The Basics of Digital audio

The theory of digital sound

Basic signal theory

As you probably know, sound is air which is moving very quickly. The speed of these movements is called "frequency", which is a very important property of sound, especially music. The frequency of a sound is measured in Hz (=Hertz, named after a man called Hertz :-/ who did a lot of research into sound and acoustics some time ago). Most people can hear frequencies in the range between 100Hz-15000Hz. Some people can hear very high frequencies above 19000Hz, but scientists always assume that the human ear is able to discern frequencies between 20Hz-20000Hz, since those numbers make their calculations a lot easier.
Here's a few examples of different frequencies, if you'd like to play with them for a while:

60 Hz	440 Hz	4000Hz	13000Hz	20000Hz
-very- low	A'	audible	ouch!	too high

Another very important property of sound is its level; most people call it volume. It is measured in dB (=deciBell, named after a man called deciBell (NOT!!) all right, his real name was Bell, but he did invent the telephone and that is why us Dutch people still say 'mag ik hier misschien even bellen?' when they want to use your phone).

So why don't we measure loudness in Bell instead of deciBell? Well, mainly because your ear really can discern an incredible amount (1.200.000.000.000, that's 11 zeroes) of different loudness levels, so they had to think of a trick(which I'm not going to explain here, sorry!) be able to describe an incredible range with only a few numbers. They agreed to use 10th's of Bells, deciBells, dB, instead of Bells.

Most professional audio equipment uses a VU meter (=Volume Unit meter) which shows you the input or output level of your equipment. This is very convenient, but only if you know how to use it: A general rule is to set up the input and output levels of your equipment so that the loudest part of the piece you want to record/play approaches the 0dB lights. It is important to stay on the lower side of 0dB, because if you don't, your sound will be distorted badly and there's no way to restore that. If you're recording to (analog!) tape, instead of (digital) harddisk, you can increase the levels a bit, there is enough so-called 'headroom' (=ability to amplify a little more without distortion) to push the VU-meters to +6dB. There is some more information on calibrating equipment levels inthe recording section below.
Some examples of different levels, if you'd like to play with them for a while:

0,0dB = 100%	-6,0dB = 50,0%	-18,0dB = 12,5%	+6,0dB = 200%
maximum level	half power	very quiet	a little too loud-a lot of distortion

Okay, now that you know the most important things about sound, let's finally go to the digital bit (ooh, a pun :-/ ): I've just told you about the properties of 'normal' (analog) sound. Now I'll tell you what the most important properties of digital sound are.

Digital Audio Theory

First of all, the famous 'sample rate'. The sample rate of a piece of digital audio is defined as 'the number of samples recorded per second'. Sample rates are measured in Hz, or kHz (kiloHertz, a thousand samples per second). The most common sample rates used in multimedia applications are:

8000 Hz	11025 Hz	22050 Hz
really yucky	not much better	only use it if you have to
Professionals use higher rates:
32000 Hz	44100 Hz	48000 Hz
only a couple of old samplers	ahh, what a relief	some audio cards, DAT recorders

Some modern equipment has the processing power required to enable even higher rates: 96000Hz or even an awesome 192.000Hz will possibly / probably be the professional (DVD?) standard rates in couple of years. The advantages of a higher samplerate are simple: increased sound quality. The disadvantages are also simple: a sample with a higher samplerate requires an awful lot more disk space than a low-rate sample. But with the harddisk and CD-R prices of today that isn't too much of a problem anymore.

....But Why?!

To answer that, let's look at a single period of a simple sine wave:

it starts at zero.. ..then it goes way up.. ..then it goes back to zero.. ..then it goes way down.. ..then it goes back to zero. and so on...Sine waves sure have monotonous lives ;-)

a sine wave

When recording a certain frequency, you will need at least (but preferably more than) two samples for each period, to accurately record it's peak and valley. This means you will need a samplerate which is at least (more than) twice as high as the highest frequency you'd like to record, which, for humans, is around 20000Hz. That's why the pro's use 44100Hz or higher as the minimum samplerate! They can record frequencies up to 22050Hz with that. (Now you know why an 8000 Hz sample sounds so horrible: it only plays back a tiny part of what we can hear!)

