Spaced Ranger

You_Too said:

... it started with one curve and ended up being 5 curve files, 2 histogram conversions and lots of other settings like "selective color". I revisited the settings about 30 times or more during that time.

Im-m-mpresive!

And I read mention of this one group of settings will process the complete movie (without further intervention), too? I do hope more operation details will be forthcoming as time permits. Don't forget lots of pictures.  :)

@ frank678

Was that any better? :D

You_Too said:

... we're way past the repair/color correction state.

Great! (I thought your example picture was it's present state.)

Have you described your processes for the fix-ups?
I scanned through the thread (unsuccessfully looking for that GOUT snapshot unsaturated) and didn't see fix-up procedure descriptions.
(Techniques are of particular interest to me -- like snicker's approach, to which I was beginning to explore before coming across it).

If not, please do! I also like lots of comparative pictures and clips ... as you may guess by now. :)

Thanks!
And here's the point I was making:

Today's color film is R-G-B and it has a sort of built-in compression with resulting "compression artifacts" -- that is, omitting colors from the greater range our eyes can see:

After that, anything that's been captured into the digital media is also compressed with it's own compression artifacts -- sub-sampling (4:4:4, 4:2:2, 4:1:1, etc.) and redundancy elimination (mpeg, et al). Media distribution compresses that even more due to space, cost, and technology constraints. So the media mush we end up playing with is pretty pitiful (fortunately, things are getting better and cheaper). The closer we stay to the original film, the better off we are.

In dealing with fixing up the inherent faults, color-space conventions that are useful within limits. The previously mentioned HSL is common and is intuitive. But it is only a representation that works best in small adjustments. When pushed beyond that usage, it produces effects that are actually misrepresentations.

Using HSL to analyze a picture, when saturation is max'ed, ...

reveals "damage". (Interesting that this looks allot like over-compression flattening.) But, those RGB numbers compared to the non-saturated picture ...

shows that increasing the saturation changed the proportions between the components of RGB to create a false impression of the type of picture damage (missing chroma rather than flattened color).

snicker demonstrated that "impossible" fixes could be made in RGB because "damage" in one or more of the parallel RGB channels could be patched with better condition parts from the others channels. (He was working on "crushed" or "blown-out" channels to recover detail, but any problem in between is likewise addressable.)

Anyway, from the RGB perspective, a fix might not be worth the effort. My quick tweak of the original picture's RGB gammas produced a nice color correction/adjustment without a hint of the "max'ed saturation damage":

I thought it might help with fixing the "hopelessly damaged" where it mattered.

To mis-quote a certain dark helmet ...

"Don't be too proud of this HSL representation you're using. The ability to over-saturate a picture is insignificant next to the power of RGB."

;)

[BTW, I just tuned into this thread and it's looks awesome.]

You_Too said:

The GOUT has unfortunately been desaturated even after the scanning. In lots of scenes there are parts of the picture which actually has no color information left at all.

Without finding that frame (non-saturated) to examine it's problem in R-G-B before asking this, I'll just ask ...

Did you ever look into snicker's (excellent) concept of "repairing" clipped luminance (both high & low) by patching in non-clipped (or lesser clipped) same-areas from different R-G-B planes?
http://originaltrilogy.com/forum/topic.cfm/Harmys-THE-EMPIRE-STRIKES-BACK-Despecialized-Edition-HD-DVD9-AVCHD-and-SD-NTSC-DVD5-AVAILABLE-NOW-Read-1st-post/topic/12511/page/28/
Maybe useful in such instances?

On the software side of these things ...

Do any include useful software that will do simplistic edits (trims and splits) of a capture and create Blu-ray formatted DVDs for viewing (without re-encoding video/audio) and, just as important, extract and rejoin the disc-saved splits back into the full capture?

If none from them, are there such programs (preferably free or cheap) that you know will do all the above?

You_Too said:

Unfortunately there is no way to bring all colors back since the GOUT is sourced from a faded interpositive.

Technically, yes. But practically speaking, if you know for what you're aiming, mild fading shouldn't present much of a problem, as demonstrated in this more severe (?) fade before-and-after:

THX 1138 preservations (Italian Cut available, see 1st post) - 53 and the 5 preceding pages.

