Sound Cards

1
Sound Cards

• Karl Heinz Kurze

2
Sound Cards have a minimum of four functions.
These functions are

• Synthesizer
• MIDI interface
• Analog-to-digital conversion during the recording
  (A/D).
• Digital-to-analog conversion during the playback
  (D/A).

3
The Synthesizer

• The synthesizer delivers the sound. That is, the
  sound card generates the sounds. Here we have
  three systems
• FM synthesis, Frequency Modulation
• Wave table
• Physical-modeling

4
FM synthesis

• The oldest of these methods is called FM
  synthesis. FM synthesis does not produce high
  quality reproductions of the instruments they are
  supposed to be. How it works is this the sound
  card is equipped with a synthesizer chip. This
  chip produces sine waves which are the beginning
  of sound. By combining several different sine
  waves, the chip is able to create complex
  waveforms, and these waveforms are supposed to be
  as close as possible to the actual sound of the
  instrument. In reality, though, the sound is
  "canned". FM synthesis cards are older cards, and
  are not much used today.

5
Wave tables - sampling

• Most boards sold today use what is called
  wavetable synthesis. What this means is that in
  the on-board ROM is stored actual recordings of
  the instruments. These recordings are then used,
  by changing the pitch of and blending, to create
  much more life-like sound reproductions. Such
  sound cards must have ample memory on board to
  store the sounds. Many sound cards are expandable
  so that you can add memory and create your own
  wavetable recordings. The quality of the
  wavetable synthesis is a function of the quality
  of the recordings. Short, low-resolution sound
  tables produce cheap sounds.

6
Physical-modeling synthesis

• The third method of sound reproduction is called
  physical-modeling synthesis. In short, a card
  using this method would emulate the vibrating
  sound system of an instrument (such as a guitar
  string) by creating a similar model through
  software. The sound chip would create wave
  vibrations that would act like a physical wave.
  This method of sound creation is incredibly
  life-like and is thus increasing in popularity.
  It is usually found on higher end sound cards.
  Creative Labs was one of the first to implement
  the method. The Creative Labs AWE64 Gold has 14
  instruments re-created through this method.

7
Analog-to-digital conversion (ADC)

• When a sound card records analogue audio, it is
  converting the sound waveform into digital
  information and then copying this in real time
  onto the hard disk. Essentially, it is using the
  disk as a digital tapeless recorder. The process
  of converting analogue to digital is known as
  digitising or sampling. With audio, the analogue
  waveform is chopped into a number of slices per
  second. At each slice, the amplitude is measured
  and rounded to the nearest available value.
  Clearly the more chops per second (sampling rate)
  and the finer the values assignable to the
  amplitude (dynamic range), the better the
  representation of the original.

8
Digital-to-Analog conversion (DAC)

• During DAC, digital information stored in the
  hard disk is sent back to the sound card where it
  is then converted back into its analog form by
  the synthesizer.

9
From ISA to PCI

• ISA bus bandwidth is rather limited (8 Mbps). A
  stereo-CD data stream can be 1.4 Mbps, a large
  demand for the ISA bus. The PCI bus, on the other
  hand, offers a 100-MBps bandwidth or higher.
  Several simultaneous sound channels are no
  problem for the PCI bus.
• There are other benefits to PCI. The PCI bus
  allows cooperative signal processing, which means
  that tasks can be shared between the main system
  processor and a separate audio processor on the
  sound card. This means that the audio signals are
  free of interference from other tasks thereby
  making it 10 20 times more efficient than ISA
  based sound cards.
• One pitfall of the PCI bus arises out of older
  DOS applications. Legacy DOS applications are
  designed so that they require a DMA and IRQ to
  move audio data from the main system memory. This
  means they use Sound Blaster compatible
  protocols. These are only features of the ISA
  bus, not PCI. For this reason, there is a risk
  that older DOS games will not run with PCI sound
  cards. There are workarounds for this ISA-PCI
  problem in DOS. Using special hardware, it is
  possible to redirect the PCI interrupts into the
  legacy space, in effect making them ISA IRQ's.
  The DMA requirement for DOS is being handled by
  enhancements to the PCI bus protocol. The total
  effect is to provide DOS support for PCI sound
  cards.

10
DirectX

• DirectX was written by Microsoft to allow
  low-level control of the hardware and allow high
  performance multimedia within Windows instead of
  DOS. DirectX 5.0, for example, allows low-level
  control of audio files, giving the ability to mix
  multiple .WAV files, as well as control the
  balance, volume, and playback rate of each.
  DirectX API's are divided into sections, each
  section controls a different function. We have
  DirectDraw, DirectSound, DirectSound3D,
  DirectPlay, etc. DirectSound is what allows the
  low-level control of the sound equipment in the
  PC. DirectSound3D allows 3-D sound capabilities
  from only two speakers, giving rise to positional
  audio. Positional audio manipulates the
  characteristics of sounds to make them seem to
  come from a specific direction, such as from
  behind or from far to the left. In version 7.0
  you find improved 3D acceleration of sound as
  well as picture with reduced CPU usage. The
  performance should be increased with 20 compared
  to version 6.1.

