What is Pulse Code Modulation (PCM)

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In a brief sentence, pulse code modulation is a method used to convert an analog signal into a digital signal. So that it can be transmitted through a digital communication network, and then converted back into the original analog signal.
The PCM process includes three steps: Sampling, Quantization, and Coding.
In the sampling process, the magnitude of the analog signal is sampled regularly at uniform intervals. The obtained values are called samples.
For a 4 kHz voice channel, the sampling rate is 8000 Hz, which means the signal is sampled 8000 times per second.
The samples will then be converted to digital numbers as we will see in the quantization process.
Quantization is the process of converting the obtained samples into discrete digital values. The most basic type of quantization is called uniform quantization.
In an uniform quantization, the vertical axis, which represents the amplitude, is divided into equal sized steps. As shown in this figure, the range between 1 volt and -1 volt is divided into 16 steps, each step represents 0.125 volt.
All the samples whose amplitude falls within an step, take the same step value.
However, the quantization process introduces an error. This is because that the real amplitude of a sample is replaced by an approximate value. This error is called quantization noise or quantization distortion.
In uniform quantization, the quantization distortion presents a problem. For example, let's assume a quantization error of 0.05 volt, if this happens at a high level signal, such as 5 volt, the noise ratio is 0.05 volt divided by 5 volt, which is 1%, not too bad. But if the same quantization error happens at a low level signal, such as 0.5 volt, the noise ratio is 0.05 volt divided by 0.5 volt, which is 10%.
Simply put, for uniform quantization, the signal to noise ratio is good at high level signals, but bad at low level signals. That is why non-uniform quantization was introduced.
In non-uniform quantization process, the steps are not of equal size. Small steps are used for small signal values and large steps for large values. The purpose of doing so is to achieve that the signal-to-noise ratio is nearly independent of the signal level.
This is done by favoring low-level voice over higher-level voice. In other words, more code groups are assigned to speech at low levels than at the higher levels, progressively more as the level reduces. This is shown in this figure.
There are two types of non-uniform quantization methods in popular use today. They are the A-law and the u-law. Let's first look at the A-law.
A law follows the logarithmic formula listed here, with A equals to 87.6.
We can see that the curve consists of linear piecewise segments, seven above and seven below the origin. The segment just above and the segment just below the origin consists of two linear segments. Counting the collinear elements by the origin, there are 16 segments. Each segment has 16 8-bit PCM codes assigned. These are the codewords that identify the voltage level of a sample at some moment in time.
Each codeword, often called a PCM "word", consists of 8 bits. The first bit tells the receiver if the sample is a positive or negative voltage. We can see that all PCM words above the origin start with a binary 1, and those below the origin start with a binary 0.
The next 3 bits in sequence identify the segment. There are eight segments above the origin and eight below the origin.
The last 4 bits, shown as XXXX, indicate exactly where in a particular segment that voltage line is located.
The second is called u-law. It follows the logarithmic formula listed here with u equals to 100.
The North American T1 system uses the u-law quantization and coding process. The process is similar to that of A-law.
Colin Yao
Sales Manager
Fiber Optics For Sale Co.
1532 Centre Pointe Dr.
Milpitas, CA 95035
Web: www.fo4sale.com

[@agstechnicalsupport]

A good introduction into Pulse Code Modulation (PCM). Thank you !

[@DieWieselShow]

Big thank you from Germany!

[@aRtaBxaR]

Simply make complicated topic so simple. Thanks.

[@styno2010]

Thank you for this video and keep up the good work.

[@junaidhassan2176]

great video..this video makes ur PCM concept more clear.

[@ashishnegi1985]

Thanks Colin. I was very worried about the topic. It helped me alot

[@yashkothari823]

Thank you for the wonderful video.

[@delssyentertainments7411]

Thank you so much, This very clear and beficial.

[@z3jlewhhda376]

If PCM is used to convert sampled analog to digital, then why there is sampling in the process of PCM? It shoud not be Quantization and encoding only?

[@collicorporation7960]

Thanks so much!

muy bueno el tutorial. me sirvio bastante. Gracias por subirlo.

[@georgeclooney8541]

Great video sir

[@lukel1724]

Great explanation, thanks!

[@janeyritter]

DOES this make a pulse noise audible to the ear? We have our DSL company laying lines and since then we hear a pulsing noise inside and outside of our home. The noise caused a seizure in me. What would make such a noise on the electric line and emf inside our home?

[@franknomustard]

Good job. Putting on my channel for reference.

[@karimkhan1312]

i am impressed by your lecture

[@JSB1729]

Thank you very much for this video.

[@snehaelizebeth6146]

Great thanks at the last minute!

[@AkhilDakur]

Its really a very good video the information is opt to the point. Thanks

[@rejj0313]

Great Info, Well Defined

[@komalmaurya99]

Pcm works on which type frequency microwave or audio frequency please reply me

[@defaultproductionsuk]

Thank YOU! easy to follow really helpful and cool accent :D

[@lance8080]

Doug Ware Indians have the worst English tutorial videos.