Looking forward to lots of projects samples (comparison snapshots / clips) and detailed descriptions of techniques used. And please give consideration to those of us who must DL the old fashioned way.  :)

Histogram adjustments do take some learning, mostly by seeing what-does-what. That's why it's best to experiment in a paint program because you see the graphs and the result-overlays and the eye-dropper values -- which all help develop intuitive operation. And it's probably better to stay with the controls-histogram than adjusting graph-points directly.

Your clips show you're on the track. Normally with that green-tinge, I'd say to gamma-down the GREEN channel. But if you're putting points on the graph, you must slide down each point in proportion to what a gamma curve would do (tedious and prone to errors).

Trying to see how easy it would be using the 2006 DVD release as a target, I discovered my standard easy-approach wasn't doing the job -- get one color right and other colors go wrong. I'd say this is Lucas Film's doing things like selective-area tinkering. That makes for more complex work.

So, I used the 2006 DVD only as a guide and adjusted the luminance first to match the range (does wonders for the picture) ...

and then corrected the saturation and hue for matching skin colors (ignoring what happens to other colors) ...

and that's it. The results actually look quite good across dissimilar shots. You can probably use this one setting for the entire movie (if such adjustments are readily available in VirtualDub):

                  VHS CAPTURE                                  ADJUSTMENT                                        2006 DVD

Interesting to note that those other colors look quite natural against GL's post-production/release ceaseless tinkering to change the environment. *sigh* :)

BTW, if you can do that GREEN channel gamma, this would be your result (and better than my attempt, I might add):

                                VHS FILTERED                                                       + GREEN GAMMA=0.87

@ SilverWook

Please do keep us appraised of your progress. But just a reminder ... "This is no place for prayer. If you want to speak to OMM you must go to a unichapel, you know that."

@ msycamore

That's an excellent link -- Back to the Future with THX 1138 (10/04). I remember coming across it sometime back. With "Some of it is dailies outtakes, 16mm footage, some it was original negative...", something is clearly going on. Anyway, good to read that you're making available the various sources.

digitalfreaknyc said:

 

... Otherwise, you can get the Hauppauge.

 

To quote Tony Stark: "Is it too much to ask for both?" :)

Can the Colossus handle all the audio encodings? I don't exactly know what all is. I see it supports DD5.1. But what about TrueHD or DTS or DTS-HD or anything-else, recordable from everywhere-else? Or is that to much to ask for now?

Anyway, it looks great as a fast & simple hi-def digital VCR.

I can also see the 1080p30/24 ones more useful for in-computer captures (video games, et al) -- although more complicated due to the separate audio recording and subsequent syncing / remuxing.

I thought "flashscan" was a classification, not a product. 8mm / 16mm / 35mm? No focus or sprocket claws? 4:4:4? 2K capture? Optical audio scan-conversion(!)?
I THINK I'M IN LOVE!! :D

http://www.flashscan8.us/

But, ouch, the cost. It's either get a job in the socialist-Obama regime (trillion$ up for grabs) or wait for MovieStuff's Retro. :)

@ Harmy

THX11384EB ... what he said. :D

@ poita

That is cool! Brief details on your system, please, and any research you used in selecting/building one!

@ SilverWook

You remember this from earlier; pictured here (towards the middle):
http://originaltrilogy.com/forum/topic.cfm/THX-1138-preservations-Italian-Cut-available-see-1st-post/post/585765/#TopicPost585765
and dated here:
http://originaltrilogy.com/forum/topic.cfm/THX-1138-preservations-Italian-Cut-available-see-1st-post/post/585909/#TopicPost585909
Recorded on VHS tape, with "coily", but missing the "lost scene". Too bad ... "GL was here".

@ msycamore

The source is the question. George Lucas complained that his Star Wars original was falling apart (let's just play along with that claim for now) and Star Wars was years afterward. In what condition might the THX 1138 original be, as well?

Why would a director make a "director's cut" (aside from marketing to fill his coffers) and arbitrarily trim the frame throughout his otherwise non-problematic movie? Could it be the negative was gone (for whatever reason) and the choice for source was the U.S. edge-enhanced-DNR'ed(?)-mess master or the U.K. cropped-but-non-processed master?

drngr said:

YouTube example using the HD72A to capture "The Dark Knight" Blu-ray from PS3 at 1080p24: http://www.youtube.com/watch?v=f1wezhH63Ow

and

Why can't you use a credit card with PayPal?

