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1 PC Audio
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2 Sound Card An expansion board that enables a computer to receive, manipulate and output sounds
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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
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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
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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
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6 PC Busses and Interfaces
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7 CD-ROM is connected to the processor via IDE or EIDE (Enhanced Integrated Drive Electronics) bus Burst speeds up to 16Mbytes/second
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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
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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
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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
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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
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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
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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
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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
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15 FM Synthesis Each FM voice requires a minimum of two signal generators Sophisticated FM systems may use 4 or 6 operators per voice
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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
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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.
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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
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19 Digital Speakers Connect to USB Contain: D/A converter Amplifier Less susceptible to interference Max run of a USB cable is 5 M
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20 Fin
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