Axe-Fx II connections and levels
From Axe-Fx II Wiki
Front input secret sauce
- The front panel input (INSTR) uses a proprietary circuit and a dedicated A/D converter to lower noise ("secret sauce"). It's conditioned for guitar through hardware and software. For best results use the front input for guitar, whether wired or wireless, electric or acoustic (except when running a line level signal). The front input also has a soft clip function.
- Cliff's comments:
- "You have to set the input selection to match the input you're using. If you're using the front input then you must set the input selection to front and vice-versa. If you plug something into the front and set the input selection to rear it will get MUCH brighter. The front input is optimized for guitar level inputs and has spectral shaping and more gain than the rear input. The front input is optimized for guitar pickups. This is a combination of hardware and software processing. If you set the input source to Analog Rear this turns off the software processing part. If you are plugged into the front it will change the tone since you're still going through the hardware processing. This is why I say you must match the input selection to the input you are using. The rear inputs are standard line-level inputs and can be used with any program material. The front input, as stated above, is optimized for guitar pickups. As such it has more gain and less headroom and may clip if used for non-guitar program material. If you plug a guitar directly into the rear you may find you don't have enough signal level."
- "The spectrum of a guitar is pink(ish). Above 800 Hz or so the energy rolls off dramatically. As luck would have it, humans perceive noise above 800 Hz or so to be most objectionable as it manifests itself as hiss. So the front input pre-emphasizes the high frequencies and then does the inverse in software. This has the net effect of a flat frequency response but pushes the noise floor down by the amount of the pre-emphasis. It's an old trick, used in FM radio and vinyl records. The basic premise is to optimize the data conversion to the information content of the source."
- "A buffer (in front of the Axe-Fx II) will render the impedance stuff ineffective. It will also add (maybe considerable) noise which may defeat the low-noise advantage of the front input." source
- The Axe-Fx II XL and XL+ feature “Secret Sauce III”. Cliff: "The "Special Sauce III" uses a combination of things to get a lower noise floor. One of these things is new, premium Burr-Brown op-amps in the signal path which have extremely low noise and distortion (and are very expensive). As always I don't design stuff to be cheap, I design it to be good." source
- "The XL+ front input circuit is identical to the AX-8 except the AX-8 doesn't have the variable impedance circuitry." source
A/D Input Level
- Level in I/O > INSTR IN does NOT affect amp gain, volume level or output clipping! It optimizes the signal-to-noise ratio only. This is different from the Axe-Fx Standard/Ultra. For more information about output clipping, see Preset output level.
- Adjust INSTR IN to make the red input LED blink occasionally while strumming. Then turn it down a bit again to make it blink only occasionally ("tickle the red"). There's quite a range between orange and red. If you can't make it blink red, don't worry, but do check the status of Input 1 Mode (see below).
- The red light turns on BEFORE the front input clips. It means "Warning, you're approaching clipping" as opposed to "Warning, you ARE clipping". Red light turns on at -6dB of the point where the signal is hard limited / clipped.
- Cliff's comments:
- "For a Strat, near 100% on the input level is not unusual. I run my Strat around there. It has vintage-type pickups." source
- "To get the best noise performance it is important that the Instr In trim is set correctly in the I/O->Input menu. Set this as high as possible without clipping the input." source
- "You don't HAVE to tickle the reds. Adjust for your hottest guitar and leave it." source
- "The AFXII has digitally controlled potentiometers before and after the A/D and D/A converters. Therefore it knows what the input and output gains are. It compensates for these gains in the digital path." source
- "Full-scale is a term that indicates the maximum signal level into or out of an A/D or D/A converter, respectively. With digital converters the best performance is achieved by operating the converter such that the nominal signal level is close to full-scale. The exact voltage is unknown and irrelevant. Most digital gear will have indicators that measure the levels relative to the converter's full-scale value. For example, the input meters on the Axe-Fx indicate the input signal relative to the A/D converter's full-scale value. The "tickle the red" advice aims to operate the A/D converter near its full-scale value as the red LEDs light at 6 dB below full-scale, or -6 dBFS." source
- Tutorial by AxeFxTutorials.