Unfortunately, if the buyer doesn't have a PayPal account, eBay won't allow the option to pay for an auction through it (because they want you to sign up). Sux to be me.  :)

Wow, a very nice capture of a 1080p source (even with YouTube compression)! But what is that occasional tearing-bar glitch at the top of a single frame now-and-then:

I saw the same thing on another YouTube demo of a video game capture. Is it something that happens always on the same frame(s) or is it random? Bad card, or bad signal, or bad computer, or bad something else? And, more important, any way to capture without getting it?

Thanks, glad to help.

Yep, it looks good! :)

BTW, I was looking over the sample shot from the U.S. & U.K. laserdiscs and discovered something interesting:

1991 US LD

1992 UK LD

1997 Bravo TV

2004 DVD R1

2010 Blu A/B/C

Notice? The top spacing of the doorways within the frames?
Lucas' Director's Cut of THX 1138 looks like it's from the U.K.-laserdisc source, not the U.S.-laserdisc source as one would expect.

And, of course, I had to revisit that old proof-of-concept on the U.S. laserdisc edition of THX 1138 -- now that I'm getting the hang of DeHalo_alpha settings. Back then, I max'ed it out to wipe the edge enhancement entirely (it can't -- the author described it as a "trick" function). Now, after a feel for what the numbers are doing and a minimum setting just enough to show improvement, all the unsightly edge-peaking is nicely diminished. It turns out that the only setting away from the defaults was to "turn off" (0.0) dark-edge processing, to operate only on the over-bright edges:

This is the only line of code (along with the already posted DeHalo_alpha script) to do the job:

video_DH = video.ConvertToYV12().DeHalo_alpha( darkstr=0.0 ).ConvertToRGB32()

msycamore said:

... I'm not so fond of the slight fuzziness it introduces going by that sample pic but it may be a worthy tradeoff I guess.

DeHalo_alpha seems to be the best they've got. I looked around for updates or other filters but none to be found. Even tried one that forced me to add sub-filter after sub-filter to eliminate successive "function not found" errors but it proved to be only fair at best.

So, I tried twiddling the parameters and discovered, for this application, the radius was too high. For the optimum setting, "5.0" is it -- lower and it doesn't do enough; higher and the "ringing" artifact starts to show.

                            rx=9.0, ry=9.0                                                                    rx=5.0, ry=5.0

As it's less drastic, the new correction isn't as overall soft, while doing a slightly better job reducing the leftover color fringing (no "added ringing" this time):

                     original                                        DeHalo @ 9.0                                             DeHalo @ 5.0

I'll update the previously posted Avisynth script parameters from "9.0" to "5.0" to keep the code correct.

@ Harmy

Even though done on this 720p sample, your example fix is a significant  improvement and probably good enough for the full 1080p. I think you've made someone happy. :)

@ msycamore

Spaced Ranger said:

Interesting that they look allot like edge-enhancement halo's.

A great storyteller always use foreshadowing. :)

Back on page 42, I demo'ed the DeHalo_alpha Avisynth filter on a noticeably EE'd laserdisc snapshot -- with mixed results.

Now, on the film capture, the de-focused edges in 2 of the 3 R/G/B separations have added different color fringing to the chromatic aberration problem. Applying DeHalo to the Red and Blue separations reduced the level of peaking on those bad edges:

                              BLUE separation                                                    BLUE separation DeHalo'ed

In this Blue separation, it flattens out the light and dark peaks. Of course, being in "alpha" development, it produces some artifacts of it's own. But those are less obtrusive and get lost when joined back to the other separations.

Using the same DeHalo settings on both Red and Blue (Green didn't have the edge damage) cleaned up what the chromatic aberration corrections couldn't (notice the shoulder and the collar across the 3 sections -- color fringing reduces as you move along):

            color corrected (cc)           cc & chromatic aberration correction (cac)             cc & cac & DeHalo

Note: color correction was applied later, in a paint program.

I did make one change in applying the chromatic aberration correction. Red seemed to be a very minor player and resizing it, even at a single pixel, didn't produce a noticeable improvement. So I adjusted only Blue and that seemed enough.

