Digitising Cassettes

[ef37a]

@ef37a FWIW I've found the TDK SX cassette shells wobbly even when I used them back in the early nineties at double speed in a four track. Sony UX-S were better, with the Maxell XL series being better again, and the XL-IIS seem to be the smoothest (although probably identical to XL-II).

Practitioners have been adjusting pre decoder gain for a long time.

This is (another) good example of your selective reading. I did mention the technique in my first post... Perhaps I wasn't clear in the post you're quoting, so I'll clarify. The clever bit I was referring to in James's post is doing the transfer without decoding, and leaving the level adjustment, with decoding, to the Uhe plugin afterwards.

FYI these are TDK SA 90 and on the 'spine' of the shells is printed AHKJ217-36.

I never had any problem with TDK mechs back in the day nor Maxell but my machine was biased for SA and AD so that was my main buy. If I had a machine in with a tangled tape the cassette was invariably a cheap one.

Dave.

[Tim Gillett]

Practitioners have been adjusting pre decoder gain for a long time.

This is (another) good example of your selective reading.

We can all be selective at times. If you can show me where I've been selective I'd be grateful.

I did mention the technique in my first post...

Yes you seemed to refer to play trim. I've just read that post in detail. Glad you are aware of it and its importance in achieving Dolby tracking.

Perhaps I wasn't clear in the post you're quoting, so I'll clarify. The clever bit I was referring to in James's post is doing the transfer without decoding, and leaving the level adjustment, with decoding, to the Uhe plugin afterwards.

Sure, but again that's hardly new. I started doing this many years ago with an outboard hardware analog decoder (gain staging needs to be done well) and I'm sure others did it well before then.

The only difference here is using a software decoder rather than a hardware.
Software is easier but it still needs a "home" reference IMO. Whenever I used this technique I always recorded in the file a reference tone for Dolby level, 200 nWbm from the playback machine which itself was well calibrated. Even if the actual recording doesn't strictly line up with Dolby level tone, the transferred 400Hz tone is a baseline of sorts from which to branch out, gain up or gain down.

You're already familiar with the "play trim" principle. The input gain adjustment is important too as Hugh mentioned. The two together are IMO the standard tools for this. Both are often needed although often it's the "play trim" type of tool which is more decisive because as we know many cassettes are vulnerable to loss of highs. Knowing that, (I'm speaking generally here, not to anybody in particular) why persist in just adjusting overall input gain? It makes no sense. If the tracking problem seems mainly due to a loss of highs, try and correct the highs with EQ. Target the actual error. Don't simply adjust overall gain. It will only introduce another error. (Happy to explain that if needed). Glad you're aware of both adjustment methods.

Tim

[Tomás Mulcahy]

[TheBev]

12" singles also often overload the inputs when fed from a Rotel receiver. I ended up making some attenuating cables for mine - I used 22k ohm resistors in series with the input (which already has a 22k resistor from signal to ground inside the unit) but if I was doing it again I'd go for a slightly higher value.

Hi James, sorry an old thread resurrection / question if I may.
I was wondering what value of resistor you would go for now, if you did this again. I ask because getting some cables made up for just this scenario could be very useful for me and I was thinking of approaching Orchard Electronics.

And thanks btw, I never even knew this could be a 'thing'.

[James Perrett]

I seem to remember that 22k resistors were just about enough but they didn't leave any safety margin. So I'd probably go up to 33k resistors if I was doing it again.

However, the proper way to do this would be to use a potential divider and, since this thread first appeared, I discovered a cheap inline variable attenuator that looks like it might well do the job as mentioned in this thread

https://www.soundonsound.com/forum/view ... 15&t=72480

The direct link is

https://www.ebay.co.uk/itm/Universal-Ca ... 0677.m4598

but I would add the priviso that I've not used one personally.

[TheBev]

Thanks for that James, that looks reassuringly cheap.
I'll head over to that thread maybe and ask if Dave (ef37a) ever took one apart and what the verdict was.

[ef37a]

Thanks for that James, that looks reassuringly cheap.
I'll head over to that thread maybe and ask if Dave (ef37a) ever took one apart and what the verdict was.

I can preempt your question and tell you, no. However, a potentiometer in a box and two RCA (look to be both female) cables? "What could possibly go wrong?"

Really, not a lot. They would have to be incredibly incompetent to bugger that up!