Using an even higher samplerate, like 96000Hz, you can record higher frequencies, but you won't hear things like 48000Hz anyway. That's not the main goal of those super-rates. If you record at 96000Hz, you will have more than four samples for each 20000Hz period, so the chance of losing high frequencies will decrease dramatically! It will take quite a few years for consumer level soundcards to support these numbers, though. There are a few pro cards which already do, but you could easily buy a small car for the same money...

That's enough about frequency for now. As I said before, another very important property of sound is its level. Let's have a look at how digital audio cards process the sound levels.

DYNAMIC RANGE

The capacity of digital audio cards is measured in bits, e.g. 8-bit soundcards, 16-bit soundcards. The number of bits a sound cards can manage tells you something about how accurately it can record sound: it tells you how many differences it can detect. Each extra bit on a sound cards gives you another 6dB of accurately represented sound (Why? Well, Because. It's just a way of nature). This means 8-bit soundcards have adynamic range(=difference between the softest possible signal and the loudest possible signal) of 8x6dB=48dB. Not a lot, since people can hear up to 120dB. So, people invented 16-bit audio, which gives us 16x6dB=96dB. That's still not 120dB, but as you know, CD's sound really good, compared to tapes. Some freaks, that's including myself ;-) want to be able to make full use of the ear's potentials by spending money on soundcards with 18-bit, 20-bit, or even 24-bit or 32-bit ADC's (Analog to Digital Convertors, the gadgets that create the actual sample) which gives them dynamic ranges of 108dB, 120dB, or even 144dB or 192dB.

Unfortunately, all of the dynamic ranges I mentioned are strictly theoretical maximum levels. There's absolutely not a way in the world you'll get 96dB out of a standard 16-bit multimedia sound card!!! Most professional audio card manufacturers are quite proud of a dynamic range over 90 dB on a 16bit audio card. This is partly because of the fact that it's not that easy to put a lot of electronic components on a small area without a lot of different physical laws trying to get attention. Induction, conduction or even bad connections or (very likely) cheap components simply aren't very friendly to the dynamic range and overall quality of a soundcard. But there's another problem, that will become clear in the next paragraph.

Quantization noise

Back in the old days, when the first digital piano's were put on the market, (most of us didn't even live yet) nobody really wanted them. Why not? Such a cool and modern instrument, and you coould even choose a different piano sound!

The problem with those things was that they weren't as sophisticated as today's digital music equipment. Mainly because they didn't feature as many bits (and so they weren't even half as dynamic as the real thing) but also because they had a very clearly rough edge at the end of the samples.

Imagine a piano sample like the one you see here. It slowly fades out until you here nothing.
At least, that's what you'll want... As you can see by looking at the two separate images, that's not at all what you get... These images both are extreme close-ups of the same area of the original piano sample. The highest image could be the soft end of a piano tone. The lowest image however looks more like morse code than a piano sample! the sample has been converted to 8 bit, which leaves only 256 levels instead of the original 65536. The result is devastating.

Imagine playing the digital piano in a very soft and subtle way, what'd you get? some futuristic composition for square waves! That's not what you paid for ;-) This froth is called quantization noise, because it is noise that is generated by (bad) quantization.

There is a way to prevent this from happening, though. While sampling the piano, the soundcard can add a little noise to the signal (about 3-6dB, that's literally a bit of noise) which will help the signal to become a little louder. That way, it might just be big enough to get a little more realistic variation instead of a square wave. The funny part is that you won't hear the noise, because it's so soft and it doesn't change as much as the recorded signal, so your ears automatically forget it. This technique is called dithering. It is also used in some graphics programs e.g. for resizing an image.

Jitter

Another problem with digital audio equipment, is called jitter. Until now, I've always assumed that the soundcard recorded the sample at exactly 44100Hz, taking one sample every 1/44100 second. Unfortunately that is -totally- unreal. There *always* is a tiny timing error which causes the sample to be taken just a little too late or just a little too soon.

