1 / 38

Graphics 2 & Sound

Graphics 2 & Sound The First Rule of Computer Graphics is: Compress Last Take a picture or scan an image at the highest possible resolution. Work on that image at that resolution. Save the image in its original and compressed formats.

issac
Télécharger la présentation

Graphics 2 & Sound

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript

  1. Graphics 2 & Sound CSE5900 -- Intro to MM Computing -- Lecture 3

  2. The First Rule of Computer Graphics is: • Compress Last • Take a picture or scan an image at the highest possible resolution. • Work on that image at that resolution. • Save the image in its original and compressed formats. • Contemporary scanners = 1,200 x 1,200 dots per inch; 32 bit (4 byte) colour, so we have • 1200 * 1200 *4 * (say) 7 * 5 = 201,000,000 bytes • Hummm. We’re going to need LOTS of RAM. (And hard disk space) • (This is why digital cameras are still ‘low resolution’, even with, say, 4,000,000 pixels per image.) CSE5900 -- Intro to MM Computing -- Lecture 3

  3. Oh, Dear • If we are working with 200mb files, we have the following problems. • We can’t actually see the detail without zooming in a lot. • It will take a fair amount of time to get information on to and off of the hard disk. • It will take time to get the image to and from: • Disk and RAM (video RAM or standard RAM) • RAM and CPU • CPU to video card • Video card to monitor • Much of the contemporary evolution in computing tries to improve the bandwidth of these connections CSE5900 -- Intro to MM Computing -- Lecture 3

  4. Crucial Definitions • Bandwidth • The rate at which data moves from point A to point b. The throughput of a connection, measured in either bits or bytes. • Bus • The physical connection(s) between point A and point B • Busses come in two flavours • Serial - one signal wire, so 1 bit at a time. • COM ports • USB (universal serial bus) • Parallel - many signal wires (8, 16, 34 or 64 at present), many bits at the same time. • PCI bus • Northbridge or front end bus CSE5900 -- Intro to MM Computing -- Lecture 3

  5. Busses, Words, and Addresses • We can speak of the capacity of four things in terms of the numbers we are discussing: • Bus capacity, bits or wires • Word length: the number of bits a CPU deals with as a unit. Currently usually 64 bits, and moving towards 128. • Maximum address size: the highest location address (for RAM, hard disk, etc) measured in bits. • Operating system: The size, in bits, of an instruction. Note that the word size has to be a multiple of the instruction size CSE5900 -- Intro to MM Computing -- Lecture 3

  6. In the Beginning (1983) RAM CPU Key- board Floppy Printer Screen CSE5900 -- Intro to MM Computing -- Lecture 3

  7. A Little Later (1985) RAM Video Card Video RAM ALU - Floating point Screen CPU Key- board Floppy Hard Disk CSE5900 -- Intro to MM Computing -- Lecture 3

  8. Another View Mouse Modem Printer LPT2 COM1 Floppy Hard Disk Screen COM2 LPT1 CPU RAM IO Card Video Card Disk Controller Bus CSE5900 -- Intro to MM Computing -- Lecture 3

  9. Windows 2 Arrives (1992) RAM ALU - Floating point CPU Key- board Floppy Video RAM Mouse Hard Disk Video Card Screen CSE5900 -- Intro to MM Computing -- Lecture 3

  10. Yesterday CPU Video RAM Video RAM Video Card Games--3D Video Card Windows--2D Screen CSE5900 -- Intro to MM Computing -- Lecture 3

  11. Today • RAM CPU Video RAM Video Card Windows--2D Games--3D Screen CSE5900 -- Intro to MM Computing -- Lecture 3

  12. Today - A Second Perspective Video RAM Video Card RAM North Bridge CPU Cache Memory South Bridge Disk Controller Sound Card Other PCI Cards CSE5900 -- Intro to MM Computing -- Lecture 3

  13. Tomorrow Video RAM Video Card Rendering Physics, etc. RAM North Bridge Cache Memory CPU Cache Memory CPU South Bridge Disk Controller Sound Card Other PCI Cards CSE5900 -- Intro to MM Computing -- Lecture 3

