With an audio adapter, a PC can record waveform audio. Waveform audio (also known as sampled or digitized sound) uses the PC as a recording device (like a tape recorder). Small computer chips built into the adapter, called analog-to-digital converters (ADCs), convert analog sound waves into digital bits that the computer can understand. Likewise, digital-to-analog converters (DACs) convert the recorded sounds to an audible analog format.
Sampling is the process of turning the original analog sound waves into digital (binary) signals that the computer can save and later replay (see Figure 16.7). The system samples the sound by taking snapshots of its frequency and amplitude at regular intervals. For example, at time X the sound might be measured with an amplitude of Y. The higher (or more frequent) the sample rate, the more accurately the digital sound replicates its real-life source and the larger the amount of disk space needed to store it.
Figure 16.7Sampling turns a changing sound wave into measurable digital values.
Originally, sound cards used 8-bit digital sampling that provided for only 256 values (28), which could be used to convert a sound. More recently, sound cards have increased the quality of digitized sound by using 16-bit (216) sampling to produce 65,536 distinct values. Today's highest-quality sound cards feature 24-bit sampling (224), which translates into more than 16.8 million possible digital values that can be matched to a given sound.
Note - For more information on the differences between 8-bit and 16-bit audio sampling, see "8-Bit Versus 16-Bit," in Chapter 16 of Upgrading and Repairing PCs, 13th Edition, included on the disc accompanying this book.
You can experiment with the effects of various sampling rates (and compression technologies) by recording sound with the Windows Sound Recorder or a third-party application set to CD-quality sound. Save the sound and play it back at that highest-quality setting. Then convert the file to a lower-quality setting, and save the sound file again with a different name. Play back the various versions, and determine the lowest quality (and smallest file size) you can use without serious degradation to sound quality.
Who's Who in Audio
Because audio adapters have become common features in systems, many vendors have produced audio adapters, audio chips, integrated motherboard chipsets with audio features, and even specialized vacuum tube audio. This section examines some of these companies and their products.
As you've learned in other chapters, I believe it is very important to get all the technical information you can about your computer and its components. By knowing who makes the audio chip your computer depends on, you can find out what the hardware can do and be better able to find upgrades to the software drivers you need to get the most out of your audio hardware.
Chipset Makers Who Make Their Own Audio Adapters
Just as graphics card vendors are divided into two camps, chipset makers are divided into these two categories:
Card and device makers who produce their own chipsets
Card and device makers who use chipsets from other vendors
Audio adapter vendors fall into the same categories. One of the pioneers of the audio adapter business, Creative Labs, has also been among the leaders in developing audio chips. Creative Labs develops audio chips primarily for its own Sound Blaster–branded products, but it has sold some of its older Sound Blaster 16 products into OEM markets.
Creative's major audio chips have included the following:
Vibra-16. This was used in the later Sound Blaster 16 cards; it doesn't support wavetable or 3D effects.
Ensoniq ES137x series (ES1370/71/73). These were used in the Sound Blaster PCI64 and PCI 128 series as well as the Ensoniq Audio PCI and Vibra PCI series. They support soft wavetable features, four speakers on some models and Microsoft Direct 3D but don't support 3D acceleration or EAX positional audio.
EMU-8000. This audio chip was used by the AWE32/64 series and features 32-voice wavetable synthesis but no 3D acceleration. The AWE64 used software to generate 32 additional voices for a total of 64 voices.
EMU10K1. This audio chip was at the heart of the Live! and Live 5.1 series sound cards as well as the PCI 512; it features 3D acceleration, EAX positional audio for one audio stream, a reprogrammable DSP, and soft wavetable support.
EMU10K2 (also known as Audigy). This is the audio chip at the heart of Creative Labs' Sound Blaster Audigy series sound cards; it features 3D acceleration, EAX HD positional audio for up to four audio streams, a reprogrammable DSP, and soft wavetable support. This chip supports professional-level 24-bit sampling at 96KHz and real-time sampling at Dolby Digital–quality 24-bit samples at 48KHz.
CA0102 (also known as Audigy 2). This audio chip is the one used by the Creative Labs Audigy 2 series. It's a development of the EMU10K2 chip, adding support for 24-bit 96KHz output, Dolby Digital EX 6.1 decoding and 6.1 sound in DirectX games, and 64 hardware polyphonic voices.
CA0185. This audio chip is used by the Sound Blaster MP3+. It features 2.1 audio support for analog and digital speakers, 48KHz/16-bit playback and recording, and 3D acceleration.
CA0186. This audio chip is used by the Audigy 2 NX. It features Dolby Digital EX 7.1 decoding, 7.1 sound in DirectX games, 96KHz/24-bit stereo output, and 3D audio acceleration.
CA0102-ICT (also known as Audigy 2 ZS). This audio chip is used by the Creative Labs Audigy 2 ZS series. It's a development of the CA0102 chip, adding support for Dolby Digital EX 7.1 decoding, Dolby ETS decoding, 7.1 sound in DirectX games, and 192KHz/24-bit stereo output.
Various other companies have produced their own sound chips in the past but no longer do so. The primary makers that fit in this category are
Aureal. Its A3D technology was regarded by many as superior to Creative Labs' original EAX 3D positional audio, but the company was absorbed by Creative Labs in mid-2000. Because Creative's new EAX HD is superior to A3D, there will be no further development of this technology.
Yamaha. Its OPL2 and OPL3 chips were among the best FM-synthesis chips used on older sound cards, and its MIDI performance in later models was outstanding. However, its emphasis is now on MIDI daughtercards and professional sound-recording cards such as the SW1000XG. Some of its retail and OEM products might still be available, though. Yamaha maintains drivers and support links for its branded and some OEM cards at http://www.yamaha.co.jp/english/lsi/us.
Philips. ItsIts ThunderBird Q3D (SAA7780) and ThunderBird Avenger (SAA7785) chips, jointly developed with QSound Labs, provided high-quality 3D acceleration for Philips's now-discontinued line of PCI-based sound cards. Some third-party sound cards also used the SAA7780 chip, but the six-channel SAA7785 was used only by Philips. See Table 16.4 for details.
Should you panic if your favorite audio adapter is an "orphan?" Not necessarily. If the audio adapter vendor provides good technical support and up-to-date drivers, you're okay for now. But, the next time an operating system update or new audio API shows up, you probably won't be able to take advantage of it unless you replace your audio adapter.
This chapter is from Upgrading and Repairing PCs, 16th edition,by Scott Mueller. (Que Books, 2004, ISBN: 0789731738). Check it out at your favorite bookstore today.
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