Does this make a big difference then? Well, you could start nagging about everything, but then you'd probably have bought a more expensive soundcard in the first place. The really bad part is that jitter is frequency dependent. Because it's related to the timing of the sample, it can change the recorded frequencies just a little. If it records a sample just a little too soon, the card thinks that the recorded frequency is a little lower than it really is. This is noticable at frequencies below 5000Hz but especially bad at the lowest frequencies, because the influence of a little error is much bigger there. Typical jitter-times go between 1.0 x 10 ^-9seconds (that's a NANOsecond, read:almost nothing) and 1.0 x 10 ^-7 seconds (that's a hundred NANOseconds, not a lot more) but they make the difference between a 'pro' sound and a 'consumer' sound on e.g. different CD-players.

Digitizing sound

When you record a sample with your sound card, it goes through a lot of stages before you can store it on your hard disk as a sound file. Fortunately you don't have to worry about these stages, because modern sound cards and samplers take care of them for you.
I'm going to be a big bore and tell you about these stages anyway.

Let's see what happens when you press 'rec':

The sound card starts a very accurate stopwatch (the samplerate).	Analog to Digital Conversion process
Then it transforms the sound coming in: it simply cuts off the very high frequencies which it cannot handle. This cripples the sound a lot, but it is required to prevent even more serious damage to the sound, which would make the sound unrecognizable. This is a low-pass (cut the 'high' frequencies, let the 'low' frequencies pass through) anti-aliasing (smoothing, blurring) filter (because it takes away some parts and leaves the rest)
Every time the stopwatch has completed a cycle, the sound card's ADC looks at the filtered input signal. It calculates how loud the incoming sound is at that exact moment in time (very much like a microphone would measure air pressure) and transforms the loudness level into the nearest digital number.
and shouts that number to the computer, which stores it somewhere in memory, probably on a hard disk.

Sound card manufacturers put a brickwall-filter (look at the image below!) in their sound card, to prevent a very nasty side-effect called 'foldover'. Foldover is a pretty difficult concept, but I'll try to keep it simple.

It's more or less the same thing that happens when you look at a car's wheel when it drives past you very quickly. You'll sometimes see the wheel moving backwards. Another example can be found in old western movies where you'll see a train going by. The 'wheels' of the train will be moving backwards too, if the train's going fast enough.

All these 'illusions' are foldover-effects. They occur when a fast system at regular intervals analyzes something which is moving even faster than the system itself.
When recording at 22050Hz, your sound card will simply not be able to record any frequencies above 11025Hz, because you need at least two samples for each period, as described above. Without the low-pass filter, the sound card would blindly try to record those frequencies. But afterwards, when you play back the sample, you'll hear a totally different frequency instead of the original one. Just like the car's wheel that seems to be moving backwards, while it really isn't.
(The frequency you'll actually hear equals the sampling frequency minus the original frequency, e.g. 22050-12050=10000Hz, instead of the original frequency, in this case 12050Hz).

a brickwall filter at 4000Hz

Therefore, the maximum frequency that can be recorded with a certain sample rate, is half the sample rate. That frequency is called the Nyquist frequency, sometimes abbreviated to f_N, after a man named Harold Nyquist, who worked at Bell Telephone Laboratories and more or less invented audio sampling. A big guy in digital audio. Anyway, to prevent all that from happening, the sound card manufacturers put a special filter in their card (see figure of brickwall filter on the right).

This low-pass filter removes high frequencies like any equalizer or Hi-Cut Switch does, except it is *much* more agressive. You can see that the filter allows all sound below 1000Hz to pass through, and that it gives the frequency range of 1000Hz-3500Hz a small boost. (This boost is necessary to be able to cut off the higher frequencies with such violence.) Frequencies above 4000Hz are eliminated extremely agressively. That is why they call it a brickwall-filter, because of the wall-like slope.