Input 1 Mode: Left / Right / Sum L+R
- When using a guitar in the front input, set Input to Left (not Sum L+R). Using Sum L+R can introduce noise (from the disconnected right Input 1) and attenuates the signal level (6 dB).
USB source and USB Level
- If you're using Input 1 at the rear and not the front, set the input source to “Analog Rear” (I/O). When using the front AND rear input, set it to "Stereo".
- Rear Input 1 has the same impedance as the front input (1 Mohm, for guitars) but it operates at LINE level instead of instrument level.
- The front input does not disable Input 1 left at the rear (different from Standard/Ultra). Use the menu to select either the front input or Input 1 (rear). You can leave everything plugged in.
- If you connect a microphone level source to Input 1 or Input 2 at the rear, there will be a level mismatch. You'll need to increase the signal level (or use a DI or mic preamp) to get sufficient signal strength.
- If the rear input has much less noise than the front input, it's possible that there's a hardware issue with the front input.
- Cliff's comments:
- "There is a sensor on Input 2. If you unplug the cable from it the FX Loop will not run." source
- "Input 1 on the rear is a very high impedance input (1 Mohm). It is compatible with low impedance outputs. Most people don't understand the real meaning of impedance and think you need to connect low impedance to low impedance but that's only with passive devices and is a relic of the old days when transformers were used to get the best power transfer. Nowadays we have active inputs with very high impedance which are compatible with a broad range of source impedances." source
Use with multiple instruments
- To set up the Axe-Fx for use with two instruments:
- Set Input 1 to Stereo in I/O.
- Connect one instrument to the front, and the other to rear Input 1 Right.
- Use two rows on the grid.
- Add a VOL block to each row. Set one to Input left (for the instrument that goes into the front input or rear input 1 Left) and the other to Input Right (for the instrument that goes into rear input 1 Right).
- Add an AMP block after each VOL block if necessary. You can also leave out the VOL blocks and set Amp 1 to Input Left, and Amp 2 to Input Right; this only works with the Amp blocks in the first column.
- Continue the rows to the end, adding a CAB and effects to each one if necessary, or merge them if desired. Keep the signals separated by using Balance controls.
- Also see this thread and this thread and this thread.
- Solution for connecting 3 instruments to a single Axe-Fx.
- Youtube tutorial.
Use with different guitars
- A preset may require adjustment when changing guitars. Here are methods to deal with this.
- IN/GTE > LEVEL: this parameter controls the loudness of the signal entering the grid. It was specifically introduced for this purpose: compensating output level differences between guitars. It works per preset only, so it needs adjustment per preset, unless the setting is stored as part of a global block. No possibility to attach a modifier.
- AMP X/Y: use different values for Input Trim in X and Y.
- Two AMP blocks.
- SCENES and SCENE CONTROLLERS: attach Input Trim in the Amp block to a Scene Controller. In the Controllers menu set the controller to the desired value for each scene. Switch scenes when switching between guitars.
- GLOBAL AMP GAIN.
- BLOCK: add a low-CPU block to every preset. Like FILTER or VOL or PEQ (PEQ and FILTER allow additional EQ-ing). Put it at the start of the grid to make it affect the amount of gain in the Amp block. Keep the block neutral and set its Level at i.e. -6 . Make it a global block, so you can easily change a setting and have it applied across all presets immediately. Attach its Bypass parameter to an external controller. Engage this block by going into I/O > MIDI and toggling EXT CTRL xx INIT VAL between 0% and 100%. Or assign a general function footswitch to the external controller’s CC and use that for toggling instead (set the switch to Global:Yes in the MFC). It works across all presets.
- Wicked Wiki: Settings for Different Guitars.
Use with acoustic instruments
- The front input can be used to connect an acoustic instrument.
- The IR of an acoustic body can add acoustic resonance to the tone. There are no acoustic IRs among the stock cabinets in the Axe-Fx II. You can find some here:
- Stick to the highest IR resolution when using acoustic IRs, Ultra-Res if possible.
- Presets for acoustic guitars with good pickups can be simple: compressor, EQ, reverb. An AMP block is not required but TUBE PRE can help to warm up the tone.