[@Xaeravoq]

it is my understanding that with u-law the PCM words are swapped with 0 being positive and 1 being negative. it looks like you kept them the same as a-law. why is that?

[@sajidbashir8617]

good explanation of pcm

[@ankansharma4897]

awesome explanation thanks a lot. please upload more videos on communication and information coding theory

[@Tripdin]

Thanks, it was a very nice and informative presentation

[@danchisholm1]

Thanks Colin - very helpful.

[@meso2nono]

Great video. Thanks for uploading.

[@ojesnautiyal1100]

hey dude,grt video ....can u post some more video on frequency and amplitude modulation...

[@gaspardgashema1638]

Very helpful tutorial.I appreciate you very much and I wish you having more knowledge for informing and updating in Technological.

[@elisokal]

Thanks Colin. Well done.

[@siddharthamondreti9538]

Useful as a last minute revision.. :)

[@lance8080]

Siddhartha Mondreti glad its not an indian doing this video can’t understand them and their all over the place.

[@siddharthamondreti9538]

@@lance8080 Noted 😊. Next time we will think of people like you who have Low IQ and finds it difficult in understanding it. Anyway, I would suggest you to clean up your brain (full of hatred and negativity) a bit to speed up your thought process, may be that way you can atleast come close to ours. 😊

[@hueance]

very well explained absolutely amazing fellow

[@sandeshmagar4552]

What is the effect in PCM if the quantization level is changed to higher or lower?

[@nbafun8648]

is this channel or source coding ??

[@pabloluciano3504]

very good video

[@wasimtana1007]

Its a good video , thank you !

[@giridharyadav9105]

can u make a video of coded modulation in optical fiber communicationd

[@aniljacob7630]

Nice and short!!!

[@manojnegi2568]

is there any real world example of sampling?

[@AlvaroDevLabs]

Excelent tutorial thank you very much

[@privilegenkomo9444]

helpful information, thank you

[@UdayKumar-bm1el]

great video!!!

[@sagardubey9857]

very good tutorial

[@anaghasuresh1679]

nice and interesting video..

[@rickveens92]

wow very clear. can you do PCM, ADPCM, IMA/DVI ADPCM?

[@valriebrown2748]

great tutorial, thanks alot

[@wen-qinghuang7830]

It's very clear.

[@Anonymous-du4iy]

thanks more the help man!

[@devashishs7061]

nice tutorial,thanks

[@b4dan92]

good video! Thanks!

[@carolynjohnson461]

thanks reading this i was trying to understand fuses to my check eng lite to fix myself sounds like one of the fuses

[@rahul25bala]

Awesome. Thank You :)

[@沈遠博]

Thanks! It helps a lot.

[@rajdll123]

Dude, this is awsm.

[@krishnavijay4413]

Very Helpful...

[@kesinenisireesha7799]

Nice video

[@sheikhmaqbool4527]

Nice one

[@sindrck]

good work n thank u very much

[@tharindawicky]

very good lesson thanks..:)

[@shatarupabepari5394]

thank u sir for your video

[@aliadil9411]

Good job, thanks

[@yonasberhanu2187]

this is very important tutorial 10q

[@rahulbiswash8238]

very nice

[@ssknsj]

good video

[@hesahesa5665]

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[@yagzyalcntas553]

i agree with you... lol

[@hellcatspangledshalalalala717]

you sound like JIN YANG from silicon valley

[@jayantkapila1794]

jin yang: i do not respect you, u are a fat and a pooa... erlich: jin yang!!!!!!!!!!!!

[@ergolfer148]

good stuff thanks!

[@alejandroalarcon6670]

Hi good day; query the number of possible codes is equal to the level of cuaticantificacion?

[@omarggcode3942]

YOU ALL FORGET WHERE IS THE CODING PHASE !!!!!???

[@ballasonia7287]

short. and. nice

[@anaghadevi6724]

Thank you

[@kabelotshutse1280]

Multiplexing

[@swordfish2r2011]

Thanks Yao

[@51anirudh]

merci!

[@pritamdey7640]

Good..!!

[@ShirleyAnderson-q1e]

Aditya Locks

[@prashantgontia5484]

nice

[@anwarshome]

Awsome

[@tago1729]

you're language tough..

[@yagzyalcntas553]

maybe you should consider YOUR* language first ;)

[@Madison-ut6bz]

dont think too much

[@parveenrohilla6160]

NOT BAD

[@JamieBrown-s4i]

Lesch Camp

[@totylow]

Whom else saw the entire video and understand none of it as me? Damn! i just wanted to know if PCM is better than DTS or Dolby Digital.

[@PizzWisard]

PCM is a process of capturing sound. Most file formats like wav etc. are just wrappers for PCM. Seeing as WAV is a lossless format and Dolby Digital is technically lossy, PCM would be better in terms of audio quality. But it still depends on the sample rate and bit depth. You could still have a PCM at 8-bit and it would sound like pure shit but nobody would do that.

[@jonathanrawlinson468]

Great thanks! :)