The filter displayed above might be used for a sample rate of about 8000Hz, since an 8000Hz sample has a Nyquist frequency, the maximum recordable frequency, of 4000Hz. This makes it very important to choose the appropriate sample rate for your sample; that is, if you've got a legitimate reason not to record at 44100Hz, or higher ;-)

Read more: http://ilhamnurulresources.blogspot.com/#ixzz1DtxEowFZ

Secrets All Women Keep

We women are well aware that most of the time we're a profound mystery to men. And for the most part, we like it that way. But the thought has occurred to just about every woman: Would it really be so bad if he knew _________ about me? Wouldn't it help him understand me better? And more importantly, Wouldn't he annoy me less if he knew what I really wanted?

So for the benefit of women everywhere (and for your benefit too, guys—remember, a happy woman makes for a much happier man), we're going to let men in on a little of what really makes us tick, deep down. Read on for 11 near-universal secrets of womankind. Some may shock you, others may be things you've suspected for a long time (but never had the nerve to ask about). But know this: the woman in your life? She's hiding more secrets than these, including a few you'd never imagine. Lucky you—you get to spend a lifetime learning them all.

1. Everything we buy for ourselves—shoes, a skirt, even just stuff from the drugstore—really costs 20 percent more than we tell you it did.
Just because it's a classic sitcom plot doesn't mean it isn't true. "Sometimes I'll buy an outfit and charge half of it on our credit card and pay for the other half in cash so my husband doesn't know what I'm actually spending," admits one 32-year-old, who requested anonymity to protect her sneaky secret. Yeah, we know honesty is the best policy, hiding your spending habits is bad, blah blah blah. But sometimes we just don't want the hassle of arguing over the price of the fancy shampoo. Is that so wrong? We don't think so.

2. We actually think about sex—with you!—a lot.
Sometimes we think about it all day long. It's just that by the end of the day we're too damn tired to do anything about it. Now, if you could only catch us at lunchtime…

3. We're just as nervous about commitment as you are.
True, many girls grow up dreaming of Prince Charming, the white wedding, and happily ever after. But we're human, just like you, and when it comes down to the reality of tying our life to another person's, we get scared, too. "The idea of getting married completely freaked me out at first," says my friend Lisa, 34. "I know this sounds like a guy cliché, but I saw it as giving up my independence and being tied down." The good news is, once we're hitched, we're generally pretty delighted about it. Says Lisa, "Now that I am married, having a life commitment is so comforting and wonderful. I love knowing that we are a team and that we're going to be on the same team forever."

4. We may be modern and independent, but we still want you to be "the man."

We do want you to be sensitive, caring 21st-century males, but even the most ass-kicking, take-no-prisoners woman still wants to feel taken care of by her man somehow. Whether that means you take charge in bed, know how to fix the car and kill spiders, or even just carry the big suitcase when we're on vacation—when you act all manly, even if you're 98 pounds soaking wet, it makes us feel more feminine, more safe.

"I love that my friends and family always comment on how my husband opens the door for me and does all kinds of other chivalrous things—especially when I was pregnant, when he was so protective of me and my belly," says Lorraine, 29, of New Hartford, NY. "At the end of the day, being in his strong arms is definitely a good feeling, no matter how independent I know I am."

5. Our ex-boyfriends were not completely terrible in bed.
You know how we're always telling you things like, "No one does it like you do"? Um, yeah. Well, we may have been stretching the truth just a teensy bit. But we'll never actually tell you that a past lover was a bedroom dynamo—we're smarter than that. Just know that whatever toe-curling orgasms the other guy gave us, sex with you really is a million times better—because it's you, and you're the one we really want.

6. We're scared that we'll turn into our mothers.
We love our mothers, really. We admire them, we're grateful to them, we think they're the most amazing women on the planet. We just don't want to be them. That's why one of the worst insults you can hurl at a woman is, "You're acting just like your mother."

But here's one that's even worse: "You're acting just like my mother." It sends a horrible oedipal shiver down our spines—did he marry me because I'm like his mom? Will he start expecting me to cut the crusts off his PB&J? So please, if you value your sex life, never ever compare your wife to your mother. Out loud, anyway.