Here's the Avisynth script that produced this. DeHalo_alpha is an add-on script (not mine):

##====================
## THX 1138 16mm
## AviSynth 2.5.x script
##==========

## source
##----------
clip1 = ImageSource( "THX1138 16mm -0000.png" )
v1 = clip1.ConvertToRGB32()

## get RED / GREEN / BLUE channels
##----------
v1_R = v1.ShowRed()
v1_G = v1.ShowGreen()
v1_B = v1.ShowBlue()

## DeHalo & resize (chromatic aberration fix) each channel
##----------
## DeHalo_alpha()
## clip clp, float "rx", float "ry", float "darkstr", float "brightstr",
## float "lowsens", float "highsens", float "ss"
## - rx, ry [float, 1.0 ... 2.0 ... ~3.0] Default 2.0
# As usual, the radii for halo removal.
# this function is rather sensitive to the radius settings. Set it as low
# as possible! If radius is set too high, it will start missing small spots.
## - darkkstr, brightstr [float, 0.0 ... 1.0] Default 1.0, <0.0 and >1.0 allowed
# The strength factors for processing dark and bright halos. Default 1.0 both
# for symmetrical processing. On Comic/Anime, darkstr=0.4~0.8 sometimes might
# be better ... sometimes. In General, the function seems to preserve dark
# lines rather good.
## - lowsens, highsens [int, 0 ... 50 ... 100] Default 50
# Sensitivity settings, not that easy to describe them exactly ... in a sense,
# they define a window between how weak an achieved effect has to be to get
# fully accepted, and how strong an achieved effect has to be to get fully
# discarded.
## - ss [float, 1.0 ... 1.5 ...] Default 1.5
# Supersampling factor, to avoid creation of aliasing.
##----------

# DeHalo RED
v1_R_DH = v1_R.ConvertToYV12()
\.DeHalo_alpha( rx=5.0, ry=5.0, lowsens=99, highsens=99 )
\.ConvertToRGB32()
#\.Lanczos4Resize( 718, 480 ).AddBorders( 1, 0, 1, 0 ) #not needed

# do nothing to GREEN
v1_G_DH = v1_G

# DeHalo & resize BLUE
v1_B_DH = v1_B.ConvertToYV12()
\.DeHalo_alpha( rx=5.0, ry=5.0, lowsens=99, highsens=99 )
\.ConvertToRGB32()
\.Lanczos4Resize( 726, 484 ).Crop( 6/2, 4/2, 720, 480 )

# recombined "fixed" separations
v1_DH = MergeRGB( v1_R_DH, v1_G_DH, v1_B_DH )


## display the various results
##==========

#showclip = StackHorizontal( v1_R, v1_R_DH )
#showclip = StackHorizontal( v1_G, v1_G_DH )
#showclip = StackHorizontal( v1_B, v1_B_DH )
showclip = StackHorizontal( v1, v1_DH )
#showclip = v1_DH

showclip



##====================
## De-halo

# Here are the parameters:

# - rx, ry [float, 1.0 ... 2.0 ... ~3.0] Default 2.0
# As usual, the radii for halo removal.
# Note: this function is rather sensitive to the radius settings. Set it as low
# as possible! If radius is set too high, it will start missing small spots.

# - darkkstr, brightstr [float, 0.0 ... 1.0] Default 1.0, <0.0 and >1.0 allowed
# The strength factors for processing dark and bright halos. Default 1.0 both
# for symmetrical processing. On Comic/Anime, darkstr=0.4~0.8 sometimes might
# be better ... sometimes. In General, the function seems to preserve dark
# lines rather good.

# - lowsens, highsens [int, 0 ... 50 ... 100] Default 50
# Sensitivity settings, not that easy to describe them exactly ... in a sense,
# they define a window between how weak an achieved effect has to be to get
# fully accepted, and how strong an achieved effect has to be to get fully
# discarded.

