Signal Sampling
Digital sampling is a simple concept, your taking wave of voltage information and giving it a high/low value so a 1 or 0 to map the signal into a waveform, higher the sampling more accurate the wave is to a point of 1:1 digital replica.
Detail level per each simple is defined by bit depth so 8-bit means 256 values of information per each sample thinkable in terms of steps of detail and 10-bit means 1024 values.
Bandwidth or sampling speed the amount of information an ADC can accept and convert to useful information is defined by sample rate in SPS or MSPS normally samples per second and million samples per second respectively.
1mhz = 2msps of minimum sampling so a 2:1 ratio
Less is worse more is better.
The best layman's example of this is HiFi 20hz to 20khz (Witch is around the average human hearing range) CD audio is digital 44.1khz just over 2:1 sampling, so 48khz covers the entire range of human speech, ware as 192khz would cover a large array of multiple sound information points like a orchestra.
- kHz is 1000hz
- mHz is a million Hz
- MSPS is a million samples per second
Oversampling is just the practice of capturing far more information than the potential of the source information, this just wastes space in simple terms and is always the preference to undersamping ware signal information is lost.
Four times the frequency of SC (sub-carrier).
The digital sampling rate of a composite video signal with respect to the sub-carrier frequency of an NTSC or PAL analogue video signal.
The 4fsc frequency sample rate is defined based off full spec composite
FPS: 29.97
14.31818182 MHz (4x 3.579545455 Mhz)
Full Signal Frame: 910x525
Active Picture Area: 720x486 & 720x480
FPS: 25
17.734475 MHz (4x 4.43361875 Mhz)
Full Signal Frame: 1135x625
Active Picture Area: 720x576
A subcarrier is a sideband of a radio frequency carrier wave, which is modulated to send additional information.
Examples include the provision of colour in a black and white television system or the provision of stereo in a monophonic radio broadcast. There is no physical difference between a carrier and a subcarrier; the "sub" implies that it has been derived from a carrier, which has been amplitude modulated by a steady signal and has a constant frequency relation to it.
In simple terms, lets say you have a 5mhz signal, inside this you have audio at 1.2mhz for left and 1.8mhz for right 2.2mhz has a timecode signal and 4.5mhz has the video signal all these signals are modulated
Some good real world examples are the HiFi carrier positions on common videotape formats.
Left 1.3Mhz / Right 1.7mhz
Left 1.5Mhz / Right 1.7Mhz
Left is 1.38Mhz A head & 1.53Mhz B head
Right is 1.68Mhz A head & 1.83Mhz B head
Exurbs From Digital Video and HD Algorithms and Interfaces 2nd Edition (By Charles Poynton 2012-02-07)
Pages 162 to 180
The following pages give a clear explanation of what 4fsc, S-Video, and Chroma Sampling are, witch are the core surface concepts to understand the processing chain of software tape decoding and how analogue is presented in the digital domain.
Four times the frequency of subcarrier, this is normally based off the composite signal standard for PAL/NTSC.
The 4fsc frequency sample rate is typically:
14.3 MHz (28.6 MSPS) in NTSC.
17.7 MHz (35.4 MSPS) in PAL.
In simple terms the same system used for D2/D3 tape.
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- FAQ - Frequently Asked Questions
- Diagram Breakdowns
- Visual-Comparisons
- VCR Reports / RF Tap Examples
- Download & Contribute Data
- Speed Testing
- Visual VBI Data Guide
- Closed Captioning
- Teletext
- WSS Wide - Screen Signalling
- VITC Timecode
- VITS Signals
- XDS Data (PBS)
- Video ID IEC 61880
- Vapoursynth TBC Median Stacking Guide
- Ruxpin-Decode & TV Teddy Tapes
- Tony's GNU Radio For Dummies Guide
- Tony's GNU Radio Scripts
- DomesDay Duplicator Utilities
- ld-decode Utilities