Monday, July 28, 2014

How about some EQ Part 1 of 2?

Today I am going to shift some things up...

Rather than keep on the video path, I wanted to get something out there that comes from my studio background.

I want to talk about EQ.

So the biggest question I would bet is "What is EQ?"

EQ is an abbreviation of equalizer, or equalization.
It is a frequency based effect where you can amplify, or attenuate specific frequencies based on a series of controls.  Some might call it frequency specific amplification.

Where did it come from?

EQ, like much of what we now deal with in the audio world, came from the telephone world.  Way back in the olde skoole days, phone audio was driven across many many miles of copper wires.  Copper has some nifty intrinsic values to it inclusive of the fact that it has some signal loss, so in order to counter the signal loss, an amplifier would have to be added periodically into a signal chain in order to drive the signal further at the same level.  However, this loss was not equal across all frequencies, so the amplifier had to also have different gain levels based on frequency information.  So what did they do?  They turned up one set of frequencies more than the next, and more than the next, giving what could be called frequency specific amplification.  The net result is that the signal was equalized across the frequency ranges by this frequency specific amplifier.  Thus was born the Equalizer (EQ).

There are a few key terms to note in your quest to understand EQ.
Those terms are
Frequency, Bandwidth, Q, and Gain...

What do those terms mean?
Frequency is defined as the rate at which something occurs or is repeated over a particular period of time, or in a given sample...   Thanks google...  What does frequency mean as it pertains to EQ?  In this case, the easiest translation of frequency is pitch...  But in reality frequency is the cycles per second (measured in Hertz, abbreviated as Hz) of the signal you are trying to affect.

Gain - This is defined as "a measure of the ability of a circuit to increase the power or amplitude of signal from the input to the output by adding energy converted from some power supply to the signal."  That's from Wikipedia...  But as it pertains to what it means to you, is how much louder or how much quieter you will/can make it...  This is usually measured in Decibels... or abbreviated as dB.  If you would like an in depth discussion on dB's, I will probably do that later.

Bandwidth and Q are the sticky wicket.
Several people will tell you they are the same as each other, but they are NOT.  They are inverses of each other.  So a high bandwidth means a low Q, and a Low Bandwidth means a High Q.  So what does it actually mean?  In an EQ this refers to the range of frequencies affected by your gain.

Tying them all together...
you would select a center frequency, if it's available, you would select the bandwidth, and then you would turn it up or down with the gain knob/slider...

What kind of EQ's are out there?

There are all sorts of different styles of EQ's, some used more than others, but the three biggest that I would suggest are used would be a Graphic EQ, a Parametric EQ, and a Semi Parametric EQ.
A graphic eq is one that typically has fixed frequencies, typically fixed bandwidth/Q, and variable Gain...  Often times you will find them in 31 bands, but they could be in all different sizes...  The picture here shows a dual channel 31 band Graphic EQ.


You simply select which frequency you want to affect, and turn it up (because in music production we never turn things down right?).  Alright you also will want to turn some of it down.


How does this differ from the parametric families...
Well the parametric families typically have fewer bands to affect, but you then add the ability to control what frequency you would like to affect.  In addition to that they also have the ability to alter bandwidth...  a typical parametric equalizer would have 4 bands, and







You can see here the top knob is for gain, the middle knob is for bandwidth, and the bottom knob is for frequency.  This is a Manley Massive Passive EQ...
You may also notice that there are a few switches on top.  These aren't completely common, but they aren't uncommon either...
The first one says Boost/Out/Cut...  This is unique to this EQ relatively speaking, where you have to decide whether the gain knob is boosting or cutting, but the OUT part is not.  This is what I refer to as the sanity check.   What this does is allows us to hear the changes we are making...  So we can make a change, then switch that to out, and remove the change to make sure we are affecting what we think we are affecting.
The second one says shelf/bell...  This is an interesting thing.
A bell is what would result in a graph of the frequency response of a parametric EQ... It would look like a bell curve on a graph of frequency response...  The bell setting will affect the center frequency the most, and then less and less towards the edge of your frequency range based on your bandwidth selection...  So if you selected 1000Hz as your frequency range, and a 200 Hz Range, you would affect 1000Hz the most, and 1100Hz and 900Hz the least (as an example of easy math).
The Shelf is that whatever frequency you selected, and all frequencies above that (or below that) will be affected the same...  So a shelf is applied to 100 Hz, and you turn it up by 10dB...  All frequencies 100 Hz and Below will be turned up by 10dB...   If you look you can see the wishbone looking things next to the middle knobs...  Those are the shelves...  You can see the first two on the left affect the low frequencies, and the two on the right affect high frequencies...


So what's the difference between a Parametric, and a semi-Parametric EQ?
A parametric EQ is described above, a semi-Parametric typically will remove one or more controls.  So a common semi-parametric will allow for frequency selection, but you cannot control bandwidth.  Or you may have 2 fully parametric bands, and 2 semi parametric bands on the low and highs, and the resultant EQ BOX would be called a semi parametric EQ.  See the picture below.




