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Dynamic range of compact cassette - mastering audiobooks

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Dynamic range of compact cassette - mastering audiobooks

Postby Crystaljuggler » Sun Jul 24, 2011 8:02 am

I'm working on a review of recording and production processes for a company that produces audiobooks on CD, MP3 and compact cassette, and I'd appreciate it if someone could shed a little light on the subject of mastering for different formats.

At present, on all our output, we apply the standard Pro Tools limiter such that peaks don't hit greater than -5, and the quieter parts of the audio are above -10, going by the meters at the top of the plugin. This is ostensibly to deal with the "limited dynamic range of cassettes", but I can't for the life of me find anything that will tell me what that dynamic range is, how hot a signal tapes can actually handle, or whether these settings are appropriate. Can anyone tell me what sort of peak a cassette tape can actually handle or what we should be shooting for?

Since we master once, and then use that same audio for our CDs and MP3s, I'm concerned that we're doing ourselves a disservice by needlessly over-limiting. Any advice is appreciated.
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Re: Dynamic range of compact cassette - mastering audiobooks

Postby tacitus » Sun Jul 24, 2011 12:08 pm

I can't remember the figures, but the theoretic dynamic range of cassettes isn't much, and cheap cassette players don't even manage that. Even allowing for the fact that there must be millions of cassette players still kicking around, are there really enough people without CD or mp3 facilities to make it worth while any more? I certainly wouldn't master for CD/mp3 purely on the basis of what works on tape. On the other hand, if you decide that a limited dynamic range is just the ticket for the stuff you're doing, it might be an acceptable path. I expect the wikipedia article on cassette tape will give you the data you need.
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Re: Dynamic range of compact cassette - mastering audiobooks

Postby Exalted Wombat » Sun Jul 24, 2011 12:22 pm

Don't worry about making allowances for tape while preparing your digital master. It shouldn't peak over full-scale, because on digital that sounds bad! Apart from that, there's no reason not to use all the bits.

The numbers don't matter when transferring to cassette. Send the recorder a clean analogue signal. Set the recording level appropriately (and it's difficult to say more than that - tape CAN be driven quite hard, and often should be! After some experimentation you'll conclude that maybe an 0dB test tone from the digital system should align to +3dB on the cassette meters. Once established, stick to that. Your clients will appreciate consistent levels!)

Actually, the "limited dynamic range" of cassette is about a high noise floor rather than a lack of headroom. You can "go over" onto tape with impunity (within reason!) It's digital media that react violently to overload.

Above all, sample the product, on all media types, frequently. Check it sounds good, and do something about it if it doesn't! (How often are the cassete tape heads cleaned and aligned?)
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Re: Dynamic range of compact cassette - mastering audiobooks

Postby Tomás Mulcahy » Sun Jul 24, 2011 1:18 pm

Cassette- distorts easily, and is very noisy. Wombat is right about regular checking. This is the irritating, session interrupting part of using any analogue tape medium.

You can measure it- play a blank tape into Pro Tools and read off the noise floor. The reason you can't get a figure is that varies wildly depending on what tape you use, NR in or out, and quality and setup of the machine. I would think around -65dBFS for the noise floor would be the best achievable.
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Re: Dynamic range of compact cassette - mastering audiobooks

Postby . . . Delete This User . . . » Sun Jul 24, 2011 1:28 pm

offhand, i think the best dynamic range figure i recall is in the region of 72-75dB for a nakamichi deck.... and that's not a "fair target" as they stepped away from the "standard" to achieve that, and as such the tapes recorded on that were not playable on other machines....


most machine and tapes adhering to the standard format would struggle to get past 60-65dB
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Re: Dynamic range of compact cassette - mastering audiobooks

Postby Exalted Wombat » Sun Jul 24, 2011 4:00 pm

Off duty BBQ lighter AKA Idris wrote:offhand, i think the best dynamic range figure i recall is in the region of 72-75dB for a nakamichi deck.... and that's not a "fair target" as they stepped away from the "standard" to achieve that, and as such the tapes recorded on that were not playable on other machines....


most machine and tapes adhering to the standard format would struggle to get past 60-65dB

As bad as vinyl! i.e. more than good enough for perfectly enjoyable music and perfectly intelligible speech.

