Keeley Halo

Howdy Folks!
I have read through most of the comments and analysis and its truly been a delight. The Halo sound developed from what Andy Timmons showed us he enjoyed, namely the Strymon Timeline and Memory Men, and discussions about how he wanted the sound characteristics to improve. Craighton Hale developed the schematic and circuit board and Aaron Tackett was the DSP programmer. After reading this thread I thought it would be best if we gave a very transparent and revealing description of our process, especially since there were so many creative approaches in trying to replicate the sound. So, I asked Aaron to produce a block diagram of the Halo effect.
Enjoy!
rk

[text from the pdf attached file is copied below]
The input signal is ran into a non-linearity for saturation control and then
low pass filtered. The cutoff frequency of the filter is dependent upon the
amount of saturation, ranging from 2725Hz to 8750Hz.
The saturated and filtered input is ran into Del1 which has a delay time

ratio of 0.75:1 to Del2. The output of the delay is ran through two single-
order filters, an HPF ranging from 0Hz to 300Hz and an LPF ranging

from 1000Hz to 8750Hz.
The filtered output is then modulated up to 9ms at full depth. The left
Del1 is modulated using a cosine while the right Del1 is modulated with a
sine lfo whose rate ranges from 0.1Hz to 10Hz. This modulated output
is then scaled by the feedback control and fed back to the input of Del1.

The saturated and filtered input is combined with the Del1 output. The
sum of these signals’ phase is changed by 180 degrees and ran into
Del2. The output of the delay is ran through two single-order filters, an
HPF ranging from 0Hz to 300Hz and an LPF ranging from 1000Hz to
8750Hz.
The filtered output is then modulated up to 15ms at full depth. Del2’s lfo
is based on the rate control, with the lfo cross-fading between sine and
cosine for the left and right. Essentially at certain points throughout the
sweep of the rate control the lfos for Del2 left and right will either be in
sync or 90 degrees out of phase. This modulated output is then scaled
by the feedback control and fed back to the input of Del2.
 

Attachments

  • Halo Block Diagram.pdf
    22 KB · Views: 394
Yes, just assign the mix control modifiers to the same expression pedal.
Hi everybody, I’m relatively new in the fractal world. It has been very entertaining to follow this thread.

I just tried to assign the mix control modifiers of both delays to expression pedal, but there’s a notable difference in volume. I guess there’s a way to maintain the volume with the preset wet or dry. Sorry if my question is so easy to figure it out, it’s not that simple for me yet.

Thanks in advice
 
Hi everybody, I’m relatively new in the fractal world. It has been very entertaining to follow this thread.

I just tried to assign the mix control modifiers of both delays to expression pedal, but there’s a notable difference in volume. I guess there’s a way to maintain the volume with the preset wet or dry. Sorry if my question is so easy to figure it out, it’s not that simple for me yet.

Thanks in advice
If it's the latest version where they are in parallel, you want to control the Level parameter (so that dry level remains constant).
 
Howdy Folks!
I have read through...
Enjoy!
rk
Welcome, Robert! What a treat it is to be able to count you amongst our fraternity. Thank you so much for your incredibly generous contribution here. I think I can speak for everyone and say that we'll all look forward to seeing you around here more often. Cheers!
I blame @Burgs. He’s responsible for most of my GAS these days. 😂 Welcome @Robert Keeley! Loving my Germanium Super Phat Mod. Thank you for releasing a new batch!
Haha! Don't blame me! Just the messenger... The message is always great coming from Robert's camp, though. Can't go wrong. 🤘🏻👊🏻
 
The filter block in the preset is doing the tilt EQ thingy. PEQ is not really necessary. I used the EQ in the delay blocks for the high passing. If you look at the manual for the Halo, the high pass is barely active, so that's why it's set so low.

Assuming a linear range (which would give the highest frequency cut off in the lower ranges of knob settings), and that the manual is correct, the Halo preset on the pedal would have a high pass of approx 12-13 Hz. Just barely making sure the sub bass isn't getting out of hand as the repeats go on. But TBH, the difference is quite negligible. So it might as well not be there for that preset.
Got it, makes sense. Thanks again for the explanation. In a typical delay block, I like to roll off a bit more low end from the repeats. In this case, would that cause the reverb-like effect to be lessened?

EDIT: Wow! Didn’t see that @Robert Keeley had commented when I made this post. Best discussion ever!
 
Last edited:
I added some wish list items for the delay block:


In the mean time, since @Robert Keeley was pretty generous in sharing the block diagram of the halo, I used the following approach in the Axe-Fx III (patch attached)

timmy_andons.png

The two drive blocks are probably an overkill here - but my cab block is set-up with some panning so I didn't want to lose that stereo image I had already coming in - they are set to tape saturation - you have to balance drive and level controls here to tame the "dry" signal coming into the delays.

The Filter block is set to low pass (not sure what the cutoff frequency is setup for in the default preset in the Halo pedal, but I just set it to 2K here). and it's output reverses the right channel - this simulates the phase reversal going into Del2 for both L and R in the halo block diagram.

I've disabled the Delay blocks LFOs (depth set to 0%) since we can't quite get the same LFO configuration using the delay block LFOs as what is described in the Halo block diagram. Instead I've used LFO 1, from the controllers section, where LFO1A = sine and LFO 1B = cosine (since Output B Phase is set to 90 deg).

