Trying out a CCTV amplifier. It actually included a "DC barrel to bare wire" adapter cable even though that wasn't mentioned in the listing. But I'm currently powering it using 8x AA batteries in the hope that it's a less noisy power source, as suggested by Tony on Discord.
Here is another attempt at getting 8mm samples from the TEAC. Even with the amp cranked all the way, the card's level can be set to 31 without clipping. This weak, double-amplified signal may be too noisy to do anything with. But I figured it was worth posting so you guys can take a look.
I didn't touch the amp's HFGAIN adjustment, so I'm sure it's not set optimally.
VHS samples using the amp will be posted tomorrow or the following days.
+ Reply to Thread
Results 691 to 706 of 706
Last edited by Brad; 16th Jul 2021 at 08:57.(Formerly vaporeon800)
I adjusted the filtering quite a bit, bringing the bandpass filter further above the chroma signal, increasing bandwidth, reducing it, etc. Everything I did still shows the checkerboard pattern. Does this mean the issue is likely chroma oscillations present in the luma signal during recording of some of these tapes? My spectrum appears to be fine.
Also, while I was messing around with the filtering I sort of got Brad's Hi8 sample to decode. Luma is mostly correct, chroma is broken. I'm surprised this worked at all. There's definitely more post-demoulation bandwidth than VHS as I'm seeing sharper borders and a sharper image overall. And that's with the post-demodulation band limiting in place in the current code. I could not get Video8 to decode, however.
Last edited by Titan_91; 16th Jul 2021 at 20:27.
So, hopefully I can put this checkerboarding thing to rest as I may have isolated it. I have another tape I captured earlier on my Philips machine that did not show checkerboarding. So I tried that tape in the Sony and viola, no checkerboarding. I don't want to say the tapes themselves are the definitive cause, but they may be. It would certainly explain why I couldn't get rid of the effect on the Stuart Little tape if chroma noise is baked in to the luma signal at the time of duplication. There also seems to be less overall noise on the Arthur video. And while I was at it, I used this opportunity to compare sharpness between the 5MHz filter and 13MHz filter now that the checkerboarding wasn't getting in the way. Unsurprisingly, the 13MHz filter gives the best results.
Last edited by Titan_91; 17th Jul 2021 at 08:28.
Yeah the crosshatching does seem to be inherent or baked in (from insufficient separation) to some degree, just don't know how much exactly. At least for PAL on normal playback it seems to be a bit more visible with decks with EDIT mode on, so I assume the noise reduction or other post-filtering in VCRs do reduce it to a degree.
Hi8 is higher bandwidt than even SVHS so it ought to be a fair bit more detailed than a standard VHS capture. Additionally the format (and SVHS) has an extra (non-linear) emphasis/deemphasis step to further increase detail reproduction. Video8 and Hi8 has a slightly higher color carrier frequency on tape and did the phase rotation stuff a bit differently to VHS so will have to add that to make chroma work. (I think it just inverts rather than doeing 90 degree rotation but not sure.)
9954tony discord did a frequency sweep test on a cx card (one of the chinese modern ones with pcie connector and pci bridge chip and bnc connectors.) if anyone is curious about that:
The Arthur video has more bandwidth than some of my other tapes. Check out how low the luma sideband goes:
So I lowered the band pass filter cutoff from 2.6MHz to 2MHz to capture more of the lower sideband. This improved sharpness even further just a bit. Does using the -sl flag also do the same thing?
Yeah the current lower cutoff is a bit higher than ideal. Afaik in a VCR it's more like 1.5 mhz (not sure what order and type, and in B/W mode it will be lower) I think, so need to tinker with the filter makeup and demodulation to push lower without introducing white streaks on some samples. On most samples it's fine to lower it a bit though, as long as you don't get streaks or start picking up the chroma.
The -sl flag is a simple post-demodulation filter boosting some frequency bands so it's not the same.
Results with the 1.5MHz lower cutoff are pretty awesome! Attached is the 8-bit 40MSPS sample and two lossless MKV files, one interlaced and another deinterlaced with Yadif. Deinterlacing is the only thing I did. The result is so good using chroma gain of 1.7 and no sharpness level adjustment. Great color, contrast, and sharpness! Zcooger or VideoMem feel free to use this example in another YouTube video. We may want to merge the 1.5MHz adjustment in formats.py to the main branch at this point.