# - ss [float, 1.0 ... 1.5 ...] Default 1.5
# Supersampling factor, to avoid creation of aliasing.

function DeHalo_alpha(clip clp, float "rx", float "ry", float "darkstr", float "brightstr", float "lowsens", float "highsens", float "ss")
{
rx        = default( rx,        2.0 )
ry        = default( ry,        2.0 )
darkstr   = default( darkstr,   1.0 )
brightstr = default( brightstr, 1.0 )
lowsens   = default( lowsens,    50 )
highsens  = default( highsens,   50 )
ss        = default( ss,        1.5 )

LOS = string(lowsens)
HIS = string(highsens/100.0)
DRK = string(darkstr)
BRT = string(brightstr)
ox  = clp.width()
oy  = clp.height()
uv  = 1
uv2 = (uv==3) ? 3 : 2

halos  = clp.bicubicresize(m4(ox/rx),m4(oy/ry)).bicubicresize(ox,oy,1,0)
are    = yv12lutxy(clp.expand(U=uv,V=uv),clp.inpand(U=uv,V=uv),"x y -","x y -","x y-",U=uv,V=uv)
ugly   = yv12lutxy(halos.expand(U=uv,V=uv),halos.inpand(U=uv,V=uv),"x y -","x y-","x y -",U=uv,V=uv)
so     = yv12lutxy( ugly, are, "y x - y 0.001 + / 255 * "+LOS+" - y 256 + 512 / "+HIS+" + *" )
lets   = maskedmerge(halos,clp,so,U=uv,V=uv)
remove = (ss==1.0) ? clp.repair(lets,1,0)
          \        : clp.lanczosresize(m4(ox*ss),m4(oy*ss))
          \            .logic(lets.expand(U=uv,V=uv).bicubicresize(m4(ox*ss),m4(oy*ss)),"min",U=uv2,V=uv2)
          \            .logic(lets.inpand(U=uv,V=uv).bicubicresize(m4(ox*ss),m4(oy*ss)),"max",U=uv2,V=uv2)
          \             .lanczosresize(ox,oy)
them   = yv12lutxy(clp,remove,"x y < x x y - "+DRK+" * - x x y - "+BRT+" * - ?",U=2,V=2)

return( them )
}

function m4(float x) {return(x<16?16:int(round(x/4.0)*4))}
##====================

After checking blu-ray.com for the reviews on both those movies ...

"Thin edge halos appear here and there, color fluctuations and minor bleeding seep into the presentation ..." - Phantom of the Opera (1943) Blu-ray

"... and red color fringe affects several shots. (Rope was shot using three-strip Technicolor, a process which hinged on the perfect alignment of three color separation negatives. If the red layer is a hair off, thin red lines occasionally appear that behave a bit like edge halos.)" - Rope (1948) Blu-ray

(even visible in their 720p "thumbnail": http://images.static-bluray.com/reviews/6908_4_large.jpg)

... then, yes, the chromatic aberration correction would allow you "correct" such alignment (moving the affect separations) and/or shrinkage (resizing the affected separations) "errors" after some by-eye experiments. Keep in mind the separations could be "misaligned" for any reason (shift, rotated, size, warp), not just the simple resizing for the THX 1138 film-capture here.

This particular "fix" is for chromatic aberration fringing -- see post on the previous page describing the particulars: http://originaltrilogy.com/forum/topic.cfm/THX-1138-preservations-Italian-Cut-available-see-1st-post/post/624565/#TopicPost624565. I wouldn't expect such a problem to be on a professional release.

However, if you are referring to effects of commercial publishers overusing their poorly implemented EE (Edge Enhancement), then, yes, there is a rudimentary Avisynth filter than can reduce that problem.

First, see post (also in this thread) for an explanation on the proper approach to "sharpen" an image, in Avisynth with the LimitedSharpen filter: http://originaltrilogy.com/forum/topic.cfm/THX-1138-preservations-Italian-Cut-available-see-1st-post/post/529702/#TopicPost529702.

For a possible reduction of EE fringing, see post (again, in this thread) for a demonstration of the DeHalo_alpha filter, also for Avisynth (I max'ed out the settings, for that demonstration, which created it's own problems): http://originaltrilogy.com/forum/topic.cfm/THX-1138-preservations-Italian-Cut-available-see-1st-post/post/552393/#TopicPost552393.

As always, filters are in constant development. Always research the Doom9 forums Avisynth sections for improved or new filtering.

@ SilverWook & msycamore

Thanks for the info. Too bad the VCD isn't a more useful source. I guess it's back to waiting for a possible(?) 16mm scope print.

@ msycamore

Because of the slightly de-focused RED and BLUE separations, the chromatic aberration correction will always have some color fringing (unless serious processing is applied to those color-seps to fix the fuzzed edges). Interesting that they look allot like edge-enhancement halo's.

