Art 299 Sound, Audio, Acoustics as Creative components Dr. J. Parker Fall 2009

Sound What we hear as sound is caused by rapid changes in air pressure! It is thought of as a wave, but that can be confusing since we are immersed in the medium. A wave seems to be on the surface.

Sound is 3D Sound sources is at the centre of a sphere. Pressure changes (higher, lower, higher …) move outwards from the source.

Pressure and Amplitude Loudness is a matter of how big the pressure change is. If we let normal ambient air pressure be 0, then sound amplitude is +x to –x for some way to measure pressure. Air pumps at gas stations here use Pascals, but we can use whatever we like.

PHYSICS ALERT !! 1 Pascal = 1 Newton per square metre Standardized normal air pressure is: P 0 = 2 X N/m 2 = N/m 2 = 20μ Pa. Why do we care? Because a decibel, the standard measure of sound level, is: 10 log 10 where p is the rms pressure of the sound.

Who cares? All sound folks use decibels, or db. You get to know (feel) how loud things are after a while. Threshold of Hearing (TOH) 0 dB Rustling Leaves 10 dB Busy Street Traffic 70 dB Front Rows of Rock Concert 110 dB Military Jet Takeoff 140 dB Instant Perforation of Eardrum 160 dB

How loud is it? The sound of leaves is 10 db. The sound of a pencil dropping is 20 db. How much louder is that ? 10 times! Decibels are based on powers of 10. If one sound is 10 x times more intense than another sound, then it has a sound level which is 10*x more decibels than the less intense sound.

Frequency If you stand in one place, the pressure waves will pass you. The number of peaks that pass per second is the frequency. Measured in Hertz (Hz), formerly cycles per second. 60 Hz = low hum 440 Hz = ‘A’ on piano 4000 Hz = limit of telephone (voices)

Frequency If we draw a curve that represents pressure VS distance we can see that sound does look like a wave.

Frequency Since the speed of sound in air is a constant (pretty much) then the number of peaks that pass is a second is related to the distance between them is a fixed way. Also, the horizontal axis could be distance just as easily as time.

Frequency V = /f where v is speed of sound, f is frequency.

Amplitude

Frequency Frequency is a precise way to specify pitch. A 440 E above C Summed Oboe A Oboe E Phantom B 3960

Frequency

Interesting sidebar The speed of sound is different in different media (air and water). When a sound moves from one medium to another, part of the sound is transmitted, part is reflected back!

Sound can reflect

Multiple sounds What we hear with multiple sounds is the sum of all of them.

Sound Systems/Tech A sound system is a collection of electronic components designed to record and display sound. Details depend on applications: Theatre: large output, many speakers Studio: large input, many microphones

Microphone Converts air pressure differences into electrical voltage.

Microphone

Speakers For display of audio.

Amplifier Changes volume (voltage/current/power) levels of a signal. Needed to get good sound levels from a speaker.

Mixer Control volumes of multiple inputs into (multiple) outputs.

Complete Sound System

Recording How can sound be recorded? How can it be stored on a computer? What tools do we use for this? Where do the wires go? Why am I doing this? It is still sound if it is on a hard drive? How much disk space do sounds need?

Recording To record sound on a computer is very simple. Recall that microphones change sound (pressure) into voltage (electricity). A computer ‘sound card’ can change voltages into numbers (just as we do: 12 volts, for instance) which can be stored in a computer memory. A sound is therefore a sequence of numbers that represents voltages (that represent pressure).

Digital Sound How BIG the numbers can be dictate accuracy of voltage samples ->volume or amplitude. 8 Bits (binary digits) can store numbers between 0 and 255 (256 different frequencies) 16 bits has different frequencies. Called depth or quantization.

Digital recording How fast you play the samples back dictates frequency. Obviously one plays them back as fast as they were recorded. However, more samples per second means higher frequencies can be recorded.

Sampling

Quantization Distortion Quantization is the process of selecting whole numbers to represent the voltage level of each sample. The A/D converter must select a whole number that is closest to the signal level at the instant it’s sampled. This produces small rounding errors that cause distortion. Quantization distortion increases at lower levels because the signal is using a smaller portion of the available dynamic range, so any errors are a greater percentage of the signal.

