[LAD] recording impulse responses

[Steve Harris]

On 16 Jun 2008, at 22:31, Michael Iber wrote:

> Hello list,
> later that summer I will have the chance to record some impulse
> responses of some ancient technical gear like radios, grammophones  
> etc.
>
> The question is, where to start with the recording chain:
> e.g an IR from the "Volksempfaenger"-Radio: does it make sense to play
> the sweep into an transmitter (of the very same period) and record the
> output with the microphone near the speaker of the radio? Or would one
> prefer to play the sweep diretly to the amplifier of the radio?

Depends weather you want to capture the colouration of the transmitter/ 
receiver or just the amplifier. I can't work out what the crackles  
that you typically get on old radio equipment will do to the impulse  
response, but it may not be possible to capture them.

I seem to remember reading that you have to play the signal in at  
different amplitudes in order to capture the kind of complex non- 
linear responses you'll get from equipment like this.

> How do I get a meaningful IR from a grammophone: start with the  
> needle?
> try to find a vinyl record with a sweep on it?

You should be able to induce the sweep in the coil that makes the  
pickup work, just put another coil near to the one in the gramophone.  
You could use something like a telephone pickup coil and play the  
signal into it. I've no idea what signal strength you'd need, but  
probably not very much.

- Steve