If you have a lot of copying to do it might be an idea to make a 'calibration' tape? You can generate a tone in any DAW (def' Audacity) I suggest the standard 333Hz for cassette at Dolby level (just because it is there!) Then set that to some chosen level in the recording process, say -12dBfs. You are very unlikely to have cassettes with level that far above Dolby.

That might seem a low level in the DAW but is not really and you can boost it digitally at the finish, even at 16 bits, noise will be way,way below even Dolby B tapes.

Dave.

[TheBev]

Thanks Dave, that's me sold then.

Most of my tapes were already copied some years ago but I'd like to redo a few as I'm one of those eejuts who strayed into (well into) the red on occasion.
Out of interest though is the box a better approach than say the Canford solution?

[James Perrett]

Out of interest though is the box a better approach than say the Canford solution?

Electrically they'll do pretty much the same thing. The Canford attenuators look very robustly built and they look like they are closely matched so that you know the attenuation with two of them in use will be within 0.2dB at worst. The variable attenuator box is more versatile but channel matching may not be as good and it will probably break if you tread on it.

[Tim Gillett]

12" singles also often overload the inputs when fed from a Rotel receiver. I ended up making some attenuating cables for mine - I used 22k ohm resistors in series with the input (which already has a 22k resistor from signal to ground inside the unit) but if I was doing it again I'd go for a slightly higher value.

Hi James, sorry an old thread resurrection / question if I may.
I was wondering what value of resistor you would go for now, if you did this again. I ask because getting some cables made up for just this scenario could be very useful for me and I was thinking of approaching Orchard Electronics.

And thanks btw, I never even knew this could be a 'thing'.

I would only attenuate if on the loudest cassette using your cassette deck, the converter clips. Otherwise there's no point.

[TheBev]

The variable attenuator box is more versatile but channel matching may not be as good and it will probably break if you tread on it.

So long as it doesn't break when I look at it I suppose, thanks James, more food for thought and all good info

I would only attenuate if on the loudest cassette using your cassette deck, the converter clips. Otherwise there's no point.

Yes Tim, that was kind of the whole point.

[ef37a]

12" singles also often overload the inputs when fed from a Rotel receiver. I ended up making some attenuating cables for mine - I used 22k ohm resistors in series with the input (which already has a 22k resistor from signal to ground inside the unit) but if I was doing it again I'd go for a slightly higher value.

Hi James, sorry an old thread resurrection / question if I may.
I was wondering what value of resistor you would go for now, if you did this again. I ask because getting some cables made up for just this scenario could be very useful for me and I was thinking of approaching Orchard Electronics.

And thanks btw, I never even knew this could be a 'thing'.

I would only attenuate if on the loudest cassette using your cassette deck, the converter clips. Otherwise there's no point.

Unless I have missed it and things have moved on? The UCA202 is the interface and these can have their inputs overloaded but this is unlikely IMEx from a cassette deck. I would never hit one harder than -6dBfs.

CLUCK it! I shall HAVE to do a headroom test now to sort the matter out in MY brain!

Dave.

[Tim Gillett]

I would only attenuate if on the loudest cassette using your cassette deck, the converter clips. Otherwise there's no point.

Yes Tim, that was kind of the whole point.

Ah so when you spoke of occasionally going into the red you meant digitally, not when recording the cassettes?

[Mike Stranks]

There are plenty of this type of attenuator around which appear a bit more robust...

I have used: https://fostexinternational.com/docs/products/PC-1eBW.shtml

and

https://www.monacor.com/products/pa-technology/volume-controls-and-accessories/volume-controls/ila-100rca/

There's also the Behringer 'Monitor 1'...

... but all varying degrees of more expensive than the one already discussed here!

[TheBev]

CLUCK it! I shall HAVE to do a headroom test now to sort the matter out in MY brain!

Dave.

Dave - we're talking about tapes that were absolutely saturated going into the red but maybe they weren't clipping and I've misremembered, t'was as I say some years ago now.
But going forward it was more for vinyl transfer tbh than the half a dozen or so 'songs' that I abused, they were simply an afterthought really, just to see if there could be any improvement.

I find with my set up even some LP's clip, or are v close to it, let alone 12" singles which James mentioned and is what initially piqued my interest.

And Tim, see above, but in short it was both.

[ef37a]

CLUCK it! I shall HAVE to do a headroom test now to sort the matter out in MY brain!

Dave.

Dave - we're talking about tapes that were absolutely saturated going into the red but maybe they weren't clipping and I've misremembered, t'was as I say some years ago now.
But going forward it was more for vinyl transfer tbh than the half a dozen or so 'songs' that I abused, they were simply an afterthought really, just to see if there could be any improvement.

