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 Simulating tape delays
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yenorom Member |
posted 10 January 2006 07:14
 
Hi I'm looking to built an emulation of a tape delay in Kyma, I'm following instructions posted to the Nord modular G2 forum by Rob Hordijk, his solution involves putting an allpass filter into the delays feedback path to rolloff more of the high frequency signal on each pass through the feedback path. Is this how the allpass option works on the delay in kyma or is the allpass filter in the signal path before or after the actual delay? IP: Logged | |
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SSC Administrator |
posted 10 January 2006 08:48
Let's see, if I am remembering correctly, a simple tape delay (one machine) is due to the distance between the Record and the Playback heads. If you take an AudioInput and feed it into a DelayWithFeedback (w/zero feedback); then feed the AudioInput and the DelayWithFeedback into a Mixer, you should get a simple delay with the feedback coming through the air. If you do need to roll off high frequencies, maybe a LowpassFilter or a ShelvingFilter could be inserted between the AudioInput and the delay? Not sure why he was suggesting an AllPass (maybe that was to simulate flanging??) Could you describe your basic signal flow path? IP: Logged | |
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yenorom Member |
posted 10 January 2006 09:02
At the moment I don't have much of a signal flow to describe, this was more of a before I get started question. I'm planning on using a delay module with 0 feedback value and building the feedback path using mixers and a feedbackInput/Output pair so I can put the allpass in the feedback path. As for why use an allpass, from Rob's instructions "What an allpass filter does is pass all frequencies at nearly unity gain, but shift each frequency a little in phase, and thus in time. This phase shift is not like a 'linear time shift', but is a 'near zero' phaseshift for low frequencies to a 'near 180 degree' phase shift (inverting the signal) for high frequencies. The effect when an echo repeat is repeatedly send through an allpass filter is that the echo gets a little less bright on every time it repeats, which sounds quite natural. Using a lowpass filter takes away lots of the high on the first repeat, but hardly more on the following repeats. So this last one sort of goes like piew-pow-pow-pow-pow. Which is not what a real tape echo does, as a real tape echo has no filtering in the feedback loop apart from the tape-damping caused by the rerecording of the repeats on the tape." The patch he built on the G2 using these techniques does have the same sound as an old tape delay. IP: Logged | |
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keph Member |
posted 10 January 2006 10:22
the attached sound displays some of the principles you are referring to. i wasn't out to create a tape delay per se but more just a delay that had some character to it. i used an envelop follower to control a lowpass filter along with an allpass filter. you'll want a saturation stage as well. you'll have to adjust the gain stages so you don't have delay line that easily blows up. IP: Logged | |
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SSC Administrator |
posted 10 January 2006 10:34
In that case, I would put an Allpass module (the general filter module with Allpass checked) between the input and the delay. (If you have no feedback set in the delay itself, then it would not be doing any filtering--at least not by itself without adding the undelayed signal to the delay's output). Eager to hear your results! [This message has been edited by SSC (edited 10 January 2006).] IP: Logged | |
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yenorom Member |
posted 10 January 2006 10:38
Thanks for the help folks, I'll post my results when I've tried out some experiments. Keph thanks for the sound, I'll check it out tonight. IP: Logged |
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