Clipping

File Sizes Sampling Rate x Resolution x Number of Channels x Time in Seconds / 8 = File Size (in Bytes) x 16 x 2 x 60/8=10,584,000 /minute

Sizes Bytes per minute, uncompressed. Sampling Rate Resolution Number of Channels File Size 44, ,584,000 44, ,292, ,646, ,323, ,000

Recording sound – MAX OS X

Recording Sound – Windows XP Sound recorder To open Sound Recorder, click Start, point to All Programs, point to Accessories, point to Entertainment, and then click Sound Recorder. Audacity Sound Forge

Sound Effects V/index.html

Edit: To alter to fit a purpose Sound files contain audio stored as samples. We can change the value of any sample or group. We can copy samples from one place (time) to another. We can delete samples.

We need an interface Samples are averages of sound values over time. Not a good abstraction. Originally, editing was done using audio tape. Tape was physically cut with a blade and then taped back together.

Old Style Tape Editing Cut editing (also known as destructive editing) consists of physically cutting magnetic recording tape, removing an unwanted portion and rejoining the recording tape with a special adhesive backed splicing tape. Monophonic and stereophonic 1/4 inch tapes were traditionally edited in this way. Cassette tapes can be cut edited but it is difficult to locate the precise edit point. The technique is sometimes useful for retrieving damaged cassettes. Multitrack tapes (4 or more tracks) are not cut edited..

Tape Editing Removing a section of 1/4 inch tape 1.Play the tape until you hear the first cue, that is, the sound at the beginning of the section you intend to remove. 2.Put the tape recorder into edit mode. (See the operator's manual.) 3.Rotate the tape spools by hand with the tape against the replay head, (usually the one on the right).

4. Using a chinagraph pencil, mark the tape at the beginning of the section to be removed. 5. Mark the tape at the second cue, e.g. at the end of the section to be removed. 6. Pull the tape away from the replay head and lay it in the guide of the editing block, oxide side down.

7 Line up your chinagraph mark with one of the diagonal slits in the editing block. Choose the 450 (45 degree) slit for a stereo recording, the 600 slit for a mono recording or the 900 slit if you are removing clicks. 8 Cut the tape by running the corner of a single- sided razor blade along the slot. The corner of the blade should run along the bottom of the slot in the editing block. It does not matter that the corner of the blade becomes blunt because that is not the part of the blade that slices the tape.

9Now cut the tape at the other chinagraph mark 10Remove the unwanted section of tape but keep it safe in case you need to replace some or all of it 11Slide the two ends of the tape together in the editing block. The two cut ends should just butt together. There should be no overlap and no gap between the ends.

12. Cut about 2cm of adhesive splicing tape. Touch one end of the splicing tape on to the side of the razor blade, so that it lightly sticks there.

13. Use the blade to transport the cut length of splicing tape to the editing block.

14. Stick the length of splicing tape over the butt join and press out any air bubbles with your finger nail..

15. Remove the magnetic tape from the splicing block. 16. Play the tape at a good listening level and listen to the edit point. As the edit passes the replay head there should be no change in the level (loudness) or quality of the foreground speech, music, e.t.c. no change in the level or quality of the background noise no change in the rhythm of the speech or music

Anyone wish to try this??

So, how does this translate into Digital?? Let’s use GoldWave: it is free (evaluation version), and is relatively full featured.

The sound (tape) is in a window Time advances from left to right; volume (voltage, intensity) is up/down. There Are two channels here (stereo) Time (in seconds)

The controls Time advances from left to right; volume (voltage, intensity) is up/down. There Are two channels here (stereo) New File Open File Copy To Clipboard Save selection Delect Selected data Paste Into new window Which channel Scale

The device controls Time advances from left to right; volume (voltage, intensity) is up/down. There Are two channels here (stereo) Play Rewind Record Left Channel User play (looping) Volume Balance Speed Right channel

Editing – Grab, cut, paste Right Click on right side Of sound to be copied/ deleted Left Click on left side Of sound to be copied/ deleted Then select cut or copy or delete, or use del or ctl-x or ctl-c

Editing – Sound Forge Advantage – you can hear the sound as you move a cursor along the time line.

Editing – ‘Colors’ From the computer commercial on TV Kira Willey - Colors.MP3 Final edit Colors – edit 1

Recording – microphone work Sound forge

Recording – Audacity Available at Open source!

Recording – Audacity Goldwave Sound Forge Audacity