You can see on this example that this is a 2 channel semi-parametric EQ.  The mid frequencies on each channel have the Q adjustment, but the low and high frequencies on each channel do not...


So this is all well and good, but what do I do with this stuff?

Well that's the discussion for part 2.

Let me know about the types of EQ and brands are your favorite...  Maybe you love the mackie EQ's, maybe you have an OLDE SKOOLE stand by favorite...  My first EQ that I purchased was a dual channel Alesis MEQ230 - total piece of junk but it was mine, and I loved it.

Send me your comments on your EQ experience too!

Tuesday, July 22, 2014

Chroma Subsampling

Last week I started off with the 4K image of my backside...

I am going to go a bit further into the rabbit hole...

One of my biggest objections to the whole 4K thing comes from this topic of chroma sub sampling...

The whole idea of it is that we as humans stink at seeing colors, but can determine brightness quite well.  That is to say in more technical speak, we can determine luminance information much better than we can determine chrominance information.  Because of this fact, we have figured out that if we create an image with a certain resolution for the luminance side of the world, we can decrease resolution in the chrominance side of the world, and still have a relatively good experience.

I know several of you right now are saying that color is just as importance as brightness, but I would tell you that for the most part you may be inaccurate.  There are several standards out there right now that use chroma sub sampling and have taken off like wildfire.  One standard that has used chroma subsampling is DVD Video, but that's small potatoes to the largest... which is Blu Ray.

That's right the Blu Ray video spec calls for chroma subsampling.
You have not watched a movie on DVD or Blu Ray that is full bandwidth ever.
So the amazing visuals you thought you were seeing are NOT all that great.  They could be made better.

Blu Ray (and DVD incidentally) uses what is called 4:2:0 chroma sub sampling...
What is this 4:2:0?

The first number represents the horizontal Sampling reference
The second number represents the number of chrominance samples in the first row of J pixels
The Third number  is the number of chrominance samples in the second row.

For your convenience, A nifty Chart:
4:1:1     4:2:0     4:2:2     4:4:4     4:4:0
Y'CrCb
=====
Y'                                                            
+++++
1234 J = 41234 J = 41234 J = 41234 J = 41234 J = 4
(Cr, Cb)1 a = 112 a = 212 a = 21234 a = 41234 a = 4
1 b = 1 b = 012 b = 21234 b = 4 b = 0
¼ horizontal resolution,
full vertical resolution
½ horizontal resolution,
½ vertical resolution
½ horizontal resolution,
full vertical resolution
full horizontal resolution,
full vertical resolution
full horizontal resolution,
½ vertical resolution


So as you noticed, the full resolution is noticed as 4:4:4...  You will also notice that our amazingly awesome 1080p video from blu rays, is actually 1/2 resolution vertical, and 1/2 resolution horizontal.
Via the Magic of Math, you get 1/4 the resolution as the 4:4:4 chroma subsampling.

You are literally using a full resolution black and white image in combination with a 1/4 resolution color differential image to get the resultant image...

So you have never seen a full resolution image from a blu ray (or a DVD player for that matter).

Now how does this relate to may backside, and 4k?  well hopefully you still don't want to see a 4K resolution image of my backside, but as it pertains to 4K, it comes down to bandwidth...

The Math of figuring out bandwidth required for signal rates isn't quite as easy as it might seem as there are plenty of factors out there that would seem like nonsense, but when you get down to the nitty gritty, it makes perfect sense.   If you would like to see the math, let me know and I will do it out for you.

The end results are:

4:4:4 1080p 60 Frames per Second data rate, with 8 bit color depth, and our bandwidth is 4.46 Gbit/s
4k Video (which is essentially 4x 1080p) at all the same stipulated factors requires bandwidth of

17.84 Gbit/s!!!!!!

Our current HDMI 1.4 spec limits us to a max data rate of 10.2 Gbit/s...

Hopefully most if not all of you could agree that 17.84 is greater than 10.2...

So how do them TV folks tell us that 4k is actually happening...  They do it by chroma subsampling...  If they only include 1/4 of the color information, you can get a passable 4K signal...

The result is that the 4K video at 60 Frames per Second with 8 bit color depth and 4:2:0 chroma subsampling weighs in at about 9 Gbit/s...  Less than the 10.2 limit.

So again, it all comes back down to this...
4K in full resolution simply does not exist for the masses yet...

Let me know what you think about the proliferation of less than full resolution color sampling...



Oh, yeah, and apparently our eyes are terrible at determining color resolution.

original                             Luminance                      Chrominance













Monday, July 14, 2014

4K my Backside

As the title of the post suggests...   4k resolution of my backside... There's a lovely image...

If you aren't sure about what 4k is - 4k is the name given to the resolution (really set of resolutions, but who's counting) that is double 1080p resolution.  So 1080p resolution is 1920 pixels by 1080 pixels...  With a little Math Skills, 4K resolution doubles that, so it is 3840 pixels by 2160 pixels...

