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Best sampling depth for digitizing cassette recordings

 
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chetstone



Joined: 17 May 2009
Posts: 8
Location: Crestone, CO, USA

PostPosted: Wed Jan 05, 2011 6:56 pm    Post subject: Best sampling depth for digitizing cassette recordings Reply with quote

I recently started digitizing my cassette recordings at 44.1kHz/24 bits because it must be "better", right? But I cannot think of why it would be better than 16 bits.

The cassettes are of quite high quality, recorded on metal or high-quality chrome tape (I'm a bit surprised by the good shape these tapes are in after 25 years). Some are recorded with Dolby B, others without noise reduction.

Still, at best the tapes have a 72db dynamic range, so 24 bit digitization will just be encoding the tape hiss with more accuracy.

Can someone suggest a good rationale for going with the deeper sampling (or higher bit rate for that matter)?

Thanks.
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Martin Hairer
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Joined: 08 Nov 2006
Posts: 1615

PostPosted: Wed Jan 05, 2011 9:48 pm    Post subject: Best sampling depth for digitizing cassette recordings Reply with quote

Quote:
Still, at best the tapes have a 72db dynamic range, so 24 bit digitization will just be encoding the tape hiss with more accuracy.

That would be my guess, yes, but maybe someone with more experience
will chime in... Regards,

Martin

HairerSoft
http://www.hairersoft.com/


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rfwilmut



Joined: 17 Nov 2006
Posts: 255

PostPosted: Wed Jan 05, 2011 11:20 pm    Post subject: Re: Best sampling depth for digitizing cassette recordings Reply with quote

The higher the sampling rate and bit depth the smaller the errors in quantization - remember that every sample has to be approximated to the nearest step defined by the binary numbers. These errors basically take the form of noise - a sort of fizzing noise rather than clean hiss - but even with CD quality it's 90dB below absolute peak (of course you should be working right up to peak). Increasing the sampling rate and bit depth will reduce the noise: it's additive to the existing tape hiss but the increase is absolutely minimal even at 90dB. Remembering that the definition of peak level even in open-reel tape is 3% distortion, and given the inherent hiss level even with Dolby B, I have to say that I doubt you would hear any improvement over CD quality (44.1kHz, 16 bit), much less over 24 bit.
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Lou Kash



Joined: 16 Jul 2008
Posts: 87

PostPosted: Wed Jan 05, 2011 11:35 pm    Post subject: Reply with quote

The point of recording in 24bit is mainly having lots of "headroom" for further editing. You can record at relatively low gain, then you can process your recording as you like - denoise, compress, limit, equalize etc. In the end you can then normalize the recording to, say, -0.5 dBFS and convert to 16bit for archiving.
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chetstone



Joined: 17 May 2009
Posts: 8
Location: Crestone, CO, USA

PostPosted: Thu Jan 06, 2011 1:45 am    Post subject: Reply with quote

Lou Kash wrote:
The point of recording in 24bit is mainly having lots of "headroom" for further editing. You can record at relatively low gain, then you can process your recording as you like - denoise, compress, limit, equalize etc. In the end you can then normalize the recording to, say, -0.5 dBFS and convert to 16bit for archiving.


Yes, that makes a lot of sense. In my case though I want to archive the
raw digitized file before editing. I then do some rough editing, break it into tracks and compress to AAC and put it in iTunes for casual listening. If I ever want to do some more serious editing I want to have the raw file available from my archives. If I have 16-bit archives (which the other posters have agreed is adequate), is there a way to convert it to 24 bits to get more headroom, then proceed to do my serious edits as you describe?

Also, what is dBFS? Would that correspond to normalizing to -0.5db "maximal sample value" in Amadeus?

Anyway I guess the way I've been recording in 24-bit doesn't give me any benefit because I've been recording at the same gain as I record in 16-bit -- about -6dB peak. I'd need to turn down the output level on my cassette deck to do as you describe.
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