Time Base Corrector - a short primer (YT video)

[lordsmurf]

using an oscilloscope,

Which one do you have? I've been needing a new one for a while now, but just have not had time to research it. The problem is that the USB units are not ideal for VHS, and yet cheaper and more convenient (such as taking images like you just did). So what are you using, and what weaknesses and problems are you running into?

[Sharc]

using an oscilloscope,

Which one do you have? I've been needing a new one for a while now, but just have not had time to research it. The problem is that the USB units are not ideal for VHS, and yet cheaper and more convenient (such as taking images like you just did). So what are you using, and what weaknesses and problems are you running into?

This one from ANALOG DEVICES:
https://www.analog.com/en/resources/evaluation-hardware-and-software/evaluation-boards...ml#eb-overview
https://wiki.analog.com/university/tools/m2k

plus the BNC adapter board for convenience:
https://www.analog.com/en/resources/evaluation-hardware-and-software/evaluation-boards...2KBNC-EBZ.html
https://wiki.analog.com/university/tools/m2k/accessories/bnc

It's an oscilloscope, spectrum analyzer, logic analyzer, signal and function generator in one device. It connects to the PC via USB. Bandwidth, sampling rate etc. see the data sheet and manual. (I think you could download and install the user SW SCOPY to get an impression of the GUI)

Disadvantage: It has the disadvatage of every digital sampling scope. It reads analog signals in chunks (buffer by buffer), therefore it cannot record signals continually, there are gaps between the chunks. If this matters.

[Bwaak]

The pictures show one full scanline plus the next sync pulse indicating the start of the next scanline.

Thanks, @Sharc. These pictures clearly show that Panasonic's "VCR Refresh Copying" is not empty advertising.

Time Base Corrector (TBC) + 3D Digital Noise Reduction (DNR)
When connecting a VCR and DIGA to record VHS videotape images onto a DVD disc, the Time Base Corrector helps reduce jitter and performs signal conversion to create a stable signal. At the same time, 3D DNR detects and virtually eliminates randomly generated noise and color irregularities to help minimise flicker. Thanks to these two technologies, the tape input signal is automatically detected and optimum processing is performed to provide an easy way to even more beautiful digital recordings.

A handy picture from Digital Processing of Analog Television by Lior Zimet.

[dellsam34]

This one from ANALOG DEVICES:
https://www.analog.com/en/resources/evaluation-hardware-and-software/evaluation-boards...ml#eb-overview
https://wiki.analog.com/university/tools/m2k

How does it compare to the Rigol DS1074Z (1000Z series) which I bought few years ago for repair, Haven't used it on an actual video signal to check VCRs and TBCs, I know it does 1 Giga samples per second VS the one you linked which it does 100 mega samples per second, obviously because the Rigol is a full fledged scope that doesn't rely on the computer CPU. But what are other advantages of a USB scope over a stand alone one besides the price?

[Sharc]

..... but what are other advantages of a USB scope over a stand alone one besides the price?

If price doesn't matter ....eh? . There are affordable USB devices sampling at 1G samples per second as well, but why waste money for a 1G sampling scope for sampling VHS signals with a bandwidth of less than 5 MHz? A sampling rate of 10 MHz would be sufficient! (Shannon/Nyquist). The ADC resolution is another feature. The device I suggested uses a 12 bit ADC, other (affordable) models sampling at 1G have 8bit ADCs only. Look at the full picture - and what you get for the buck and for your actual needs. There are many choices.
The CPU load is usualy not a problem with USB devices. Sampling and storage (buffer) is done in the external device, the data are just transferred to the PC via USB and can be post processed (off line), similar video post processing.

[dellsam34]

I was under the impression that the samples per second is the smoothness of the graph and being high addresses the problem you described in the quote below:

Disadvantage: It has the disadvantage of every digital sampling scope. It reads analog signals in chunks (buffer by buffer), therefore it cannot record signals continually, there are gaps between the chunks. If this matters.

