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Logic 9 Re-amping and latency

Discussion in 'Logic 9' started by afavreau, May 20, 2010.

  1. afavreau

    afavreau Senior member

    If I understand correctly, reamping my bass would create latency, right?

    -Is there anyway or technic to correct this latency after re-amping?
    -Any tips on how to re-amp and minimize latency?
    -Also, should I do anything special in order to bring the line level output of my interface to the instrument level of my amp while re-amping or just plug in a 1/4' unbalanced cable?

    Thanks

    Andre
     
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  3. Orren Merton

    Orren Merton Logic Samurai / Administrator Staff Member

    Hi Andre,

    The bad news: yes. Any time you run any signal out of your audio interface and then back into your audio interface, it will need to be converted back into analog audio for your external device, then reconverted to digital on it's way into Logic.

    The good news: The I/O plug-in will compensate for it, so you should be fine.

    What you'll want to do is use Logic's "I/O plug-in" to do your reamping. This is basically like adding an I/O insert patch onto the specific audio track of your bass. And like all plug-ins in Logic, it is is compensated. So here is the workflow I recommend:

    1) Insert the I/O Plug-in in an Insert slot of your clean bass track.
    2) In the I/O plug-in editor, select the audio input and audio output you are using on your audio interface to do your reamping.
    3) Click the "ping" button and the I/O plug-in will send a short signal through your amp and back, to get the exact latency that the process entails so that it can compensate for it.
    4) Play your song, and adjust your amplifier to taste.

    Keep in mind that the I/O plug-in is a realtime, live plug-in. This means that your actual guitar track is always dry, and you continually have to keep your amplifier connected to your audio interface to process the track. If you always want your reamping to be live, this is perfect. However, if you dial in the exact tone you want, and decide that you want to "print" that sound and not reamp live anymore, add the following step:

    5) Solo the bass track and use the Bounce command to bounce the track and add it to the audio bin. You can then add the new bass+amp track to your Arrange.

    Note that you cannot use the Bounce In Place command, as that is an offline function, and reamping happens in realtime.

    Running a low impedance line input into an amp input has the same effect as running an active pickup or a pedal into an amp input. So you should be fine.

    Hope that helps!

    Orren
     
  4. afavreau

    afavreau Senior member

    WOW!!!!!! Awesome! I always wondered what was that plugin for!

    Thanks! I'll go try it!

    Andre
     
  5. Sascha Franck

    Sascha Franck Senior member

    Basically you're right, I think. But I noticed quite some differences when checking out the reamping box of a friend. It doesn't seem to be anything else but an "upside down" DI box, and they're not expensive, either - but seriously, there seems to be a difference. And I'm anything but Mr. Golden Ears.
    Maybe it's more of a difference with passive guitar/bass signals because the impedance may have an effect on the sound - I wouldn't exactly happen to know, but I do know that the difference in that case was easy to spot.

    - Sascha
     
  6. afavreau

    afavreau Senior member

    That's what a friend of mine I trust answered me too:

    The line out will be going into an amp. Assuming there's no ground hum, it'll be close to the output of the bass instrument itself.

    But this also exists: http://www.reamp.com/
    So there must be a reason... I think!
     
  7. Peter Ostry

    Peter Ostry Administrator Staff Member

    So you don't trust my friend Orren's excellent suggestion, spare the headache and just plug the damn line into the amp? :)

    Aha!
    Your fault. Here we go – and don't complain:

    A line output is not exactly the same as a guitar pickup. A passive pickup is a coil around a metal heart, even if you do not play metal. It has a low resistance and loves a high input impedance in the amp. Therefore the amps have normally 1 MΩ input impedance or more. An active pickup is an electronic device, see it as a little preamp. It comes closer to your interface outputs but is still not the same.