11
Environment Simulation

• DS3D may have supported positional audio, but it
  didn't offer much support for adding reverb, let
  alone considering individual reflections, to
  simulate different environments. Fortunately DS3D
  does support extensions to the API, and this need
  was soon met by a couple of new sound standards
  which have gained widespread support from games
  developers Aureal's A3D technology and Creative
  Technology's Environmental Audio Extensions (EAX).

12
Reverb

• Sound that is heard is a mixture of direct path
  sound and reflected sound. Reflected sound might
  reach our ears after bouncing off a wall or
  object, and the material of these obstacles
  absorbs certain frequencies, along with reducing
  the overall volume. This "first-order reflection"
  arrives not only sounding different from the
  direct source, but also slightly after it.
  Second-order reflections and so on take this
  effect further still. The quality and delay of
  the reflected sound reveals a great deal about
  the surrounding environment and its size.
• Most humans can perceive precisely where
  first-order reflections are coming from, and some
  can distinguish second-order reflections too.
  However, as more and more reflections arrive at
  the ear, the brain tends to combine them into one
  late-order reflection echoing effect known as
  reverb. Using reverb properly is the first key to
  simulating different environments.

13
Aureal A3D

• Originally developed in 1997 in collaboration
  NASA (National Aeronautics and Space
  Administration) for use in flight simulators,
  Aureal's A3D technology has subsequently
  progressed through a number of versions.
• ASD1 improved upon DS3D by providing hardware
  acceleration, a more advanced distance model
  allowing simulation of different atmospheric
  environments, such as thick fog or underwater and
  a resource manager that allows developers to take
  advantage of the number of 3D streams the sound
  card can handle and control use of Aureal's 3D
  sound algorithms.
• The A3D2 version actually takes the geometry
  information of the room that is fed to the
  graphics card, and uses it to render realistic
  sonic reflections and occlusions. Using a
  technology called WaveTracing, A3D2 genuinely
  calculates up to 60 first-order reflections,
  which interact in real time with the environment,
  and then groups later-order reflections into
  overall reverb.

14
Aureal A3D

• ASD3 takes the technology to the next level by
  adding a number of new features
• Volumetric Sound Sources When developers define
  an audio file to a sound source, the sound source
  must have a location so that it can be rendered
  in relation to the listener. This is usually done
  via a point source the point where the source
  is. However, some sources will not "reside" in a
  single point flowing water, wind, crowd cheers,
  etc. will actually stretch out or extend in
  various areas. To more accurately model these
  sources, ASD3 allows them to be defined as
  volumetric sound sources, thereby positioning
  them better.
• MP3 playback Previously, audio streams for 3D
  audio have had to be WAV files. Now, MP3 files
  can be used, thereby both reducing their
  associated storage space and increasing their
  quality.
• Reverb The sum of all late order reflections.
  Aureal's geometric reverb will work on Vortex2
  (and later) cards, as well as automatically
  translating to EAX or I3DL2 if a sound card does
  not have the appropriate A3D support.
• Streaming Audio Automatic support for streaming
  audio has been added, eliminating the complex
  layer of development normally required for
  client/server interactive entertainment
  applications that use existing audio solutions.
• A3D2 was such a computationally complex system
  that Aureal developed a processor dedicated to
  the necessary number crunching. A3D3 requires
  even greater processing power, which is provided
  in the shape of an additional DSP to accelerate
  the new commands.

15
Creative Technology's Environmental Audio
Extensions EAX

• EAX 1.0 was designed to provide developers with
  the ability to create a convincing sense of
  environment in entertainment titles and a
  realistic sense of distance between the player
  and audio events. The approach Creative took to
  achieve this was, computationally, significantly
  easier than the one Aureal had taken with A3D.
• EAX 2.0 enabled the creation of more compelling
  and realistic environments with tools that allow
  the simulation of the muffling effects of
  partitions between environments (such as walls)
  and obstacles within environments (such as
  furniture).
• EAX 3.0 introduced the ability to "morph" between
  environments.

16
Creative Technology's Environmental Audio
Extensions EAX

• In late-2000 a number of EAX effects were
  incorporated into the DirectX Audio component -
  the functions of which were previously shared
  between the DirectSound and DirectMusic
  components - of the latest release of Microsoft's
  suite of multimedia APIs, DirectX 8.0. A few
  months later, Creative unveiled an API platform
  for games developers wanting to incorporate Dolby
  Digital content into their games. Earlier
  soundcards had allowed Dolby Digital to be passed
  directly through the card and decoded by an
  external decoder. However, with the "5.1" version
  of its successful SoundBlaster Live! sound card
  Creative supported decoding directly through one
  of their audio products for the first time, the
  card being able to output straight to six
  discrete analogue channels (5 speakers 1
  sub-woofer).