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Cassette Audio Digitization - optimizing quality

Hi.

I have some questions about digitizing audio cassette tapes. I have done it many times, but this is more about optimizing the quality.

Here’s what I am thinking:

- Cassette deck. Obviously the better the cassette deck, the better the captured quality. I have one that I am happy with.
- Computer to record the audio signal from the cassette deck. I have a Mac.
- adapter or converter? this is where I am stuck.

  • An adapter would allow the analog cables of the cassette deck to be plugged into the computer. The computer would then do the the analog-to-digital conversion (ADC).
  • Or, a converter-box could be used instead for the analog-to-digital conversation (basically a standalone computer). The box would receive the cables from the cassette deck, digitize the signal, and send it to the computer via USB. In this latter case, the converter is also acting as an adapter as well.
Basically, some questions that come to mind:
- if I choose to get an adapter, then the computer will do the ADC, right? And if so, the quality of the ADC depends on the sound-card, right? So typically, a sound card in a 2020 iMac computer will be better than a sound card from a 2002 Compaq Windows ME computer, right? And if so, will the difference be negligible or major?
- if I choose to get a converter, then in a sense, am I simply getting another computer, one that is dedicated with only the task of performing the ADC before sending that digital-signal to the Mac for recording? If so, then what would make this method preferable to going the adapter route? Is it that these external ADC boxes just have a really good sound card? (Assuming that I buy a high end unit; there are plenty of cheap ones around, which makes me wonder if I’d just be working backwards at that point rather than using an adapter.)

Let me know your thoughts please.

Thanks.

Comments

bouldersound Sun, 05/17/2020 - 16:04

The cassette player is a likely weakest link in the chain. If it's a different player than the one the cassette was recorded on then there's likely at least a small difference in head alignment between the original record deck and the playback deck. That will cause a small but unrecoverable loss of quality. When I want to absolutely optimize the transfer I'll adjust the playback deck's head to the tape, generally by ear but often with a phase meter to assist. I have a set of procedures for this, including boosting the crap out of the HF on my playback system etc.

The built in audio is often fairly good. It might be adequate. But since you said you want to optimize the quality, I'd go with a decent audio interface with 24 bit converters. The noise floor of cassette is such that 16 bit converters would be good enough, but having the space to digitize a signal without having to worry at all about clipping makes the whole process easier.

jgiannis Sun, 05/17/2020 - 16:40

Thanks for the replies guys.

Just for the sake of argument, let’s say you had 4 setups. (Assume that the deck and it’s output are identical in all 4. Assume I only want 24-bit, 48k audio and that all 4 are capable.)

Cassette deck (trs jack) > $35 external ADC box (receives trs, outputs USB) > 2020 Mac for recording

Cassette deck (trs jack) > $3,500.00 external ADC box (receives trs, outputs USB) > 2020 Mac for recording

Cassette deck (trs jack) > 2002 Compaq for recording (receives the trs input directly into sound card)

Cassette deck (trs jack) > 2020 Mac for recording (receives the trs input directly into sound card)

Again, assuming that the cassette deck outputs the exact same signal in each scenario and that the bit/sample depth is the same in all 4, which method do you think will be the best? Or will they be identical?

kmetal Sun, 05/17/2020 - 17:17

The Macs probably a bit better than the compaq, and roughly the same as the 35$ soundcard.

The 3,500 adc will be best. It just wouldn't be 100x better than the 35$ adc.

It just comes down to if you want the absolute state of the art, entry level, or mid level. Mid level converters are quite good.

bouldersound Sun, 05/17/2020 - 17:18

That's a weird array of options. I would not bother spending $3.5k. I'd have to know what $35 box you're talking about. The computer itself probably doesn't matter.

[Edit] For the line input, I'd definitely go with the newer computer as long as it could accommodate stereo consumer line level signals. But I'd still rather have a decent external converter.

jgiannis Mon, 05/18/2020 - 22:53

This topic isn’t so much about specific devices as it is about the general notion of the variability of ADCs. The market has a wide range in scale so it’s something that I wonder about.

I asked about the 2002 Compaq because I actually used that when it was new. Now I wonder if that’s a reason to suspect inferior quality relative to my modern Mac. Or perhaps this technology hasn’t had much way of improvement.

The idea of a $35 ADC vs a $3,500 one isn’t specific. One of them implies bottom-of-the-line technology while the other implies top-of-the-line (and these are actual price ranges). So it’s more of an idea of what the heck the difference between these could do for audio. We hear quite a bit about high tech audio gear, but not so much about ADCs and DACs. Obviously “better” models will have more features (ie higher sample and bit rates) and have higher dependability and can probably be rack-mounted, etc. But despite these bells-and-whistles, is there really a difference in audio-quality when both the high- and low-end models are capturing at 16/44.1?

kmetal Tue, 05/19/2020 - 15:22

jgiannis, post: 464327, member: 45032 wrote: Obviously “better” models will have more features (ie higher sample and bit rates) and have higher dependability and can probably be rack-mounted, etc. But despite these bells-and-whistles, is there really a difference in audio-quality when both the high- and low-end models are capturing at 16/44.1?

Yes there is a difference. In addition to Boswell's post, there's lower distortion, better clocking, more depth, better stereo imaging, smoother frequency response, possibly dsp effects, better power supply.

Sample and bit rate doesn't necessarily reflect audio quality. Its more like how many miles per hour a car goes, two cars can go the same speed, one with a much smoother, quiter ride.

pcrecord Wed, 05/20/2020 - 05:23

Casette tape players have different qualities, but you are still limited by the media. Inherent noises will be your culprit for any low audio quality.
Most people that do transfers like that will use restoration tools, like iZotope RX.

At least you aren't trying to get wispering behind a wall at a party, recorded on an iphone.. ;)

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