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Old 10th Sep 2019, 11:54 am   #21
PsychMan
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Default Re: Digital 'cassette' recorder

Fascinating build here, really like the idea.

What "sample rate" is used to sample the audio, And also bit depth of the ADC? Assuming those are valid terms to use here

In short, what audio quality can be expected?
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Old 10th Sep 2019, 8:31 pm   #22
Karen O
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Default Re: Digital 'cassette' recorder

PsychMan,
Good question!

I was aiming for a similar frequency response and SNR to an ordinary cassette recorder, back in the day. I chose a sample rate of 31.25kHz to achieve a 10kHz bandwidth (with a little room for filter roll-off), and an SNR of 50dB or so. I used 10 bit samples, mostly because the PIC's ADC is ten bits.

Although 8 bits would give theoretically 48dB SNR, there is an undesirable effect whereby the noise seems to 'come up' as a sound decays. It's kinda like a 'fffffff' sound during the decay of say, a piano note. 10 bits seems to stop that.

Oh, and it's mono of course!
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Last edited by Karen O; 10th Sep 2019 at 8:37 pm. Reason: Mention that it's monophonic
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Old 10th Sep 2019, 9:47 pm   #23
Karen O
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Default Re: Digital 'cassette' recorder

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Karen's cassette player is gorgeous
Praise indeed, David, Thank you.
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Does Dr Who use Old New Stock parts for his/her Tardis?
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Old 11th Sep 2019, 11:17 am   #24
Andrew2
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Default Re: Digital 'cassette' recorder

What a fascinating project, Karen. And the look is wonderful, rather like something one would see in a 70's school, knobs an' all.
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Old 11th Sep 2019, 1:25 pm   #25
PsychMan
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Default Re: Digital 'cassette' recorder

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Originally Posted by Karen O View Post
PsychMan,
Good question!

I was aiming for a similar frequency response and SNR to an ordinary cassette recorder, back in the day. I chose a sample rate of 31.25kHz to achieve a 10kHz bandwidth (with a little room for filter roll-off), and an SNR of 50dB or so. I used 10 bit samples, mostly because the PIC's ADC is ten bits.

Although 8 bits would give theoretically 48dB SNR, there is an undesirable effect whereby the noise seems to 'come up' as a sound decays. It's kinda like a 'fffffff' sound during the decay of say, a piano note. 10 bits seems to stop that.

Oh, and it's mono of course!
Thanks Karen, I bet it sounds pretty good, and again love the idea and the build quality of what you've made.

Its inspiring stuff. I might have to have a go at something similar myself with Arduino boards. I have used PICs a long time ago, and might revisit, but I find Arduinos a lot simpler to throw things together if you have less patience

I hadnt considered using them for audio before, but with ethernet modules as well, Id be interested to experiment with sampling audio and sending it over ethernet to a device for playback
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Old 12th Sep 2019, 1:33 am   #26
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Default Re: Digital 'cassette' recorder

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The simplest way is often the best. People forget that our ears are analogue devices which can only receive sound waves. Any digital source, even with DRM protection, can be recorded by tapping into the chain at the appropriate point. A microphone in front of the speaker if necessary.
The same goes for photos or video, you can just point a camera at the screen if you only need a low-quality image for reference.
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Old 12th Sep 2019, 11:41 am   #27
Karen O
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Default Re: Digital 'cassette' recorder

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love the idea and the build quality of what you've made
I confess, I didn't construct the wooden case for my player/recorder. It is an 'egg house' purchased from a homewares chain. My woodwork is good for shipping crates but not much more besides
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Old 12th Sep 2019, 1:39 pm   #28
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It is an 'egg house' purchased from a homewares chain.
Innovative as ever. Looks fantastic.

Steve
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