- This thread contains a nice clip and preset for a piezo-equipped guitar.
- Alternatively: use Tone Matching. Tutorials on G66.eu.
Use with bass guitar
- The Axe-Fx II provides stock bass cabs and some bass amp models.
- The tuner supports bass guitar tuning.
- Bass tone tutorial by Jon Symons' Sonic Drive Studio.
Use with external stomp boxes
- If you want to use an external analog or digital pedal with the Axe-Fx II, connect it between the guitar and the Axe-Fx. Remember to check Input impedance on the Axe-Fx II.
- The Axe-Fx II lets you insert a device somewhere in the routing using FXL / Effects Loop. The effects loop connections (both IN and OUT) operate at line level, so adjust levels to compensate. See FXL / Effects Loop.
Use with a wireless connection
- Connect a wireless receiver in the same way as a guitar: to the front input. This takes advantage of the front input's "secret sauce" for noise reduction. The rear inputs (both 1 and 2) operate at line level and are less suited for use with most wireless receivers.
- Cliff: "The front input has a better SNR but if you are using a wireless the better SNR of the front input won't be noticeable since the noise of the wireless will dominate." source
- It's as easy to get your guitar to feedback with the Axe-Fx II (when monitoring through a monitor or speaker) as it is with a regular amp and cabinet. If you don't succeed, experiment with the Output Phase parameter in the I/O menu.
- Cliff: "I did some studies years ago and having a speaker in proximity to the guitar actually changes the final tone considerably. I compared the frequency response with the amp in isolation to the frequency response with the amp in proximity and measured several dB difference in the lows and mids. It was clearly audible when the recordings were played back." source
- There's no dedicated "sustainer" or feedback effect in the Axe-Fx II. Forum member Simeon created a feedback simulation preset, mimicking controlled feedback.
Hiss without a connection
- When nothing is connected to the front or rear inputs, there may be some hiss.
- Cliff's comments:
- "Optimal gain staging would be with the level knob around noon. Higher than this and you risk clipping the inputs of the downstream device. With the level knob at full the Axe-Fx II will probably incinerate a Soundblaster or other low-cost stuff. The max level out of the Axe-Fx II is +20 dBu. Most pro gear can easily handle that but lots of gear cannot and the trend in newer gear is towards lower and lower maximum input levels (due to single-ended designs and low-voltage/low-power constraints). In the old days, +20 dBu was routine. Everything could put out and handle +20. Not so much anymore." source
- "The II actually has more output than the I. The II can do about +20 dBu, the I was about +18." source
- "Start with amp volume at noon. Bring up Axe-Fx volume until desired level is reached. If you need more, turn up amp. With the Axe-Fx volume all the way up you would be pushing +20 dBu into the amp which could clip the inputs to the amp." source
- Both XLR and 1/4" jack cables can be used to connect the Axe-Fx II's outputs to other equipment. These are line level connections. More information.
- Cliff: "All outputs are +4 dBu. Please see the manual for full I/O specifications." source
Simultaneous use of XLR and 1/4" outputs
- The XLR and 1/4" jack outputs can be used simultaneously to feed different devices.
- Cliff: "Both outputs should work simultaneously. They are actually buffered so even if you shorted one it shouldn't affect the other." source
Front panel level knobs
- Cliff's comments:
- "To place a pot after D/A requires running cables to/from the front panel. These cables can degrade signal quality and pick up noise. The pots on the front panel of the II are remote controls for the digital pots. The signal never passes through them. The digital pots also allow us to boost the level from the D/A and then attenuate it precisely to improve output SNR. The Ouput X Boost/Pad feature would be impossible without digital pots." source
- "Flutter noise when turning the level knobs is normal. The output "pot" is actually a ladder of discrete resistors that is remotely controlled by the knob on the front panel. Other products simply reduce the digital signal going into the D/A converter but this is sub-optimum as you reduce your dynamic range when doing this. The Axe-Fx II strives to keep the signal into the D/A as high as possible for optimum dynamic range and then controls the output level using a programmable output gain. The downside of this approach is that you will hear a small noise when the output switches between the resistors in the ladder." source
No DI needed and don't use MIC inputs on the mixer
- There's NO NEED to use a DI-box to connect the Axe-Fx II to a mixer or FOH snake.