    Pickups, stomp boxes and many multieffects are designed to go into the preamp stage of a guitar or bass amplifier. A line output is designed to go, surprise, into a line input. But before we continue, I give you a last chance: Unless you are a technician the difference between the output of a stomp box and your line outputs is not big. You can safely ignore it if you are happy with the tone of your amp when you use it for reamping. Just plug the line in and listen.

    You are still here? Ok. Technically this connection is not correct. Not at all. Your interface has most likely a balanced output but the amp expects an unbalanced input ("mono" cable). Since you do not use one phase in the input jack, or may even shorten one phase to ground, you lose 6 dB. Bad? Not really. You get plenty dB's from your interface to overload the amp.

    To make it correct, you should at least remove the cold phase in the plug or use one mono lead of an Y cable which does the same. And it does not matter which one you use. After reamping you have to check the phase in Logic anyway.

    Second, think if you really need the whole amp. Do you need the preamp stage? Is the preamp why you really love the tone or is it the power amp that feeds the speakers? Many amps have an effect loop and you can also plug your interface into the return jack of that loop or straight into the power amp if there is an input for that. Some amps call it "Monitor" input. All of these connections bypass the preamp. If you need the preamp or the EQ or something else, you want the guitar input.

    Furthermore, with the removal of one phase you cripple the signal, technically. If you don't want that, insert a DI-box between the audio interface and the amp. Beside of a couple of resistors for a pad, a passive DI should have only one component: the transformer. You may know what for a DI-box normally is, you use it to feed an unbalanced signal from one side and get a balanced signal on the other side. But since there are no active parts in a passive DI, you can also use it in the reverse direction to feed balanced and get unbalanced. This is what the amp would expect if he had eyes to see it.

    The crux with a DI-box is the transformer. A cheap transformer may sound interesting, but the very best transformers are preferable because they make the sound good or even better. If you want a really good passive DI-box, ask for the name of the transformer. If it is Lundahl, Haufe, Carnhill or some other big name, grab it instantly, regardless how the case looks and who sells it. Remember, neither the eyes of your interface nor the eyes of the amp are good enough to see what you are doing. But they feel it and finally you hear it.

    Just a side note: if you get some hum while reamping and cannot remove it otherwise, a DI-box may also help.

    Finally, feeding the amp is the easier part of reamping. To get a really good sound you need also one or two good mics and the proper recording technique. I my opinion this is more important than discussing the type of plug.


    This is a DI-box with a potentiometer. They are proud of their transformer and if it is good, they are right. The other listed features are marketing slipslop.

    ---

    Now, what do you say? Wouldn't it have been easier to just plug the thing in and listen to the output? ;)

    I myself use for all high quality un-balancing a passive DI-box with a Haufe transformer and I am happy with it. And high quality is relative in this case. I had so many effect boxes and synths which grabbed and spit all flavours of noises that I just take a box and don't think about the problem anymore.
     
  8. afavreau

    afavreau Senior member

    Wow! Very interesting! I sure learned a lot!

    But now you that got me hooked, I have to ask you if you could explain this a bit more... :eeek:

    To get a really good sound you need also one or two good mics and the proper recording technique. In my opinion this is more important than discussing the type of plug.

    I only have an AKG D112 to reamp my bass.

    Also, the reason I'm reamping is because I only have a single room to do everything and we will be three guys recording at the same time. So I want to avoid leaking. So you are right, I may not need the pre-amp stage when re-amping.

    Oh yeah! By the way, I do trust Orren, that's why my comment was kind of confirming his.

    Thanks
     
  9. afavreau

    afavreau Senior member

    Peter! So I've been reading your post a couple of times and just to make sure...

    If I use a passive direct box, I don't need to remove the cold phase in the plug or use a mono lead of a Y cable, right?

