 Hello friends, myself Mr. Ilya Arjanani, assistant professor from the Department of Electronics, Vulture Institute of Technology, Solapur. Today we are going to see the topic digital audio capture which comes under the subject audio video engineering. So what are the learning outcomes in this topic? At the end of the topic, students are able to understand the term what is meant by sound and what are its different types. They can also illustrate the characteristics of sound and how the sound is captured and regained back. So basically what is a sound? So sound consists of spoken words, voice, music and even noise. It is the basic relation between vibrating object that is the sound source, the transmission medium, the receiver and the perceptor. In human body, the perceptor is nothing but the brain of the human body. The sound waves always travel away from the source and hence we can say that sounds are rapid vibrations that are transmitted as variations in air pressure. So what are the characteristics of a sound wave? So the above diagram shows a sound wave which has two cycles and the one cycle generally denotes the time of one cycle and the x-axis generally denotes the distance along the wave which is traveled. So sound waves are generally the periodic type of waves and are having a repetitive manner. These waves are irregular in their behavior when noise affects them. So basically the noise affects these sound waves in the channel as the sound waves passes through the channel. The unit for sound wave is hertz and one cycle is equal to the one hertz and sometimes the cycle is of one kilohertz. So what are the characteristics of a sound wave? So here there are two important characteristics first frequency and second is amplitude. Frequency is defined as the rate at which sound is measured and the unit of frequency is hertz. So for this we can take the example again here the y-axis generally denotes the amplitude and the x-axis generally denotes the distance along the wave and the distance between the two crest that is this one and the second one this generally denotes the pitch of the sound. The high frequencies are generally clearer and sharper which are having a high pitch. So amplitude it is generally defined in terms of loudness and intensity of a sound. So as the sound is louder the amplitude is higher. So here we are seeing the two basic examples which are of two different instruments. First we are seeing the piano and second one is the flute. Here if you see that when the finger is moved on the keynotes of the keyboard from left to right then the left is having the higher sound and as we progress towards the right hand side to the last key the sound goes on decreasing. This characteristics generally show the same effect here initially the left key is having the high amplitude and as we go down it goes on decreasing. Similarly to the we can say we can take an example of a flute here if you can see the flute is having some high amplitude and some low amplitude again it is having high amplitude and low amplitude this goes on increasing and decreasing as the flute is having some holes on it and due to the variations in the air pressure as we move our fingers on on the hole then these amplitude occur or these variations occur into the amplitude. So how digital audio is captured and play back. First the speech which is nothing but air pressure variations these are converted into the digital one. Firstly these are given to the mic or the microphone these are then converted into electrical signals these electrical signals are then converted into digital signals or we can say into a binary signal with the help of a ADC which is nothing but analog to digital converter. These digital audio signals are regained back in terms of sound on the speakers or generally the output is taken on the speakers and this is done by using a DAC which has an input of the discrete binary signal which then converts the digital signal into the electrical one and these are given to the speakers which are the transducer which convert electrical signals into the sound signals. So ADC process what is an ADC process here analog to digital conversion takes place of a sound wave first in this the sound wave is analyzed for seeing where are the variations where are the high and low variations then after analyzing is done sampling process is used for the conversion and in this way if you look at the waveform A here the points are given here generally the sound wave is analyzed where it is having the zero where it is going to a high this generally denotes the maximum amplitude then it is again going towards the zero and here it goes to the zero again so after the analysis then here you can see the samples are taken at the different points and generally see denotes the samples of a sound wave so in this way the sampling process takes place. So how we are going to calculate the size of a digital audio signal for this for calculation of size of digital audio signal following formula is used rate into duration into resolution into the number of channels divided by 8 rate generally denotes the sampling rate duration generally denotes the duration of a sound wave resolution generally denotes the variations in the sound wave and number of channels which include the stereotype of the channels and it generally denotes the bits which are going to be used for the conversion process so for this we can take an example so calculate the size of a digital audio signal with parameters as 1 minute 44.1 kilohertz 16 bits stereo sound which is having number of channels as 2 here 1 minute generally denotes the rate 44.1 kilohertz generally denote the resolution and 16 bits generally denote the rate and stereo is nothing but here we are considering a stereo sound hence the number of channel used here are 2 so by using the this formula you can find out the answer so the answer for this is pause this video and calculate the answer yes you are absolutely correct the answer is 176.4 bytes so this generally indicates the size of digital audio signal here the size of digital audio signal is nothing but the signal audio signal which is recorded and which is reproduced by using the two processes so this is the example to calculate the size of digital audio signal with parameters as 2 minutes 34.5 kilohertz 15 bits stereo sound here also we are going to use stereo sound which is having the number of channel as 2 so calculate the size of digital audio signal so these are the references for you by using this you can solve the problems and you can go through the theory also thank you for watching