  14. RAM to Screen Video RAM (Frame Buffer) Screen Pixels • A pixel has a matching chunk of video RAM CSE5900 -- Intro to MM Computing -- Lecture 3

  15. The Conversion Step • But RAM is digital and video is analog, so we need a digital to analog converter (DAC) Video (composite) RAM (rgb) RAM DAC CSE5900 -- Intro to MM Computing -- Lecture 3

  16. Colour Information Storage • 0 to 255 for red 8 bits • 0 to 255 for blue 8 bits • 0 to 255 for green 8 bits • 0 to 255 for Alpha 8 bits • So 32 bits (4 bytes) per pixel • 1,024 x 768 x 4 = 3,145,728 bytes per frame in video memory • So 16mb video memory may be ok, where the image is “pre-cooked” (my jargon) • Assuming there’s enough bandwidth for 24 frames/second CSE5900 -- Intro to MM Computing -- Lecture 3

  17. Pre-Cooked versus Home Cooked • Pre-Cooked • All of the images are prepared in advance, and are on disk or CD-ROM • The processing steps are: • Read from hard disk into CPU • Decompress compressed images • Build the frame in video RAM • Run through RAMDAC onto screen • The limits are: • The bandwidths, especially for video • The file sizes versus storage capacities • The complexity of decompression • Everything has to be completely prepared in advance. It’s all finished art CSE5900 -- Intro to MM Computing -- Lecture 3

  18. Pre-Cooked versus Home Cooked, 2 • Home Cooked • Where you can’t prepare all images in advance • First person perspective games, for example • Player can move in any direction, look up, down and around, explore • The display has to be created on the fly • Curse you, Doom, for starting it all! • Pre-cooked is sometimes called “2D” and home cooked is sometimes called “3D”, which is completely misleading. • The difference is what’s done in advance or in real time • Traditional video cards could do interactive 2D (and pre-cooked 3D) • 3D accelerator cards can do interactive 3D image creation in real time. CSE5900 -- Intro to MM Computing -- Lecture 3

  19. Digression 1: APIs • API = application programmer’s interface • A large set of functions used to extend a standard programming language into a specialized area • These functions can be used on the fly as needed • There are 2 standard 3D graphics APIs • OpenGL (originally from Silicon Graphics, now non-proprietary, used for Doom) • Direct3D (from Microsoft, part of DirectX) • Allow work (by games programmers) at • Low level -- set up scene using graphic primitives • High level -- make small variations to a scene -- think of sprites and larger elements CSE5900 -- Intro to MM Computing -- Lecture 3

  20. Digression 2: Building a 3D Image • We have to come up with a 2D screen rendition of a 3D thing which we’ve built on a 2D screen-based workspace • First comes the wire frame models of the object. This is all that’s really there, and the rest is just processing. • With the pre-cooked, all the processing takes place in advance and the results (not the wire frames) are distributed. • With home cooking, the wire frame models are distributed, together with textures and materials, and the processing takes place in real time in the 3D accelerator usually using a game engine created using a API (Direct3D or OpenGL) CSE5900 -- Intro to MM Computing -- Lecture 3

  21. Digression 2: Building a 3D Image, 2 • There has to be a camera position from which we look at the wire frames. • We have to get rid of things behind other things (clipping) • We have to provide light sources, with colour mixes, intensities and directions, resulting in shadows, reflections, etc. (ray tracing, usually faked in games) • We have to apply different textures (e.g., red gum) to the surfaces of the wire frames (texture mapping) • We have to smooth everything out according to all the above (rendering) • The 3D accelerator cards provide the tools to do this kind of stuff in real time CSE5900 -- Intro to MM Computing -- Lecture 3

  22. How Well Do They Work? • Consider that each frame in an animated film takes a network of computers many minutes to render. • Consider that the wire frames for animated films have hundreds of thousands or millions of polygons (the primitive used for processing) • Consider that the audience for 3D accelerators is 16 year old boys who haven’t graduated from killing things (a low resolution occupation) to sex (a high resolution preoccupation) • The cards are getting good at keeping their intended audience happy • But they are miles from being able to do Riven in real time CSE5900 -- Intro to MM Computing -- Lecture 3