    Thanks
     
  10. Peter Ostry

    Peter Ostry Administrator Staff Member

    Well, allow me to do a step back. I am no great recording guy, here are far better people in the forum. But apart from the mic choice the placement and the distance are crucial. With guitar cabinets, the more you go to the middle of the speaker, the brighter gets the tone. Far on the side it becomes first kinda smooth, then dull. I think this must be similar with a bass amp. Furthermore, cabinets are often close miked but this is not always the best choice. Is it a good choice for a bass amp? I don't know. But the wave of a bass tone can be 6 meters or so. If the room is acoustically good, there might be a better place for the mic than directly at the speaker.

    The second reason is that you can decide how you want the guitar in the mix. Reamping with the right sound is better than too much EQ or compression.

    This was just a suggestion to think about. The preamp makes a lot of the sound. I guess you don't want it if you recorded through this preamp. But it really depends on the situation. I don't reamp through bass cabinets, so I don't have experience with that. I use a Sansamp RBI.


    Right.

    Using only one phase is not a bad thing though. But un-balancing with a transformer is the "clean" way.
     
  11. afavreau

    afavreau Senior member

    Peter,

    Just by curiosity, I also have a FireFace 800 like you. Do you think the unbalanced stereo output could provide an interesting solution to go to an Amp?

    Also, I'm not contradicting you at all here, but I found this on http://www.reamp.com/faq.html. I'm curious, what do think? Here it is:

    Question - Some people say I can use a passive direct box in reverse for reamping. Is this true?

    Answer - – No. This would not work because of the large level differences between a microphone level signal and a line level signal. On the direct box the instrument input is designed for instrument level signals (-20dbm) and the microphone out is designed to give a microphone level signal (-60dbm typical) using a direct box in reverse would put a +4dbm signal into a –60dbm output and would cause extreme signal distortion before you even plugged into the amp.


    Thanks
     
  12. afavreau

    afavreau Senior member

    On the FF800, there is also the possibility of setting the output at HI GAIN, +4 dBu or -10 dBV?

    Which one should I choose?

    Thanks again
     
  13. Peter Ostry

    Peter Ostry Administrator Staff Member

    No. You would also need an adapter cable because you want only one channel.


    The answer is wrong. It does definitely work. A passive DI-box does not know about signal levels. The transformer has two separate coils of copper wire and that's it. You are the one who sets the level.

    He may talk about transformers with high ratios but the output level depends on the input level. If the box gives you too much, turn the output of the DAW or the interface down or, if it is better, turn the input of the amplifier down. Or do both, whatever is good for the sound.


    I think he talks about transformers with high ratios. However, the input level for the transformer ist still under your control.


    Sorry, but this sounds like "you cannot use a fork for eating because it would damage the table"... Nobody sends a high line level to the instrument input of an amp, DI-box or not.


    Here is some information:
    http://en.wikipedia.org/wiki/Re-amp
    (scroll down to "Electronic Interfacing")


    And here is a short test:

    To simulate the stuation as good as possible I took the Logic Test Oscillator and sent 1 kHz sine and square waves with –12 dB to the outputs 7-8. On the interface I cabled output 7 directly to input 1 to get the direct signal back. Output 8 went through a reversed passive DI box to input 2. The only difference to reamping was, that I simply plugged the unbalanced output of the DI-box into the interface's line input. In real live the signal would come through a microphone. But the setup is quite fine to compare the direct signal to the output of a DI-box.

    And here comes the interesting part, the oscillograph ...

    First a Millenium DI-Box. The brand is known for cheap stuff but this box has an extraordinary good transformer:
    [​IMG]
    [​IMG]
    From the identical readouts above you may think that the box isn't working or I did something wrong but no, below is another box, from Cordial:
    [​IMG]
    [​IMG]
    The output of the reversed Cordial is higher. But apart from the difference in output level, where is this "extreme signal distortion" that the guy mentioned? It is not here because it does not happen when you supply the right input level.

