Resolution, audio sampling when digitizing tapes?

[heychrischin]

A couple quick questions while I wait for digitizing hardware to be delivered:

* Many of the recordings I will be digitizing were done on an old VHS camcorder (I believe it was an RCA brand). Was there the equivalent of a “sample rate” for audio on those devices? If so, what would it be?

* After reading "Guide to Understanding Video Sources, Part 2 – Capturing Videotapes", I want to make sure of something. Since the media was recorded on an old VHS camcorder, I should import at 352x480, correct? The fact that I’m using S-Video out from an S-VHS play doesn’t make a difference, is that right?

[jarecki83]

You can't determine sample rate in analog recordings, for best quality you should capture audio at 48000 Hz.

For best picture quality you should capture video at 720x480 resolution using S-Video.

[Gary34]

That guide has a lot of good information but it is old. People don’t really go straight to DVD now because hard drive space is really cheap now compared to what it was. Now everyone captures to a lossless codec. Someone would capture with 352 by 480 if they were going straight to DVD with an ATI AIW card. Some DVD encoders have trouble with 352 by 480. Anyways going lossless prevents loss when editing. Capturing 720 by 480 using Huffy is recommended now. Then you encode to a lossy codec like H.264 (MP4 container) at the end because it’s a delivery codec. You keep your captures lossless during editing then encode to w/e you want at the end.

S-video separates your chroma and your luma. You get a lot less noise like that. It’s a very noticeable difference. If you put them both on a vectroscope you can see the composite one going all over the place and S-video looks very tame by comparison. Composite will have rainbow affects and a lot of other issues you don’t want.

[traal]

Roughly, Nyquist says sample rate should be at least 2x the highest source frequency. Since VHS has a ~15kHz audio frequency response, the audio should be sampled at 30,000 Hz or better.

S-VHS has 420 lines per picture height which is about 560 pixels across, so 352 isn't enough horizontal resolution. Try 720x480.

[latreche34]

Capturing video is 720x480 (576 PAL/SECAM) and audio is 48Khz/16bit (24bit certain pro equipement), These are the native sampling rates for video and audio of any capture card locked by hardware, You don't have any choice of choosing otherwise, Any setting change in the capture software is a simple conversion on the fly in the software domain from the native sampling to the suggested sampling rates, And you know conversion always incur a loss. Back in the day people were converting to lower resolutions or encoding on the fly to save disc space, this is no longer the case, so take whatever the capture card is spitting out, your valuable memories are worth it.

[Gary34]

I’ve seen this conversation before. https://www.digitalfaq.com/forum/vid...s-720x480.html
I was just thinking that might be what is confusing him on that page of the guide. https://www.digitalfaq.com/guides/vi...nd-sources.htm

[lordsmurf]

352x480 is/was more for MPEG capturing, which was the big thing when that guide was written. I need to update it again. Lossless capturing generally requires Full D1 specs, 720x480, so do that.

Sometimes math is art, and Nyquist is a good example of it. It's more theory than practice. The numbers are overall too high, ridiculous even. That's because too many variables exist. Nyquist, as applied to VHS, is in a vacuum of unrealistic perfection. Sure, look at it, understand it, but don't follow it too closely.

In the 2020s, capture lossless Huffyuv, 720x480, interlaced.

Capture audio 48 kHz. No more, no less.

[dpalomaki]

Worth noting that VHS (and Video8) has a nominal horizontal resolution (B&W) of about 240 lines (per picture height), so 352x480 was a minimal generally acceptable level for plain old VHS recording sources. Off-the-air and cable broadcast signals were more like 330 lines so 352x480 would be very marginal at best for them (depending of the original source material). S-VHS recordings had the potential for ~420 lines as discussed above. SD DV recordings sources have the potential for ~500 lines, which 720x480 can generally handle. Of course the recording will be limited by the source (camera head, off-air, etc.) as well. Playing a VHS recording on a S-VHS machine may look better only because the S-VHS machine electronics are designed pass a better signal and should have fewer internal losses as well as usually avoiding composite output.