# Band-pass filter for Video rf. # TODO: Needs tweaking RFParams_NTSC_VHS["video_bpf_low"] = 1500000 RFParams_NTSC_VHS["video_bpf_high"] = 5300000
Last edited by Titan_91; 17th Jul 2021 at 20:52.
In my opinion that's below normal capture quality, You could get better results with a good VCR built in line TBC, I see a lot of jagged edges on those white window frames, I though the whole purpose of VHSdecode is to get rid of line timing jitter. Or was that your normal capture sample from normal video out such as composite?
That's all vhs-decode. My VCR outputs a softer image with no time base correction. Keep in mind too that VCRs perform noise reduction and other processing on the image such as artificial sharpening, which can also be done in software if desired. I just opted to forgo the noise reduction as it removes detail. As Chad Page said, once you're in the digital domain "Everything else is a solved problem." I'm eventually going to watch some of these software decodes on a CRT RGB monitor and see how it stacks up against a VCR with a normal composite output. The software comb filter alone is superior unless your TV has a fancy 3D comb filter.
In addition to this, many people believe the VHS format has no luma and chroma separation. We know this isn't true, and further limits the TV's ability to properly separate and decode the channels. This video is a good example. His close-up shots using a composite capture device have more noise and less definition than my results.
Last edited by Titan_91; 18th Jul 2021 at 12:57.
There is something on the chroma downconversion on which the documents are not very clear.
There is a mention on the JVC Video Technical Guide about the chroma carrier frequency being shifted 1/4 Fh (Horizontal frequency) between tracks/heads to avoid crosstalk.
It also mentions something about adding the last 4 chroma lines together to filter out the crosstalk component (or something alike).
The first issue is a fixed test on this https://github.com/VideoMem/ld-decode (with -cafc flag)
It also happens to show the crosshatch artifact more precisely on the reds of the Tom & Jerry sample.
And it can be seen at its strongest expression using the simpler ntsc1d chroma decoder.
The artifact is so clear that I think there's some processing to be done to eliminate it.
Also it seem to be something NTSC bounded.
For the ringing/ghosting part.
I guess there is some group delay between 2.5 ~ 3.7 Mhz on the baseband video that is not quite right, it need some kind of compensation.
BTW, there is an updated test run here:
Bear in mind, all of these are random samples from different VCRs using the flag parameters shown in each chart.
Most of them, are far from ideal and some could be multi generation and or LP tape copies.
There is still an issue with the sync when the pulses on the back porch have a glitch at the beginning (crafters sample).
On that sample the sync pulse doesn't go straight to sync level at the end of the line, it has one step intermediate level that might be confusing things.
Initial tests with the CCTV amp for VHS.
I recorded this segment on the Mitsubishi HS-HD2000U via S-Video. The source is a DVDR played on Philips DVDR3575H/37. (Actually, what I'm showing in this particular post is the player's own blue screen before the DVD started.)
The tape is played back on the Sony SLV-779HF, as usual.
In the images below, no amp with card level=31 always comes first. Followed by amp with card level=0 (again HFGAIN not tweaked).
I don't see checkerboarding in the "no amp" decode, but I certainly do when it's added. What do we make of that?(Formerly vaporeon800)
This is caused by a reflection above the RF envelope. Like before, the chroma signal of the reflection (second harmonic) is protruding down into the bandwidth space used for luma. This shows up as a line right above the brightest trace. The brightest trace is your FM envelope for the luma signal. For me, this does not happen if I use 50 ohm mini coax cable, a 50 ohm BNC terminator, and 50 ohm BNC connectors on my VCR and my capture card (which someone modified for me). But that requires soldering and a bit more work.
If I look carefully, the reflections are there originally but they are only amplified in this case along with the main signal. The first screenshot also shows checkerboarding as well but it's very faint.
Does anyone in the US want this Philips VCR I've already modified with a BNC connector? I'll include a BNC to RCA plug as well. I don't need two modified machines.
Last edited by Titan_91; 20th Jul 2021 at 15:27.
Boost or calibration, need to check if the burst amplitude matches specs.