So what's the solution for the above problem then? I know one of the advantages of USB scopes is the large monitor of the computer, The scope I have has a screen of only 800x400, but I can always zoom in the waveform.

[lordsmurf]

@Sharc, thanks for your reply, but that's what I was afraid of.

@dellsam34, yep, lots of limitations with USB digital scopes. Cheap for a reason. But I don't want another brick on the desk, nor another boring box, nor something else aged. Digital scopes in general don't work well with VCR/TBC signals. So I often find it amusing when somebody tries to "prove" something, with a digital scope and VHS. Illustrate, maybe. Prove, no. 12voltvids has videos dedicated to this topic.

The pictures show one full scanline plus the next sync pulse indicating the start of the next scanline.

Thanks, @Sharc. These pictures clearly show that Panasonic's "VCR Refresh Copying" is not empty advertising..

I don't think that shows what you think it does.

[Sharc]

I was under the impression that the samples per second is the smoothness of the graph and being high addresses the problem you described in the quote below:

Disadvantage: It has the disadvantage of every digital sampling scope. It reads analog signals in chunks (buffer by buffer), therefore it cannot record signals continually, there are gaps between the chunks. If this matters.

So what's the solution for the above problem then? I know one of the advantages of USB scopes is the large monitor of the computer, The scope I have has a screen of only 800x400, but I can always zoom in the waveform.

What comes to my mind: Solution is using very large buffers to store the samples. The higher the sampling rate and the the ADC resolution the bigger the memory must be to store a certain duration of the signal (duration of signal x sampling rate x bit depth of the ADC). Gaps in the captured signal occur between flushing (reading out and transfer to PC) the full buffer and starting a new capture cycle. There are probably variants how this is actually done, something like sliding windows/leaking bucket principles or similar. The USB transfer rate will also be a limiting factor.
Or use an anlogue scope with analog integrating storage screen and various trigger and sync options (those legacy glaring Tektronix thingies, still good). It really depends what you want to do and what you expect and how much you are willing to spend for your purpose.

I am not advertising here anything. The small USB devices are portable and may be used with a notebook for basic service purposes, for example, including signal generation and logic analysers. There are devices for 20'000.- USD as well.

[Sharc]

@Sharc, thanks for your reply, but that's what I was afraid of ......
I don't think that shows what you think it does.

Don't think too much of what I might have been thinking

[lordsmurf]

@Sharc, thanks for your reply, but that's what I was afraid of
......
I don't think that shows what you think it does.

Don't think too much of what I might have been thinking

Oh you.

I tawt I taw a puddy tat.

[Bwaak]

A nice writeup about ADV7188, ADV7184, and ADV7180 chips. There are pretty pictures in it similar to the one posted by @Sharc. These chips have been discussed on this forum a while ago, I believe @jwillis84 posted about them.

[dellsam34]

The ADV7802 as well, In my TBS-800 thread I've demonstrated its capability to fix second gen dub baked in line timing errors by tracking, This appear to be mid to late 2010's chip, Here is an extract from the datasheet:

The ADV7802 implements a patented adaptive digital line length tracking (ADLLT) algorithm to track varying video line lengths from sources such as a VCR. ADLLT enables the ADV7802 to track and decode poor quality video sources (such as VCRs) and noisy sources (such as tuner outputs, VCR players, and camcorders). Frame TBC ensures stable clock synchronization between the decoder and the downstream devices. The SDP also contains both a luma transient improvement (LTI) and a chroma transient improvement (CTI) processor. This processor increases the edge rate on the luma and chroma transitions, resulting in a sharper video image.

[lordsmurf]

The ADV chips from ADI do not function the way some people (who have never used or dev'd with them) think they do. It tends to bake in errors, not correct. The default on-chip software from ADI is not usable as-is. This is why most devices using these chips has disable the "TBC" feature. Another loose use of the term, I'd add.