7. We want you to be jealous—but just a little bit.
We want you to notice—and care!—when the waiter flirts with us, or when other guys check us out on the street. It makes us feel that we matter to you. But please don't get all Neanderthal and possessive on us. "I'm very loyal, and if my guy can't understand that I would never do anything with anyone else, then that just makes me mad," says Paulina, 22, from Brooklyn. So, to recap: Raising your eyebrows when we introduce you to our cute coworker—good. Punching him out—very, very bad.

8. Yes, we fantasize about hot celebrity guys, but that doesn't mean we want you to be them.
Christian Bale is sexy and all, but can you imagine having to clean that Batcave?

9. We tell our girlfriends more than we admit to you (but less than you fear).
Yes, we tell them about the latest marital spat, complain about our mothers-in-law, and sigh over the hobby that sucks up all your free time. But we don't tell them how big your you-know-what is or that you cried in our arms when your dad died. Some things are just too important and intimate to share. "I definitely don't tell my girlfriends details like what my husband said when he proposed, the feeling I have every time I see him look at our daughter, and the little wonderful things he does for me every day," says Lorraine. "Those are just for me."

10. We really do notice and appreciate all the chores you do.
Why don't we say so often enough? Because we can't get over all the things you don't do. My husband, for example, is incredibly diligent about keeping a 6-by-10-foot carpeted patch of our apartment vacuumed and cat hair–free, and I love that. But it kills me that it never occurs to him to dust the furniture sitting on top of that piece of carpet, or to sweep the hardwood floor adjoining it.

Blame our lack of positive feedback on that stubborn female belief that there is Only One Right Way to do any given household task—our way. It's probably the real reason why men don't shoulder a greater share of housekeeping duties; we complain about how you did it wrong, so you never want to do it again. (Sounds familiar, right?) Let's make a deal: You promise to dust the lampshade (or wipe down the kitchen counter after you wash the dishes, or take out the garbage and then put a new liner in the can) once in a while, and we promise to sing your praises. Agreed?

11. We love you with all our hearts, but we still get wistful about the fact that we'll never feel that falling-in-love sizzle and spark again.
I'll just come right out and say it: Most women are love addicts. And while we appreciate the depth and richness of long-time love, there is simply nothing like the giddy, fluttery, crazy feeling we get (or rather, used to get) with a brand-new guy. We know we'll never feel that high again, and there's a little part of us that will always miss it. (Why do you think we watch so many romantic comedies?) But in the end, what we get instead—you, and a lifetime of true devotion—is more than worth the price.

Zon Rangsangan Lelaki Yang Wanita Patut Tahu

Ramai salah anggap kononnya zon erotik lelaki hanyalah zakar dan kepala zakar. Sebenarnya, banyak lokasi zon erotik ditubuh lelaki. Sebaiknya, semua zon erotik ini distimulasi secara lembut dan dilakukan apabila seseorang dalam keadaan tenang.

Stimulasi yang betul pada kawasan erotik ini akan memberi kenikmatan sama seperti stimulasi pada zakar, malah boleh mencapai orgasm. Kawasan erotik ini boleh distimulasi secara sendiri semasa masturbasi atau oleh pasangan ketika melakukan hubungan seksual.

Menurut lagenda Mesir purba Permaisuri Cleopatra merupakan seorang yang sangat mahir dan memahami tentang Zon Erotik Lelaki ini. Dalam hidup beliau, terkenal hubungan sulit dengan beberapa pembesar Negara pada waktu itu. Sentuhan Cleopatra disifatkan Gaius Julius Caesar sebagai sentuhan “ular yang berbisa”. Rayuan dan belaianya mampu merebahkan lelaki yang gagah kepangkuanya. Berbekal dengan kecantikanya yang di sifatkan sederhana dan pakej rayuan beserta sentuhan rangsangan. Menyebabkan pembesar-pembesar negara yang memusuhinya tersungkur dalam dakapan mesra …….

Sebagai infomasi anda saya petik kata-kata pakar tentang Zon Erotik Lelaki ini sebagai panduan suami isteri. 7 Zon Erotik Lelaki terletak pada :

1.Kerandut buah zakar
Kulit yang menyelaputi buah zakar adalah sensitif kepada sentuhan. Ia boleh diurut dengan pergerakan circular dengan menggunakan hujung jari atau secara oral.
Kerandut ini juga boleh ditarik secara lembut semasa seks oral. Buah zakar juga boleh distimulasi secara gentelan lembut dengan mengunakkan jari.

