A primer on the picture and sound technology behind your television

No matter what your preference is in terms of brand or size, picture quality and sound quality are the two most important parameters for a good TV viewing experience. In this post, we will get an understanding on how to evaluate picture quality and sound quality of your TV.

Understanding Picture Quality

The quality of a picture is primarily determined by resolution, contrast ratio, refresh rate, picture engine, panel type and color depth (and viewing angle for some).

Resolution – how much data (number of pixels) is carried or shown in one frame, the greater the resolution the larger the data and hence a clearer picture. At an ideal viewing distance for a particular screen size, one shouldn’t be able to see individual pixels in a TV with a good resolution. It is important to check for pixel resolution especially around corners and edged objects on the screen.

VARIOUS RESOLUTION DEFINITIONS

Screen resolutions.png

IDEAL VIEWING DISTANCES

TVViewingDistances.png

Contrast ratio – the ratio of the brightest whites to darkest blacks. As shown below, the right side picture has a poor contrast.

Contrast ratio picture 1.png

A good contrast ratio will produce a bright image without lightening up the darks as shown below

Contrast ratio picture 2.png

Refresh rate Long back, somebody has discovered that if you run 24 pictures or frames per second (fps) then humans will perceive the act as a motion or a video. Therefore, refresh rate is how fast is the frame refreshed physically – it is the number of frames per second the TV can display – the higher it is, the more smoother and natural looking the motion of the video. Typically, you see 60 Hz (that’s 60 frames per second) and 120 Hz. Anything more is not required and not accurately described. These days all brands claim higher refresh rates by super-imposing frames or introducing blacks between two frames. These are artificial ways to improve refresh rates, but the native refresh rate is what one has to depend on while purchasing a TV. Check for blurs and noise around curves and edges before buying. While 120 Hz is a definite advantage over 60 Hz, most data sources are not beyond 60 Hz and hence 60 Hz is good enough. The advantage of 120 Hz comes in being able to play a 24 fps video smoothly.

Picture Engine – A picture engine is an image processing system that takes individual signals from various video output sources and throws an output onto the screen. Video processors typically include buffers, sequencers, colorizers, mixers and other linear and non-linear acts. They use various parallel computing technologies to enhance image and video production on digital devices such as TVs and Cameras. Since each manufacturer has its own ways of enhancing picture, there is no clear quantifiable way to rank a picture engine. Sony’s X-Reality picture engine is considered to be a state of the art picture engine. Similarly, there are top quality picture engines in other major brands such as Apple and Samsung. A recommendation to TV buyers is to watch out for the image processor and the picture engine in your TV before the purchase and check its performance online.

Panel Type – There are three major technologies used behind panel technology: ADS/TN (twisted nematic), VA (vertical alignment) and IPS (in-plane switching).

TN panels don’t provide great viewing experience, but however they provide high refresh rates (120 Hz) and high pixel response times required for gaming.

VA panels are the most common panels in LEDs and are often considered as a middle child between TN and IPS. VA panels have better viewing angles and dark blacks, however they sacrifice the response time (8 millisec) when compared with TN.

IPS panels have the best color reproduction, viewing angles and response time (4 millisec). While the earlier IPS technologies were slow in responsiveness and refresh rates, there has been significant improvement in recent IPS technologies with refresh rates of 120 Hz and 144 Hz.

VA Panel vs IPS Panel

Color depth – Color depth is the number of colors that a pixel can take. If a pixel is represented by 16 bits, then it will give you 65536 (2^16) colors.

24 Bit Colour: This format stores the Red, Green and Blue value for each pixel. Each of these can be one of 256 values, giving a total of 16,777,216 colours (256x256x256). Using 16 million colours allows for very photorealistic images, but increases the storage space requirements to three Bytes for each pixel.

32 Bit Colour: This format uses the same format as above for the Red, Green and Blue colours but also stores transparency information for each pixel. This allows each pixel to be one of 256 values from fully opaque to fully transparent. Because of the extra transparency information, the storage space for each pixel now requires four Bytes.

Viewing Angle – While may not be a very important attribute for Indian houses, a wide viewing angle complements to the experience. Some brands specially call out the 178 degree viewing angle.

Understanding Sound Quality

The quality of a good sound output is determined by output power, signal to noise ratio and frequency response (sound quality). If your TV box doesn’t describe these in detail, you can check the original manufacturer’s website to check these technical parameters in detail.

Output Power – Output power is the raw energy in your speakers and it is measured in watts. It is described as peak output or RMS. Peak output is the maximum energy output of the speaker for a short duration. Root Means Square (RMS) is the average output power over a long period of time. Usually, televisions in India come with 10W and 20W outputs. Typically, smaller TVs don’t come with decent speakers and therefore some people might want to augment the experience with a TV sound system.

Frequency Response – Humans can hear sounds ranging in frequency from 20Hz to 20K Hz. Below 310 Hz sounds are considered as bass frequencies, 310 Hz to 12 K Hz are mid-range frequencies that include human voice, piano, guitar and other instruments, 12K Hz to 20 K Hz are high frequencies that include high treble notes, high notes of human voice and some string instruments.

As you might’ve guessed, most speakers will give you the entire range. However the important parameter is: how does the speaker behave and how accurately is the sound reproduced at each of these frequencies? This is determined by frequency response. A sample frequency response chart is as below.

FrequencyResponseChart.png

It tells you what sound pressure level (decibel level) variations will your speaker have at each of the frequencies. Ideally, you would want a flat line across the range, but this is not possible for any speaker. Therefore, a good parameter to check is smooth transitions across the frequency range without any rugged highs and lows.

If a speaker specification only mentions the frequency range, then it is not helpful. You should always look for a specification such as 20 Hz to 18K Hz with +/- 3 dB. This will let you know that the sound pressure won’t drop beyond 3 dB across the frequency range.

While these specifications are not readily available with retailers, with little research on the internet or brand website you can find the detailed technical specifications for your TV or speaker that you are about to buy.

Hope this is useful, thank you.

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