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Is it be possible to use a hdd head to record and play analogue signal/sound?

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Is it be possible to use a hdd head to record and play analogue signal/sound?

Postby Nikulnickel » Thu Aug 01, 2019 10:48 pm

I have been experimenting using the read/write heads of tape recorders for a project involving recording on metal. To get any further, I feel I need to vastly reduce the size of the tape head or possibly the shape, so it is more like that of a needle. I was planning to experiment with the form of ferrite beads as I have used them in the past to record onto steel wire. However, so I understand the method of recording on a hard drive disk shares the same electromagnetic principles as a tape machine. Perhaps this is a ridiculous idea- I understand the speed of the recording material would have to be vastly increased and sound quality would be an issue- but would it be possible to reconstitute the read/write head of an old hard drive into something that could record sound?
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Re: Is it be possible to use a hdd head to record and play analogue signal/sound?

Postby hobbyist » Fri Aug 02, 2019 12:06 am

Nikulnickel wrote:I have been experimenting using the read/write heads of tape recorders for a project involving recording on metal. To get any further, I feel I need to vastly reduce the size of the tape head or possibly the shape, so it is more like that of a needle. I was planning to experiment with the form of ferrite beads as I have used them in the past to record onto steel wire. However, so I understand the method of recording on a hard drive disk shares the same electromagnetic principles as a tape machine. Perhaps this is a ridiculous idea- I understand the speed of the recording material would have to be vastly increased and sound quality would be an issue- but would it be possible to reconstitute the read/write head of an old hard drive into something that could record sound?

Possible yes. With enough money and time and work.

Feasible no. Totally impractical way to record.

No. HD heads are not allowed to touch the platter. They fly at tiny distances just above the medium in a very dust free environment.
You are more likely to damage the head or the platter if you tried to record audio like a tape machine does.

Now , you could record audio real easy on the HDD by using DIGITAL samples of the analog signal. That is what we all do with our PCs unless you only have the newer SDD.
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Re: Is it be possible to use a hdd head to record and play analogue signal/sound?

Postby Wonks » Fri Aug 02, 2019 6:53 am

Indeed. HDD heads have an incredibly small magnetic head and a correspondingly small magnetic field, meaning they have to be very close indeed to the disc to provide a strong enough magnetic signal to read and write data.

They need to work in that sealed, dust-free environment the HDD enclosure provides.

And that data is just 1's and 0's, which doesn't need a strong signal/noise ratio to work. And it won't be a good ratio; between 22 and 25 dB at best, down to 18dB at worst. Good enough to distinguish a 0 from a 1 (only a 6dB difference) for digital systems, but very poor for analogue.

If you move away from the sealed environment, then the heads have to be moved further away from the medium, resulting in a lower magnetic flux at the medium and a much weaker signal, so an even worse S/N ratio.

And not using a good fine grain metal oxide surface to record onto will also weaken signals and reduce S/N ratios even further.
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Re: Is it be possible to use a hdd head to record and play analogue signal/sound?

Postby Wonks » Fri Aug 02, 2019 7:01 am

I also fear that contact between HDD head and a metal surface would quickly destroy the head as they aren't designed for physical contact.
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Re: Is it be possible to use a hdd head to record and play analogue signal/sound?

Postby Nikulnickel » Fri Aug 02, 2019 11:15 pm

Thank you for your responses. I totally understand that hard drive heads don't touch the platter but then tape recorder heads don't actually need to touch the magnetic material either in order to record if they have enough power, my main aim is to create a working write head at a smaller scale. Since hard drive heads, like tape recorders use a ferrite core to magnetise the material I thought they could be used, but clearly, that would require some work.
Ampex did create an analogue disc video recorder similar to a hard drive in the late 60s called the HS100 : https://www.youtube.com/watch?v=cW7jvmoLQ7o
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Re: Is it be possible to use a hdd head to record and play analogue signal/sound?

Postby Matt Houghton » Sat Aug 03, 2019 10:46 am

Cloud Hills released an analogue delay based on a floppy disk drive a few years back...
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Re: Is it be possible to use a hdd head to record and play analogue signal/sound?

Postby N i g e l » Sat Aug 03, 2019 11:10 am

Nikulnickel wrote:hard drive heads don't touch the platter but then tape recorder heads don't actually need to touch the magnetic material either

Thats right. High speed tape recorders (and HDDs) have aerodynamically profiled heads so that the tape floats above the tape head and the disk head floats above the disk.

"Head crash" is to be avoided :headbang: :angel:
........

Although the HDD electronic data record signal is digital, the magnetic stored level on disc is analogue and can be thought of as the summation of lots of little grains of magnetisim which have varying agility to change polarity...

HDDs didn’t have an erase head so you would be recording Sound-on-Sound.

Something like

New_Recording = 75%New_sound + 25%Old_Recording

[i just made up the percentages for an example]

Not a problem when interpreting the playback digitally but for analogue interpretation,
you would need to erase the disk [several times] before each fresh recording was made.
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