Keep in mind that video lines horizontal resolution is is based on the number that can just be distinguished by eye on a good monitor. It is akin to the -20 dB point in audio frequency response. Vertical resolution is limited on the number of scan lines (as well as the source material including camera head).

The quality of the final captured image cannot exceed the original source or the weakest link in the chain. However, some tools may process the image to create detail that was not present in the signal as it reached the capture device.

[lordsmurf]

Quote:

Originally Posted by dpalomaki

Worth noting that VHS (and Video8) has a nominal horizontal resolution (B&W) of about 240 lines (per picture height),

It must always be mentioned that "240 lines" analog is NOT the same as "x240" digital resolution.

I've always hated that 1990s myth, from the era of VCDs (which were a really low 352x240 MPEG-1).

VHS is approximate to 250-300 x480 interlaced, and the theoretical maximum (a perfection which doesn't exist) is about 336x480.

[latreche34]

In early 80's a group of radio telecommunication engineers call themselves CCIR, an international organization known now as ITU-R got together and discussed this matter on how to digitize analog video, After numerous studies and debates and math crunching they decided that 720 will be the ideal sampling rate for a video scan line taking into considerations different video formats and standards that were available back then, In 1982 they finalized the standard by defining how the color portion of the video signal is going to be encoded into the luma, The color encoding system is known today as YCbCr 4:2:2 rec.601.

Here we are in 2024 still talking about this matter.

[captainvic]

Just curious... is it possible to capture 24 bit audio on video captures using VirtualDub as the capture software? (I don't think VirtualDub has a 24 bit audio option, correct?)

[latreche34]

Vdub captures whatever the card supports, it's your capture card hardware that makes that choice, Most consumer hardware are 16bit, I have never heard of 24bit audio on a consumer capture card, I could be wrong, but unless you are doing some serious audio restoration 16bit is more than enough.

[vwestlife]

You can capture 24-bit or even 32-bit audio if you want, but it will do nothing except waste disk space. VHS Hi-Fi is theoretically capable of CD-quality (16-bit) audio, but in reality head switching noise and the inherent noise floor of the recording and playback circuitry means that even 12-bit DV audio is perfectly capable of sounding indistinguishable from the source. Heck, Sony had an 8-bit PCM digital audio system on Video8 tape, with some extra quantization trickery to achieve the equivalent of 10-bit audio, and that sounded great too.

[lordsmurf]

Quote:

Originally Posted by latreche34

Vdub captures whatever the card supports, it's your capture card hardware that makes that choice, Most consumer hardware are 16bit, I have never heard of 24bit audio on a consumer capture card, I could be wrong, but unless you are doing some serious audio restoration 16bit is more than enough.

A lot of consumer cards measurebate, try to one-up the competition. But it's just numbers, not actual quality improvements. In most cases, cheap 24-bit cards are worse than quality 16-bit, and both can be consumer. It's a game manufacturers play to get money from sheeple, those that are easily impressed by "bigger numbers".

[Haunted_TBC]

Isn’t that why the Santa Cruz destroys nearly every 24 bit sound card that isn’t a Digigram despite being only 18-bit?

[dpalomaki]

A lot was driven by broadcast standards such as signal bandwidth, and the state of the art for generally affordable consumer gear; i.e., a trade off between cost and quality. The on-the-air video + audio signal was limited to 6 mHz bandwidth. So Beta, Video8 and VHS (the consumer formats) were designed to provide an image that would be acceptable to most viewers on available TV sets of the time when playing a first generation recording off the air or live camera. The bandwidth limitations of the analog formats (i.e., frequency response, especially color information) resulted in second generation copies that were not very good. (But that was OK with the copyright owners.)

Keep in mind that a 24-bit copy of 16 bit material can retain the original 16-bit quality (no more). The remaining 8 bits are largely "wasted" except perhaps as a way to mitigate round-off/truncation errors during processing (and gobble up processing power and storage space). I suspect some AI processing schemes may impute detail missing from the original recording but that ceases to be the original recording, it now is a variation on live action-animation which may or may not be what one is seeking. After all video is an art form.

And a lot also depends on how well the A/D and D/A are implemented in hardware and software.