Post by ashcatlt on Jun 24, 2010 18:04:46 GMT -5
I’ve made similar posts re: this issue on a couple of other forums in the last few days, so I thought I’d just go ahead and cross-post here too.
We’ve talked about re-amping around here before, but there we were discussing what it takes to go from the recorder to the amplifier. Here I’m talking about the other end of the process – capturing a guitar sound appropriate for re-amping.
If we want to get the most authentic tone out of a re-amp situation – as close as possible to the sound of this guitar plugged into this amplifier – we want to record something as close as possible to what would be present at the input of the amp. After we’ve chosen the guitar, decided which pickup or combination we want to use, set the guitars controls (V and T) appropriately, and chosen our cable, it comes down to the input-Z of the device into which we are plugging.
From what I’ve seen, most active DI’s – whether standalone or built into a mic pre or interface – present a nominal 1M impedance. This is a bit higher than many typical guitar amps. Many tube amps especially will have something like 470K or so.
Passive DI’s, on the other hand, do not have an impedance of their very own, but rather reflect the impedance from whatever is on the other side. Plugged into a transformer-based DI, the pickups “see” some multiple of the mic-pre’s input-Z. This can often be a bit lower than what would be expected at the input of an amplifier, especially when we’re using the passive split feature to monitor through an amp during tracking. The input-Z of this amp will be in parallel with the reflection of the mic-pre, making it even lower. This is often a good thing when we intend to use the DI track as is in the mix, but may not be quite appropriate for re-amping purposes.
So, how to “fix” this? A DI or buffer with variable input-Z would be ideal, but how many of us have one of those lying around?
For the active DI, all we really need is to put an appropriate resistance in parallel with the input. I’ve got a cable with a 1M resistor wired between the tip and sleeve right inside the barrel of the plug. In parallel with the DI input it ends up at 500K, and that’s close enough to 470K for me. One could also use a passive splitter (Y-cable, etc) to connect the guitar to two 1M inputs with about the same effect.
Most passive guitars come conveniently equipped with a resistance to ground, and it’s even variable. It’s called the Tone Control. It should be possible to just roll this knob back a little bit to emulate a bigger load (lower input-Z), and it’ll do in a pinch, but I can think of a number of reasons why this might not be the ideal solution.
For the passive DI it’s a little more complicated. We need to put some hi-Z active stage between the guitar and the DI. Just about any non-true-bypass pedal in bypass mode will give us 1M. From there we might need to knock it back down as with the active DI above. At this point we start to wonder why we’re not just using an active DI to begin with…
This also points to another important thing to keep in mind: all that matters here is the first active stage after the guitar. If you’re running through even one pedal along the way, everything I’ve said above is moot.
Now watch me as I step way out onto a limb. All we’re really talking about here is a low-pass filter. Specifically, the filter created by the interaction between the internal components of the guitar with the capacitance of the cable and the input first active stage. Most of us do have other filters – hardware or software - which we could conceivably use to massage and fine tune the response after the track is recorded to get the best response out the re-amped signal. If we don’t know for sure at the time of tracking exactly what we’ll be re-amping through, I’d tend to lean toward capturing as much of the “treble” as possible initially. Yes, I know this won’t be exactly the same, and borders on blasphemy, but you don’t have to tell anyone!
We’ve talked about re-amping around here before, but there we were discussing what it takes to go from the recorder to the amplifier. Here I’m talking about the other end of the process – capturing a guitar sound appropriate for re-amping.
If we want to get the most authentic tone out of a re-amp situation – as close as possible to the sound of this guitar plugged into this amplifier – we want to record something as close as possible to what would be present at the input of the amp. After we’ve chosen the guitar, decided which pickup or combination we want to use, set the guitars controls (V and T) appropriately, and chosen our cable, it comes down to the input-Z of the device into which we are plugging.
From what I’ve seen, most active DI’s – whether standalone or built into a mic pre or interface – present a nominal 1M impedance. This is a bit higher than many typical guitar amps. Many tube amps especially will have something like 470K or so.
Passive DI’s, on the other hand, do not have an impedance of their very own, but rather reflect the impedance from whatever is on the other side. Plugged into a transformer-based DI, the pickups “see” some multiple of the mic-pre’s input-Z. This can often be a bit lower than what would be expected at the input of an amplifier, especially when we’re using the passive split feature to monitor through an amp during tracking. The input-Z of this amp will be in parallel with the reflection of the mic-pre, making it even lower. This is often a good thing when we intend to use the DI track as is in the mix, but may not be quite appropriate for re-amping purposes.
So, how to “fix” this? A DI or buffer with variable input-Z would be ideal, but how many of us have one of those lying around?
For the active DI, all we really need is to put an appropriate resistance in parallel with the input. I’ve got a cable with a 1M resistor wired between the tip and sleeve right inside the barrel of the plug. In parallel with the DI input it ends up at 500K, and that’s close enough to 470K for me. One could also use a passive splitter (Y-cable, etc) to connect the guitar to two 1M inputs with about the same effect.
Most passive guitars come conveniently equipped with a resistance to ground, and it’s even variable. It’s called the Tone Control. It should be possible to just roll this knob back a little bit to emulate a bigger load (lower input-Z), and it’ll do in a pinch, but I can think of a number of reasons why this might not be the ideal solution.
For the passive DI it’s a little more complicated. We need to put some hi-Z active stage between the guitar and the DI. Just about any non-true-bypass pedal in bypass mode will give us 1M. From there we might need to knock it back down as with the active DI above. At this point we start to wonder why we’re not just using an active DI to begin with…
This also points to another important thing to keep in mind: all that matters here is the first active stage after the guitar. If you’re running through even one pedal along the way, everything I’ve said above is moot.
Now watch me as I step way out onto a limb. All we’re really talking about here is a low-pass filter. Specifically, the filter created by the interaction between the internal components of the guitar with the capacitance of the cable and the input first active stage. Most of us do have other filters – hardware or software - which we could conceivably use to massage and fine tune the response after the track is recorded to get the best response out the re-amped signal. If we don’t know for sure at the time of tracking exactly what we’ll be re-amping through, I’d tend to lean toward capturing as much of the “treble” as possible initially. Yes, I know this won’t be exactly the same, and borders on blasphemy, but you don’t have to tell anyone!