That's impressive...  To think that we went from commercially viable 480i standard definition to this 4K resolution in 15 years or so...  What happened in the previous 15 years of broadcast...  Well not too much of note about resolution, that's for sure...

But really I don't get it.

I just got back from a large conference called Infocomm where all the buzz was about 4k resolution, and how everything had to be 4k resolution.
Truth be told, NOTHING was full 4k resolution...
The simple fact is that there is no real transport available yet to allow you to connect one thing to another and view things in 4K resolution.  So it begs the question, what's the deal?

If we look at Apple's version of what they call "Retina Display", we can notice some stuff...  For those of you not familiar with what a "retina display" is, it is defined as

"a brand name used by Apple for screens that have a pixel density high enough that the human eye is unable to discern individual pixels at a typical viewing distance." - Wikipedia

So I start to wonder.  My assumption is that since we as a society are buying this "retina display" technology based on how many ipads etc are being sold, that we must accept at some level the research behind the "retina display".  But what are the resolutions and distances associated with these displays...

Here's a convenient chart courtesy of Wikipedia...


Model[7][8][9][10]PPI (pixels perinch)PPCM (pixels percm)PPD (pixels per degree)ResolutionTotal PixelsTypical viewing distance (in/cm)
iPhone 4/4S and iPod Touch (4th generation)32612857960×640614,40010 inches (25 cm)
iPhone 5/5C/5S and iPod Touch (5th generation)1136×640727,040
iPad (3rd/4th generation/iPad Air)264105692048×15363,145,72815 inches (38 cm)
iPad Mini (2nd generation)326128852048×15363,145,72815 inches (38 cm)
MacBook Pro (3rd generation) 15"22087772880×18005,184,00020 inches (51 cm)
MacBook Pro (3rd generation) 13"22789792560×16004,096,00020 inches (51 cm)



well that's great...  So what gives...  most of these resolutions are greater than 1080p...  But if you will notice most of these distances are pretty small.   I sit here on my mac book pro and I realize I am about 20" away.  I cannot discern pixels...

But what the heck does it matter once you get further away?

If I cannot discern it at 20" how am I even going to begin to try to discern it at 60" or 10' for that matter...

I bring this up to point out how pointless this whole resolution thing is...  at a 4k resolution how big does the display have to be, and how far away do you have to sit in order to start to discern pixels...

Well quick math would show us again that we have to be greater than 220 or so pixels per square inch at approximately 2.5x the height of the display will be the distance.

take a 50" display...  This is 24.5" tall, so at about 61.25" we need there to be more than 220 pixels per square inch to exceed the retina display standard...  What I can tell you is that if you have a 50" display, and you are viewing it at 5 feet away, you have a very small apartment, or you are sitting too close to your display...

There are about 1070 square inches in the 50" display...  There are 8,294,400 pixels in a 4K display... the pixel density FAR exceeds apples retina display...

The math almost doesn't matter because reality sets in..  You would put your nifty 4k display on teh wall, and sit 10 feet away, so there's no WAY you could discern pixels at that distance...  if you want me to do the math out to see that end of the spectrum, let me know, and I will show it...  But the end result is that this 4k thing is being hyped for the sake of being hyped right now...

So based on Apple's Math, we have gone far past the limit of our eye's ability to notice pixels...

Moreover, what sources are out there?
Really the only truly viable sources could be a streaming service, such as Netflix with ethernet connected directly to the display(which is a compressed format), a Red ray player (who actually has one of those yet), and MAYBE a Macbook pro (that's not actually 4k yet), or other such advanced computer where the resolution would exceed 1080p by a good amount but not be at 4k yet...  In short there really isn't any sources yet either...

So let me get this straight.
We Hype 4k for our living room, to hang it on the wall 10 feet away where the pixel pitch far exceeds our ability to see pixels, to have no sources, that even if we did have sources, we couldn't actually see them because we have no way of plugging these things in yet...

So I just simply don't get it...

What I will say is that the 4K revolution is in the wrong place...
There is a place for proper 4K, and when the HDMI 2.0 spec comes out and there is a viable transport (current HDMI cables cannot handle 4K bandwidth, but HDMI 2.0 will be able to (in theory)).  There will be a great home for 4k technology...

For instance in the field of medicine, such as surgical field displays...  Having those in 4K could save a life...  Or in oncology, having a 4K resolution Xray or other diagnostic scan might pick out something a 1080p might not, again, potentially saving people's lives

LARGE FORMAT DISPLAYS...  Those will be able to benefit from 4K resolution... For instance take all those numbers I just blabbed at you, and make it a 100" display.   THEN it makes sense to have 4K resolution...

The net result is that I can see 4K coming
But for now...  I'm pretty sure it's just a bunch of hoo-ha that's supposed to make you buy a new TV
To quote Public enemy for a moment...

Don't Believe the Hype...

Let me know what you think about 4k, and the viability of the 4K resolution today...