  23. Music Hath Charms to Sooth the Savage Beast Introduction to Sound Processing CSE5900 -- Intro to MM Computing -- Lecture 3

  24. Sound Is Analog • So there’s infinite variation • Like a rock thrown into a pond, there are waves: • Amplitude: how high the waves are -- Loudness • Frequency: how many waves per second -- Pitch • Loudness is measured in decibels • This is a log scale, so 20 is ten times as loud as 10, 30 is ten times as loud as 20, and so forth. • You can distinguish from just over 0 dB to 120dB • 37 quiet office (no air-conditioning) • 59 conversation • 76 loud factory • 110 really loud night club or rave • 140 threshold of pain (well, for some) CSE5900 -- Intro to MM Computing -- Lecture 3

  25. Sound Is Analog, 2 • Pitch is measured in Hz (Hertz, cycles per second) and kHz. • You can distinguish between a few Hz and 15 - 20 khz (this is age dependent) • Lowest note on piano 27 Hz • Highest note on piano 4,186 Hz (4.186 kHz) • Lowest vocal sound 80 Hz • Highest vocal sound 800 Hz • The A above middle C 440 Hz (used to be lower!) • But a sine wave just at these frequencies sounds sterile: it lacks the overtones, the harmonics, produced by all natural sources of sound. Think of the FM synthesis sound of a cheap sound card. CSE5900 -- Intro to MM Computing -- Lecture 3

  26. Sound Is Analog, 3 • An instrument vibrating produces lots of sounds above the fundamental tone. • Many of these are various octaves above the fundamental • Octave = double the frequency • To get realistic sound we have to pick up at least the 4th harmonic, 4x the frequency of the fundamental. • So we have to pick up to 12kHz for, say a realistic flute sound (where the highest fundamental is just under 4kHz • More is better until, say 20kHz where a 5 year old’s hearing cuts out. CSE5900 -- Intro to MM Computing -- Lecture 3

  27. Sound Into Bits (ADC) • Something that always confuses me: • The 16 bits used (0 - 64k) record the amplitude (loudness) • The differences between successive 16 bit samples contain the frequency (pitch) • Remember, a high wave also has a trough between peaks. • So how often do we have to sample to get enough samples • 2x the maximum difference we want to catch. • And we want to catch differences up to 20mHz, so we have to sample at at least 40,000 times a second. • So your CDs contain music sampled at just over 44,000 times a second. • So the digital signal bandwidth must be 16 x 44,000 = 704,000 bits per second or 88 kbps. With stereo sound, we have to have two such samples, so a 1x CD-ROM bus goes at 176 kbps, which we already knew! CSE5900 -- Intro to MM Computing -- Lecture 3

  28. Bits Into Sound (DAC) • Amplifiers and speakers are analog devices, so • The CD player does DAC and passes the results as an analog signal to your stereo system. • It does the same if you listen to music off your CD-ROM drive. • But where does your sound card do the conversion? • Hummmm…. Later is (far, far) better, because there’s lots of electrical interference inside your PC. Digital isn’t affected by this, but analog is. • So the perfect system would be all digital inside the computer and have its DAC inside the speakers • The USB promises to make this real, and Microsoft makes speakers which work this way. CSE5900 -- Intro to MM Computing -- Lecture 3

  29. MIDI & General MIDI • MIDI = Music Instrument Digital Interface • MIDI is to sampling exactly what vector is to raster graphics • A language for describing sounds • The notes • The instruments, each of which has a number • 128 instruments • Plus drum kit • The note characteristics • attack • sustain • decay • release • 2+ ways of making those notes • FM synthesis • Wavetable CSE5900 -- Intro to MM Computing -- Lecture 3

  30. The Parts of a MIDI Note • From the MIDI Manufacturers Homepage CSE5900 -- Intro to MM Computing -- Lecture 3

  31. Making MIDI • FM Synthesis • Sterile sine waves • What gave computer music a bad name • Wavetable Sound Generation • The music gives the number of the instrument • Samples of the sound of that instrument are stored in ROM/RAM on the sound card • The samples are processed to give a far better illusion of the sound of the instrument • The more samples, the better, so 4mb of samples on ROM are better than 512k. • Wavetables may also be downloaded from CD-ROMS • Wavetables can be purchased as daughterboards for better sound cards. CSE5900 -- Intro to MM Computing -- Lecture 3