Did the Nak machines really record incompatible tapes? What for? There were higher-quality systems available - what was the point in recording an incompatible cassette?
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Re: Dynamic range of compact cassette - mastering audiobooks

Postby . . . Delete This User . . . » Sun Jul 24, 2011 4:57 pm

what practical higher quality systems were available to the consumer from the mid70's ?? to early 80's ??


THAT was the hey day of cassette

reel to reel was not a practicable consumer format. it never was.... too much space, and not enough stockists of quality tape, too expensive, and a heap of other issues..... very few people had a reel to reel recorder capable of any better performance than the top end cassette machines, and they cost as much, usually more.... but were much less convenient.


decent chrome tape using Dolby , could give you fairly decent playback in the car, and the home, without wearing out the vinyl...

towards the end, a decent deck, using decent tape, Dolby C and HXpro, did a pretty damn good job all things considered, for a much lower cost than DAT,.



it was a shame DCC flopped.... the timing was just too late..... and it wasn't marketed well, and the stupid hardware licensing policy killed it....


the 2nd/3rd generation DCC machines actually sounded pretty damn good....
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Re: Dynamic range of compact cassette - mastering audiobooks

Postby Smellthevalve » Mon Jul 25, 2011 12:39 am

Don't forget Dolby S, better than C although not found on many decks.
re: nakamichi, I've found it can reanimate an old cassette recording
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Re: Dynamic range of compact cassette - mastering audiobooks

Postby Crystaljuggler » Mon Jul 25, 2011 7:12 am

Thanks for all the input - quite a lot to think about! Part of the problem is that we don't have any control over how the cassettes are produced, as they're done off site, so we have to come up with a reasonably bomb-proof solution. From what I can gather, what we're doing is not unreasonable, except in the sense that our CDs don't sound as good as perhaps they could, but we don't have the luxury of being able to spend a lot of time remastering for different formats so it'll have to do for now.

Thanks all for your help - until we stop producing tapes, it's good to know there are people out there who know about such things!
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Re: Dynamic range of compact cassette - mastering audiobooks

Postby Tomás Mulcahy » Mon Jul 25, 2011 8:53 am

Crystaljuggler wrote:they're done off site

Talk to the engineer. It's likely they're already putting eq and a limiter in the path. You should have control- you're a paying client...
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Re: Dynamic range of compact cassette - mastering audiobooks

Postby Andi » Mon Jul 25, 2011 9:52 am

How much time would it actually take to re pre-master, if actually required, for cassette vs producing what you feel is substandard output (with your reputation attached to it) for the most commom media currently used on the planet? All the noise reduction and editing work will still be good and won't have to be re-done. I can see effort being required to re-master from cassette to CD or MP3 in some cases, but the other way? You're surely not using much dynamic range anyway and spoken word doesn't tend to cover too extreme a frequency range so I'd have thought that the transfer would be pretty simple? Unless, of course, King Diamond has started reading Audio Books?

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Re: Dynamic range of compact cassette - mastering audiobooks

Postby Folderol » Tue Jul 26, 2011 8:37 pm

In real terms, assuming the users have a conventional player I wouldn't assume more than 50dB S/N.

Dolby is moot, because, again the user probably won't have it, in which case it will simply appear to increase the noise/distortion as the treble content will be unnaturally lifted and compressed.

As suggested go over the top into tape saturation. If it's pure speech with no music content you might get away with +5dB, but if there's music with any bass content it would tend to produce the 'gurgling' inter-modulation distortion.

Experiment with different tape formulations, but I don't recommend FeCr Tape. OK you'll get a bit more output and better HF performance but at the cost of wearing tramlines in the users player, which almost certainly will not have hardened, glass or ferrite heads,
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