    Note:
    What you see as increased signal level from the Cordial DI, corresponds to a similar drop when you use the box in the normal direction. If you plug something into the unbalanced input, the Cordial box gives you about –6.5 dB less output. This is a bit low but ok and this box sounds good. On the other hand, the box with the Haufe transformer works 1:1. And it sounds better. But it is not the ratio alone. I am not a technician and cannot explain why some transformers sound good and some less good. But it is the crucial part in a passive DI-box. So, if you want a really good one, get one with a good transformer. That's the only thing that counts.


    If you have standard studio gear with balanced lines set the Fireface input and output to +4 dB which is the usual studio level.
     
  14. afavreau

    afavreau Senior member

    Wow!

    The only thing a Reamp Box does for you is add a potentiometer, but if you are careful, you can simply ajust the interface's output going to the reverse DI (as we always do when recording) and you'll be fine.

    Radial seems to confirm what you say, though still trying to make a reamp box a valid product.

    Q: What difference is there, if any, between using the JDI or ProDI
    in reverse for re-amping versus using the ProRMP?

    A: The ProRMP is equipped with a +4dB balanced line-level input designed to accept a signal from a mixing console or recorder while the JDI or ProDI wants to 'see' a -60dB mic level input so that the transformer will not be saturated. If you are careful, you can use a DI backwards... the ProRMP is designed to be easier to use.


    So a reamp box just makes things "easier", like wearing a bib makes it easier to eat spaghetti, but in the end, it's the exact same spaghetti that you eat, not one little difference as you have shown (if you have a good transformer in your DI).

    A potentiometer is just a nice little feature to a passive DI when you use it in reverse.

    Thanks Peter. I really appreciate it! It was fun! I'll try to find a good passive DI with a Lundahl, Haufe or Carnhill transformer now. Any suggestions are welcomed...
     
  15. Peter Ostry

    Peter Ostry Administrator Staff Member

    Radial is obviously more honest than the other guys.

    Three simple steps after you have connected the reversed DI box:
    1) Pull the output fader in Logic fully down.
    2) Set the input gain on the amp as you would for a guitar.
    3) Start the playback and slowly move the output fader up until the amp is as loud as a guitar would be. If you are not sure, compare with a guitar.

    That is all, no need to be any more "careful". If the amp is normally loud with a normal input gain, you deliver a normal level. Transformer saturation and all this stuff is not something you can easily control, so take a good transformer, deliver a proper level and you are set. Then try to play with a lower or a hotter input and adjust the gain knob on the amp to get the sound you expect.

    And well, many people just plug the interface into the amp and it works also ...


    Jensen is another famous name. I believe this is what Radial uses.
     
  16. aramism

    aramism New Member



    hope you guys still get this as it's 4 years later but here's my question:

    I'm trying to do something similar except not reamp but print outboard processing like compression and eq during a mix. I use the IO plug in already to process the track that needs processing but want to print that for easy mix recalls in the future.

    I am also using analog summing so I have a "return" track constantly on input monitoring and when I bounce the mix I just hit record on that track.

    My concern is making sure things line up when I put the file back. What is the best way to go about this?
     
  17. Peter Ostry

    Peter Ostry Administrator Staff Member

    You don't need to line things up. In Logic you can record from a bus. Go to a channelstrip that has one or more I/O plugins, make a 0 dB send or set the output of the strip to a bus, and use this bus as input for a new audio track. After recording you can switch the "old" channelstrip off and use the recorded track instead.

    If you have other plugins before and after the I/O plugin, recording the whole channelstrip will of course reduce your recall possibilities. Post effects (after the I/O plugin) aren't a problem because you can disable them while recording and afterwards copy/drag the plugins from the former "hardware channelstrip".

    The handling of pre effects (before the I/O plugin) can get complicated. You may just see them as part of the hardware and record them together with the hardware. If you do not want this, you may put them onto an earlier stage which is not always possible.

    My personal preference is not to use any effect plugins before an I/O plugin in the same channelstrip. If I have to, these effects count as hardware and get bounced. I don't always need or want total recall.
     

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