Delay Blocks are set to Dual Delay type.
  • Del1 L is simulated by Delay Block 1 L
  • Del2 L is simulated by Delay Block 1 R.
  • Del1 R is simulated by Delay Block 2 L
  • Del2 R is simulated by Delay Block 2 R.
  • Delay Block 1 Time L is assigned a modifier source of LFO1B (cosine)
  • Delay Block 2 Time L is assigned a modifier source of LFO1A (sine)
  • Delay Block 1 Time R is assigned a modifier with source 1 = LFO1A (sin) and source 2 = LFO1B (cos), operation is set to "Src1 + Src2"
  • Delay Block 2 Time R is assigned a modifier with source 1 = LFO1B(cos) and source 2 = LFO1A(sin), operation is set to "Src1 + Src2"

  • Feedback L>R is set to -100%, this simulates the phase reversal of output of Del1 into Del2 in the Halo block diagram.
  • Feedback R>L is set to 0% as it doesn't cross feedback like that.
  • Feedback L-L and R-R is set to 100% so we can use Master feedback instead as the main feedback control.
  • Both delay lines are panned to the LEFT for Delay Block 1 and to the RIGHT for Delay Block 2.
Controls
Time
  • You'll have to modify both Time L and Time R modifiers manually (Parameter range section) and maintain the .75 ratio between them. using a <time>-9ms for Min and <time>+9ms for Max for Delay 1/2 Time L and <time>-15ms for Min and <time>+15ms for Max for Delay1/2 Time R.
Depth
  • In the modifier panel for Time L and R on both blocks, you can use the Scale parameter in the Mapping section to simulate the depth knob.
Rate
  • Change the Rate in the controllers section for LFO 1.
Saturate
  • Increase the Drive in the Drive 3/4 blocks - you'll have to balance the overall level by lowering the Level parameter
  • Decrease the Filter block lowpass cutoff (Frequency parameter) as you add more drive (lowest is 1KHz, highest 8750Hz)
HPF
  • Modify the low Cut frequency in both Delay blocks EQ section, from 20 to 300Hz.
Tone
  • Modify the High Cut frequency in both Delay blocks EQ section, from 1000 to 8750 Hz.
FDBK
  • Adjust the Master Feedback control in both Delay blocks.
LEVEL
  • Adjust the Level control in both Delay blocks
To simulate the cross-fading done For Del2 LFO, we can change Scale 1 and Scale 2 for the Time R modifier in both blocks. For example:

  • One extreme, Scale 1 set to 100%, Scale 2 = 0%
    • This simulates Del 2 LFO being 90 deg out of shift with Del 1 LFO.
  • Other extreme, Scale 1 set to 0%, Scale 2 = 100%
    • This simulates Del 2 LFO being in sync with Del 1 LFO
  • Then for anything in between, we can set Scale 1 and Scale 2 on both blocks to add up to 100%, for example, (50%, 50%) or (20%, 80%) or (80%,20%) - you get the idea.



 

Attachments

  • Timmy Andons.syx
    48.2 KB · Views: 61
Last edited:
Hi guys, some days ago I made a preset from scratch watching the video of Andy Timmons and TPS, for my AZ Prestige HSS. I copy the great work that guitarnerdswe an others did about Halo and want to share with you. I hope it's ok.

The preset was made for my Ibanez AZ HSS, so maybe you have to tweak a little bit. I put a Graphic EQ because my guitar doesn't have a treble bleed so, using the volume pot in 5 aprox, made my sound a little darker. I spend my time in the 2d scene, TBH. My initial idea was to emulate four stages of gain, just like Andy.

I hope you like it. I made a quickly record of the sound of the preset with my AZ.


Cheers!!
 

Attachments

  • SEPU AT AZ PRAYER 2.syx
    24.1 KB · Views: 44
Last edited:
I added some wish list items for the delay block:


In the mean time, since @Robert Keeley was pretty generous in sharing the block diagram of the halo, I used the following approach in the Axe-Fx III (patch attached)

View attachment 105139

The two drive blocks are probably an overkill here - but my cab block is set-up with some panning so I didn't want to lose that stereo image I had already coming in -they are set to tape saturation with just default parameters - you have to balance drive and level controls here to tame the "dry" signal coming into the delays.

Filter is set to low pass (not sure what the cutoff frequency is setup for in the default preset in the Halo pedal, but I just set it to 3K here). and it's output reverses the right channel - this simulates the phase reversal going into Del2 for both L and R in the halo block diagram.

Delay 1 (Used for Left)
  • Dual Delay type
  • Feedback L>R is set to -100%, this simulates the phase reversal of output of Del1 into Del2 in the halo block diagram.
  • Feedback R>L is set to 0% as it doesn't cross feedback like that.
  • Feedback L-L and R-R is set to 100% so we can use Master feedback instead as the main feedback control.
  • Both delay lines are panned to the left.
  • Since we can't quite get the same LFO configuration using the delay block LFOs as what is described in the block diagram (Cosine for Del1, Sine for Del2) I'm instead using a modifier directly in the Time L and Time R controls (Time L gets modified by LFO 1B and Time R by LFO 1A)
  • So if you need a different time, you'll have to adjust the modifier range here for the prescribed (+- 9ms on Time L and +-15ms o Time R) -
    • You can use the scale parameter in the mapping section of the modifier to simulate the "depth" control
  • Drive, compander are off. LFO1/LFO2 depth is 0 since we are using modifiers instead.
Delay 2 (Used for Right channel)
  • The same as Delay 1 except:
  • Both Delay lines are panned to the right
  • Time L is modified by LFO 1A (Sine), Time R is modified by LFO 1B(Cosine)
Controllers:
  • The reason we need to use modifiers, is we can select which LFO side to use (A/B). By setting Output B Phase to 90 degrees and Sine type, LFO 1B becomes a cosine.
  • We can modulate Output B Phase parameter as well to simulate what the halo block diagram describes - "with the lfo cross-fading between sine and cosine for the left and right."

That's just stellar @AlbertA, nice work.
Wish it didn't take so many blocks.
Maybe we'll get a factory block for something like this some day :)
 
Back
Top Bottom