- Always connect the Axe-Fx II to a LINE LEVEL input on the mixer. The output signal, balanced or unbalanced, is too hot for a MIC input.
- Cliff: "The XLR output is balanced but it's +4 dBu nominal. The problem is people connect it to a mic input which is way too sensitive for that level signal. If the board has a mic/line switch you want to set it to line level. Or if it has a pad switch turn that on. Otherwise turn the level knob way down. The thing to remember is that XLR is just a connector. It doesn't imply microphone levels. Most pro stuff like eq's, etc. have line-level XLR's."
- If only MIC inputs are available on the mixer, do this:
- Decrease the output level from the Axe-Fx II, f.e. by turning the Global EQ Gain down or by turning down the Output knob at the front.
- Or: use a DI-box to turn the line level signal into mic level. Use a stereo DI when using left and right outputs.
- Or: use a pad switch on the mixer to attenuate the incoming signal and prevent clipping.
Left/right output level differences
- Cliff: "It's inevitable that there will be mismatch in the L/R levels. The output levels are controlled by a stereo potentiometer. The tracking between the two resistors will never be perfect and gets worse as you get near the start of the curve (fully CCW). It's impossible to fix in software as the mismatch will vary from unit to unit. Also, you can't simply put a global balance control because the mismatch varies with the level knob position. The good news is this is one reason why they put faders on mixing boards. I'd hardly consider it a problem or a flaw. Simply compensate as necessary."
Phantom power protection
- Cliff: "There are blocking capacitors on the XLR outputs so you should be fine." source
- To obtain unity gain (input level = output level) when using the effects loop, set both Output Level knobs to maximum. If you would then fill the grid with shunts, you'll get exactly the same signal which you put in. (This is different from the Standard/Ultra which are louder than unity gain.)
- Unity gain is useful only when using the Axe-Fx II in a 4CM setup! In other scenarios there's no reason to crank the Output Level knobs by default.
- Cliff's comments:
- "Unity gain mode is a special mode designed for use with the 4CM. When you turn the output levels all the way up whatever you put in you get out (assuming all unity-gain blocks in the chain). If you have an amp block in the chain then you have tons of gain and therefore no longer have unity gain." source
- "With the Axe-Fx volume all the way up you would be pushing +20 dBu into the amp which could clip the inputs to the amp. Unity gain mode is only desirable for 4-cable-method." source
Multiple output signals
- The Axe-Fx II lets you send multiple output signals. For example, Output 1 is stereo and goes directly into a mixing table (signal with cabinet modeling), while Output 2 is mono and feeds a FRFR monitor or a real amp or power and a guitar cabinet (signal without cabinet modeling).
- Echo Out2 = Out1: enabling this setting in I/O will duplicate the Output 1 signal through Output 2. The Output 2 EQ (Global menu) lets you tailor the tone (independent of Output 1). The Output 1 knob at the front controls the level of Output 1, the Output 2 knob does the same with Output 2. This method DOES NOT WORK with presets that contain a FXL block (effects loop).
- FXL block: insert a FXL block and make it part of the routing (in series or parallel) but don't connect it to the grid output. The signal before the FXL block is sent to Output 2. This method is more flexible than the one above because the position of the FXL block determines which part of the signal is being sent. For example, placing FXL before or after a Cabinet block determines whether the Output 2 signal includes cabinet modeling or not.
Among the last presets in Bank C is a template for sending a signal to FOH (with cab simulation) and a signal to an external amp and cabinet (no cab simulation).
- Left and Right: split the signal at the end of the grid into a row with Cab and a row with a shunt. In the Output Mixer pan those rows 100% left (Cab) and right (shunt). Now OUT1 Left is the signal with cabinet modeling, and OUT1 Right is the signal without cabinet modeling. source
- FXL / Effects Loop.
Routing Input 2 to Output 2
Output level control through MIDI
- MIDI CCs 11 and 12 control the levels of Output1 and Output2.
- To reset them without the help of a MIDI controller, change the assignment to "none" in I/O.