While not perfect, the result is yet another improvement. This example is from the early paint program color correction test -- the later color correction in Avisynth / VirtualDub will, of course, look better:

                   CHROMATIC ABERRATION w/CC                                                 CORRECTION w/CC

Recently came across this reference, from an obscure forum (aren't we all?) :) , to an 2005 eBay auction:

Anyone have one of these "THX-1138" (only in the U.S. is the title "THX 1138") VCD's (Video CD)? I don't recall a mention of this in this thread. The original poster didn't have any more information but wondered aloud that it should be widescreen. And, of course, eBay no longer displays that auction (and presently has none like it).

Not many technical details there, but the operational description looks great:

"no sprockets, no advance claw, no capstan, no pinch roller, no belts, and no gears means virtually no maintenance. Nothing to lube, nothing to adjust. You don't even have to focus! ... Long life super bright LED produces zero hot spot, lasts thousands of hours and produces no heat on the gate or film. ... The Retro-8 features SafeScan zero image area contact at the gate and rubber guide rollers that handle the film only by the edges for maximum film safety. ... the Retro-8's Solid State Registration means a rock steady picture, generally accurate to within a pixel. The Retro-8 scans in full 24 bit color using industry standard square pixel orientation. HD output files are 16:9, 1080p with black bars on the left and right of the film frame."

The sample color-film frames are problematic as fringing there may be from the consumer-grade movie cameras. However, the B&W-film frames eliminate that possibility and do not show any fringing from the scanning process (as expected from a focus-less process):

A WorkPrinter trade-up might be worth the improved quality & convenience once a 16mm machine is available.

msycamore said:

I'm gonna do this bad boy justice. It's just that lack of time and motivation that gets in the way.

And here I've thinking up new ways to make more work for you! Better swallow hard before reading on ...  :)

When I first came across Puggo - Jar Jar's Yoda's Puggo GRANDE project using a WorkPrinter 16 for 16mm film capture ...

... I noticed color fringing on his samples and on samples from the manufacturer's (MovieStuff) website. Unfortunately, the capture he made for you suffers from the same color fringing:

Notice the bluish color (typical for "chromatic aberration") showing at the high contrast, outer edges (the boy's shoulder and SEN's neckline & the back of his head). The suspect of this crime is the huge lens on the WorkPrinter that focuses the film frame into the capture camera. This "simple" (single-element) lens focuses the colors of the light spectrum at fractionally different distances, causing the aberration:

https://en.wikipedia.org/wiki/File:Chromatic_abberation_lens_diagram.svg

A multi-element lens would correct this but it would also be much more expensive, especially with a lens that big.

The problem is the R/G/B components of the picture are no longer the same size. Like Goldilocks And The Three Bears, the RED is too big (and slightly out of focus), the BLUE is too small (and slightly out of focus), but the GREEN is just right (and in focus). In this R/G/B separation ...

... notice that the RED edging seems to be the reverse of the BLUE edging (the GREEN, of course, has no edging). This indicates the GREEN is in focus and the proper size. The other 2 need correction.

The solution is simple -- resize the BLUE and RED separations to create a chromatic aberration correction. I did this by

• SEPARATING the captured frame (720x480) into R/G/B components
• RESIZING up the BLUE to 726x484 and CROPPING the larger result back to 720x480
• RESIZING down the RED to 718x478 and BORDERING the smaller result back to 720x480
• COMBINING the new R/G/B components into a corrected frame

                       CHROMATIC ABERRATION                                                       CORRECTION

For this "proof of concept", I worked on the full-sized frame. However, it should be applied to a double-sized frame to allow for "single pixel" resizing while keeping the picture elements centered. Otherwise, you may end up with a single-pixel-shift error (as I did here on the RED separation -- producing a RED fringe at the farthest right edge of the picture).

drngr said:

Only recently, the HDMI boards have started showing up on eBay instead of just the import sites.

Are there any non-eBay sites (like the DX site -- easily available to the U.S. with normal credit cards) that carry these items? The HDMI 3D Splitter 1x4 looks useful and capping up to 1080-24p (including all the lower resolutions) should cover any future situation. Raw capturing is useful (especially for later editing), but unobtrusively compressed recordings, for later viewing with a minimum of fuss, is fine (in this ease-of-use scenario, HDMI for recording both video and audio would be best).

Only ... I can't determine which products produce "clean" signals for recording just by reading the minimal descriptions. Any pointers on what to look for?