I find with my set up even some LP's clip, or are v close to it, let alone 12" singles which James mentioned and is what initially piqued my interest.

And Tim, see above, but in short it was both.

No, still going to do the test to keep me happy!

Now, copying vinyl is different I think level wise.
Whereas tape can really not go more than few dBs about Dolby level, you can get massive spikes off discs. I therefore record at 24 bits and way down at -30dBfs so that spikes do not clip the converter.

I did this for a stack of my daughter's 45s then de-noised and de-clicked them using the free demo time of Sony (then) Sound Forge. Then boosted to around -6dBfs top whack.

Dave.

[jimjazzdad]

Does no one use a good, transparent, analogue clipper/limiter on the way into their AD interface? For years I have had an Aphex 720 strapped on the end of my analogue chain - its carefully calibrated and completely inaudible unless you deliberately 'slam' it. I do a lot of radio segments for upload and it is indispensable there but it also comes in very handy preventing occasional digital 'overs' when dubbing all sorts of analogue media...

[TheBev]

Now, copying vinyl is different I think level wise.
Whereas tape can really not go more than few dBs about Dolby level, you can get massive spikes off discs. I therefore record at 24 bits and way down at -30dBfs so that spikes do not clip the converter.

Dave.

I would be interested in the results Dave if you have the time

I *was* leaning toward the Canford jobbies, they seem pleasingly discrete for my already cluttered desktop but am now thinking they may not offer enough attenuation, I was aiming for-18 to -20dbfs for the vinyl and don't think the Canfords are man enough for the job.
And now Mike has thrown some more options into the pot to confuddle me further. Thanks Mike btw.

[Mike Stranks]

And now Mike has thrown some more options into the pot to confuddle me further. Thanks Mike btw.

My pleasure!

... and there's also Fentronix... I have a couple of their useful little gizmos - including a well-made attenuator. Happy hunting!

[James Perrett]

... but all varying degrees of more expensive than the one already discussed here!

Don't forget that we're talking about £20 audio interfaces here. You could buy a proper audio interface with input level controls for the price of that Monacor level controller.

In fact this part of the thread seems to be a little out of proportion generally. If you are going to spend £30 or more on attenuators then you might as well just buy something like the Behringer UMC202HD which gives you level controls, 24 bit convertors and high sample rates (which can be useful for de-clicking vinyl).

If you have a spare phono cable lying around and a few resistors then making your own attenuator cable makes sense but buying attenuators at full price for a £20 audio interface doesn't make sense to me.

[Hugh Robjohns]

Quite so, James.

Another suggestion I'd make is for the ART Cleanbox Pro which does a very tidy job of converting an unbalanced consumer output from a cassette or RIAA preamp to a balanced professional line level signal, with adjustable gain controls.

[ef37a]

Not sure what the maximum input of the UMCs is but will check later. My UMC240HD delivered only about a volt in line output so I doubt the line in headroom was little more?

AI front controls are GAIN controls, they don't attenuate the incoming signal.

Dave.

[TheBev]

Ah I see I should clarify a bit, I actually have an RME UCX if that makes a difference.
There are 3 different input sensitivities for the analog inputs but even at the lowest setting I still get clipping whilst recording some vinyl, and get nowhere near the -20dBfs range for all.

[James Perrett]

That puts a completely different slant on things.

It might help if you gave us details of the whole signal chain as I would have thought that it would be very difficult to get anywhere near the UCX's max input of +19dBu with a domestic hifi system.

[Hugh Robjohns]

I actually have an RME UCX .... There are 3 different input sensitivities for the analog inputs but even at the lowest setting I still get clipping whilst recording some vinyl...

As James says, we need to know the signal chain because there aren't many consumer RIAA preamps that can push out peaks over +19dBu (which is the clipping level at the UCX's lowest sensitivity setting). A professional one could, though, on click transients at least.

This chart compares the three RME analogue sensitivity options with the SMPTE and EBU recommended alignments. As you can see, the +19 option on the RME actually matches the EBU broadcast standard (with an extra 1dB safety margin!), but I've shown it here with the SMPTE alignment level of +4dBu instead of the EBU's 0dBu since that's what most home studios operate with!

(The yellow region on each bargraph indicates the 9dB nominal programme range between the Alignment Level (green/yellow border) and the Maximum Permitted Level (yellow/red border), with the red area above showing the different systems' headroom margins.