[sdiy] Bubble memory analog delay?

[cheater00 .]

On Wed, Jul 10, 2013 at 12:59 AM, Richie Burnett
<rburnett at richieburnett.co.uk> wrote:
>> Note - magnetic tape domains don't reflect the
>> signal they represent in their degree of magnetization, either. The
>> domains are created artificially with the bias oscillator.
>
>
> The analogue signal being recorded _is_ represented by the degree of
> magnetisation.  However, due to magnetic hysteresis (a type of non-linear
> behaviour,) a bias oscillator is employed to try to linearise the response.
> The key difference is that with audio tape the signal only gets mangled once
> by what's left of the non-linearity during the recording/playback process.
> If you try to shuffle analogue "bits" down a magnetic delay line I think the
> cumulative non-linear effects will quickly wreck your analogue signal.  I'm
> open to being proved wrong of course, if you try it!

Yeah I wonder. The thing is, the bubbles don't get read off in one
spot and recorded in another - they actually move within the magnetic
medium.

>> How do you mean? Just DAC -> DRAM -> ADC? Something like that?
>
>
> ADC -> RAM -> DAC

Errr, yeah :^)

> The RAM addresses are generated by a digital counter that you can clock from
> a fixed or variable oscillator as you wish.  You should be able to find
> examples of digital audio delays using either SRAM or DRAM chips on the
> internet.

Good idea.

> You usually have to take special precautions to periodically refresh DRAM
> (every few milliseconds,) however for a digital audio delay where all the
> rows are accessed sequentially anyway, this can serve to provide the refresh
> function automatically.

I think that's solved with SRAM. Those cost more though.

Cheers,
D.