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L 19 Electronic Sound- Analog and Digital. Electronics in Music Intro Basic Analog Electronics Digital Audio . Edison Phonograph - 1879. Cylindrical Phonogram (Thomas Edison 1877 ). (Youtube video). Acoustic Recording Session ca. 1920.
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Electronics in Music • Intro • Basic Analog Electronics • Digital Audio
Cylindrical Phonogram (Thomas Edison 1877 ) (Youtube video)
Voltage (Potential Drop)The potential energy an electron has divided by its charge
Ohm’s LawThe current (charge per unit time) flowing through a circuit element is equal to the potential drop across this element divided by the resistance of the element. I= V/R
I V R • Suppose the current is 3 A and the voltage is 6 V. What it the resistance? • 3 W • 2 W • 1/2W • d) 1/3 W
Power Amplifier Driving Loudspeaker I Z= 8 W V Signal Source Amplifier Speaker
We can write the number 752 as2x100 + 5x101 + 7x102Similarly,we could use the base 2 instead of 10, e.g.3 = 1x20 + 1x21,which we represent as 11.Hence the binary 01 is our old friend 2.Keep in mind that the numbers written are the coefficients of 100 , 101 , etc.11 and 01 are called 2-binary digit (bit) numbers.
Note the possible combinations of 2 bits:00 = 001 = 2 10 = 1 11 = 3,4 possible combinations = 2nwhere n= # of bits
Someexamples of 4-bit binary numbers0000010000100011The 2nd of these binary numbers, for example, corresponds to the number 0x20 + 1x21 +0x22 + 0x23 = 2Note that there are 24 = 16possible combinations for a 4-bit binary number.
Note also that we have chosen the sequence as the coefficient of 20 first, then 21, then 22 , etc.This convention is used by many electrical engineers, but it is arbitrary (e.g. Wikipedia uses the opposite convention) .
Digital Audio - What is it? • Really a method to capture and transform audio signals for the purpose of storage, transmission, manipulation, and playback • Digital Approximation of the real event and sound waves • Requires A/D and D/A Converters • Devices used to change analog to digital and back again. • These are generally found on computer sound cards • A/D converters perform sampling of waveforms • D/A converters convert digital data back into a waveform • Employ various forms of encoding and decoding the bit stream using CODECS (Compressor/De-compressors)
Suppose we wish to represent a complex wave form digitally.We will now introduce the concept of sampling the wave form.The idea is to measure the amplitude at various times during the cycle and represent those amplitudes digitally.
Analog to Digital Recording Chain ADC Microphone converts acoustic to electrical energy. It’s a transducer. Continuously varying electrical energy is an analog of the sound pressure wave. ADC (Analog to Digital Converter) converts analog to digital electrical signal. Digital signal transmits binary numbers. DAC (Digital to Analog Converter) converts digital signal in computer to analog for your headphones.
Analog versus Digital Analog Continuous signal that mimics shape of acoustic sound pressure wave Digital Stream of discrete numbers that represent instantaneous amplitudes of analog signal, measured at equally spaced points in time.
Analog to Digital Overview Sampling Rate How often analog signal is measured [samples per second, Hz] Example: 44,100 Hz Sampling Resolution [a.k.a. “sample word length,” “bit depth”]Precision of numbers used for measurement: the more bits, the higher the resolution. Example: 16 bit
Common Sampling Rates Which rates can represent the range of frequencies audible by (fresh) ears? Most software can handle all these rates.
7 6 5 4 3 2 1 0 3-bit Quantization A 3-bit binary (base 2) number has 23 = 8 values. Amplitude Time — measure amp. at each tick of sample clock A rough approximation
14 12 10 8 6 4 2 0 4-bit Quantization A 4-bit binary number has 24 = 16 values. Amplitude Time — measure amp. at each tick of sample clock A better approximation