2. Puting dada.
Puting dada lelaki mempunyai kapasiti erotik sama seperti puting buah dada wanita. Ia kaya dengan bekalan saraf dan amat sensitif.

Pada kebanyakan lelaki, ia mempunyai kapasiti menegang dan menjadi keras bila dirangsang. Pergerakan circular yang lembut bermula dari arah luar ke dalam boleh dibuat di sekeliling puting. Lelaki juga akan terangsang apabila puting dipicit atau digentel.

3. Kawasan Perineum.
Kawasan perineum ini terletak antara zakar dan lubang dubur (anus). Ia boleh distimulasi dengan urutan perlahan dari pangkal kerandut zakar ke arah anus atau sebaliknya. Pergerakan secara sirkular dengan hujung jari atau secara oral di kawasan ini juga akan memberi sensasi erotik yang tinggi. Pergerakan yang sama juga boleh dilakukan pada bahagian peha sebelah dalam.

4. Kawasan ari-ari (suprapubik) .
Kawasan ini terletak antara pusat dan pangkal zakar. Ia amat sensitif kepada sentuhan dan urutan.

5. Kawasan punggung.
Kedua dua pipi punggung dan celah antaranya adalah kawasan erotik yang jarang diterokai. Gerakan jari secara perlahan dari hujung tulang belakang melalui celah punggung hingga ke anus. Lakukan ini secara berulang-ulang. Bahagian dalam pipi punggung juga boleh diusap lembut.

6. Kawasan Anus
Kawasan anus adalah zon erotik utama tetapi jarang diterokai. Anus boleh distimulasi dengan cara pergerakan sirkular dengan hujung jari atau oral di pembukaannya. Pergerakan ini boleh diselang-seli dengan stimulasi di kawasan perinuem, bahagian dalam peha dan pipi punggung.Jika seseorang itu lebih adventerous, jari boleh dimasukkan secara perlahan-lahan ke dalam anus.

Sebelum itu, pastikan jari dilubrikasi sepenuhnya dengan gel pelincir seperti KY Jelly. Pergerakan jari keluar masuk dan sirkular secara perlahan lahan mampu memberi kenikmatan pada seseorang lelaki.

7. Urutan Prostat.
Kelenjar prostat terletak di bahagian depan sebelah dalam anus. Ia boleh dirasa seperti satu bonjolan kecil. Kelenjar prostat ini boleh diurut secara perlahan dan hasilnya akan berlaku pengeluaran cecair jernih dari zakar.

Ini akan memberi kenikmatan pada setengah lelaki. Sebelum urutan ini dilakukan , jari perlulah dilubrikasikan dengan sempurna. Seseorang lelaki itu juga perlu berada dalam keadaan yang relaks dan selesa dengan proses urutan ini.

Saya harap dengan maklumat yang diberi ,ia dapat membantu anda dan pasangan berhubung zon erotik lelaki. Sudah semestinya dengan stimulasi zone erotik ini akan merangasang seorang lelaki melakukan persetubuhan yang hebat

Read more: http://ilhamnurulresources.blogspot.com/#ixzz1BG29Mium

Bieber Hospitalized

Pop singer Justin Bieber was rushed to the Providence St. Joseph's Hospital in California on Wednesday night when he experienced breathing problems after an allergic reaction.

Sources reporting to Life & Style magazine said the Baby singer was on the set on CSI: Crime Scene Investigation when he began struggling to breathe. No word yet what exactly went down but Bieber was later released from the hospital after doctors gave him the all clear sign.

The 16-year-old singing sensation was on the CSI set to reprise his role as the troubled teen, Jason McCann.

Apparently Bieber's allergic scare was not enough to keep him grounded, he'll be one of the scheduled presenters at this weekend's Golden Globe Awards show to be held in Hollywood. You can catch the show life on Astro's Star World.

The Social Network ; A story about the founders of the social-networking website, Facebook now on screen