ports)  Sufficient for applications using: S/PDIF MPEG-1 and some MPEG-2  Future versions 120 – 240Mbps

19 Digital Speakers  Connect to USB  Contain:  D/A converter  Amplifier  Less susceptible to interference  Max run of a USB cable is 5 M

20 Fin