  32. MIDI Quality • Well, as always there’s the trade off: • Much smaller file size • Always somewhat less quality • Infinitely cheaper to create -- only one muso necessary • May require significant CPU processing CSE5900 -- Intro to MM Computing -- Lecture 3

  33. Channels, Voices and Streams • A channel drives a speaker: • 2 channels for standard stereo • 4 channels for 3D sound (two may be faked) • 8+ channels for super sound in theatre movies • A voice is an instrument, etc. on a channel • MIDI supports a large number of voices: 32, 64. This is polyphony • The voices are superimposed, in digital or analog form, and then sent to the speakers • Again, multiple voices may load down the CPU • A stream is half voice and half channel • Lets record a sound effect, a stream • When we need it, we superimpose it on top of the sound going to a channel • The sound card and/or CPU do the work CSE5900 -- Intro to MM Computing -- Lecture 3

  34. Channels, Voices and Streams, 2 • The higher the bandwidth into the sound card • The more channels, voices and streams we can get at once • And the more processing work has to be done • So we either do more on-sound-card processing or bog down the CPU • (Sound like the issues related to 3D accelerator cards?!) • The 16 bit ISA bus worked fine for sound until we decided to want more channels, voices, streams, wavetables, etc. (But they still flourish: somebody tried to sell me one yesterday) • Newer cards use the PCI bus, and make use of it. • And use a newer generation of sound chips. • But the evolution here is relatively slow! CSE5900 -- Intro to MM Computing -- Lecture 3

  35. Games and Computer Sound • Games are one of several factors driving the evolution of graphics boards • Games are almost the only factor driving the evolution of sound cards • Who is sneaking up behind me? We need 3D. • What kind of sound does that alien make when exploded? We need lots of streams superimposed. • 3D illusion • Uses 3 speakers (woofer, + 2 satellite) and an algorithm to fox the ear by marginally delaying one stereo channel • Developed by NASA for space flight simulators • Can work well if don’t move your head • With 5 speakers, esp. with 4 channels, can work very well indeed • As the musicians are never behind you, not necessary for music. Whoops, sorry Berlioz, Allegri, Tchkovsky, etc. CSE5900 -- Intro to MM Computing -- Lecture 3

  36. Games and Computer Sound, 2 • Competing 3D positional audio standards • A3D • From Aureal Semiconductor (now defunct) • Now a non-runner • Audio Extensions .EAX • From Creative Labs (who brought us Sound Blaster) • Bought resources of Aureal (A3D) • Included A3D technology in .EAX • In Nomad, Zen and other sound card brands • DirectSound3D • From Microsoft • Part of the DirectX set of Windows APIs/extensions, including Direct3D • CRL Sensaura • Bought by Creative Technology in 2003 • Used in Xbox, PlayStation2, Nintendo GameCube, PCs CSE5900 -- Intro to MM Computing -- Lecture 3

  37. Digital Signal Processing • Now most music processing is in analog form on card. • Far better if it were all digital, with DAC and amplification on the speakers • Need DAE: Digital Audio Extraction, from CD/CD-ROM • Introduced with 24x CD-ROMs. • Theory is that we use USB to get the digital sound to the speakers • Speakers with USB connections now also have standard audio connections for the sounds and use USB for controlling the settings • Amplifiers are both on the sound card and external. CSE5900 -- Intro to MM Computing -- Lecture 3

  38. MP3 • MPEG-1, Layer 3 sound compression -- intended for movies on CD and DVD • 90+% compression possible • Compression takes about a third of the length of the music • A typical song (50mb) goes to 5mb • Is a lossy compression, so the quality goes down, but not much • No encryption in any way • No “watermark” (watermark = a secret pattern of bits somewhere which indicates the source of the copy) • Much music publisher panic with the popularity of the format. • Much more music publisher panic with the IPod, which can store an entire music library in MP3 formt CSE5900 -- Intro to MM Computing -- Lecture 3

More Related