Record and use spatial audio impulse responses in Ambisonics format

ZYLIA ZM-1 is a 3rd order Ambisonics microphone. That is excellent information if you want to capture and use 3D audio Impulse Responses (IR). In this case, you get a recorded 3rd order Ambisonics IR (3AIR).

​Below is a short introduction to the recording and using 3AIR with your podcast, film, or game production.​

​Recording of Ambisonics (spatial audio) Impulse Responses

What do you need?

• ZYLIA ZM-1
• A balloon

​The process:

1. Start recording in the ZYLIA Studio application or your favorite DAW.
2. Pop the balloon where you want to have a source. We did this about 1 meter in front of ZM-1.
3. Stop the recording and export the raw 19-channel file.
4. Convert 19 channels A-format to Ambisonics B-format (3AIR) with the ZYLIA Ambisonics Converter plugin.

​Zylia Ambisonics Reverb by multichannel convolution

The next step is a convolution of your 3AIR with your mono or multichannel signal to which you would like to add a reverberation effect.

Requirments:
​

• Example configuration files, sample IR and REAPER project
• MCFX plugins
• ZYLIA Ambisonics Converter plugin

n​The process:

1. Create folder named "mcfx" in C://Users/your-name/AppData/Roaming/ (~/Library/ on macOS).
2. Create folder named "convolver_presets" in C://Users/your-name/AppData/Roaming/mcfx (~/Library/mcfx on macOS).
3. Start recording in the ZYLIA Studio application.
4. Pop the balloon in a place where you want to have a source. We did this about 1 meter in front of ZM-1.
5. Stop the recording and export the raw 19-channel file.
6. Open the file in DAW (e.g., Audacity) and process the IR recording in the following way:

• Identify the reference channel - that is the one in which the IR main peak appears earlier than in other media,
• Trim all the channels in that way that the maximum amplitude value of the registered IR in the reference channel will be positioned precisely at the 100th sample. You can also shorten the recording by cutting out the samples for which the value of IR amplitude is close to 0,
• Once the recording is trimmed, read its length expressed in samples.

7. Go to the end of the project and read the length of one channel in the samples.
8. Export the file from DAW as 19 channel.
9. Open ZYLIA Ambisonics Converter and convert the 19 channel file to 3-rd order Ambisonics with SN3D normalization and ACN channel ordering.
10. Save the file to C://Users/your-name/AppData/Roaming/mcfx/convolver_presets (~/Library/mcfx/colvolver_presets on macOS)​.

In case you want to apply 3AIR to a mono file:

• Open the notepad application.
• Copy/Paste this text to notepad:

#               in out  gain  delay  offset  length  chan      file
# ---------------------------------------------------------------------
#
/impulse/read 1 1 0.1 0 0 IR_length 1 16_channel_IR.wav
 
/impulse/read 1 2 0.1 0 0 IR_length 2 16_channel_IR.wav
/impulse/read 1 3 0.1 0 0 IR_length 3 16_channel_IR.wav
/impulse/read 1 4 0.1 0 0 IR_length 4 16_channel_IR.wav
 
/impulse/read 1 5 0.1 0 0 IR_length 5 16_channel_IR.wav
/impulse/read 1 6 0.1 0 0 IR_length 6 16_channel_IR.wav
/impulse/read 1 7 0.1 0 0 IR_length 7 16_channel_IR.wav
/impulse/read 1 8 0.1 0 0 IR_length 8 16_channel_IR.wav
/impulse/read 1 9 0.1 0 0 IR_length 9 16_channel_IR.wav
 
/impulse/read 1 10 0.1 0 0 IR_length 10 16_channel_IR.wav
/impulse/read 1 11 0.1 0 0 IR_length 11 16_channel_IR.wav
/impulse/read 1 12 0.1 0 0 IR_length 12 16_channel_IR.wav
/impulse/read 1 13 0.1 0 0 IR_length 13 16_channel_IR.wav
/impulse/read 1 14 0.1 0 0 IR_length 14 16_channel_IR.wav
/impulse/read 1 15 0.1 0 0 IR_length 15 16_channel_IR.wav
/impulse/read 1 16 0.1 0 0 IR_length 16 16_channel_IR.wav
# -----------------------end of file -----------------------------------

• Replace "16_channel_IR" with your IR file name.
• Replace "IR_length" with the length of your IR in samples.
• Click on File/Save As...
• Change "Save as type:" to "All files (*.*).
• Change "File name:" to: "zylia-rir-mono-configuration.conf".
• Save the file to C://Users/your-name/AppData/Roaming/mcfx/colvolver_presets (~/Library/mcfx/colvolver_presets on macOS).
• Create a new session in REAPER.
• Insert your mono file.
• Add mcfx_convolver16 plugin.
• Click "open/open from file" and choose your configuration file ("zylia-rir-mono-configuration.conf").
• Add some Ambisonics to the Binaural converter (we recommend IEM plugin).

In case you want to apply IR to 19 channel file:​

• Open the notepad application.
• Copy/Paste this text to notepad:

#               in out  gain  delay  offset  length  chan      file
# ---------------------------------------------------------------------
#
/impulse/read 1 1 0.1 0 0 IR_length 1 16_channel_IR.wav
 
/impulse/read 2 2 0.1 0 0 IR_length 2 16_channel_IR.wav
/impulse/read 3 3 0.1 0 0 IR_length 3 16_channel_IR.wav
/impulse/read 4 4 0.1 0 0 IR_length 4 16_channel_IR.wav
 
/impulse/read 5 5 0.1 0 0 IR_length 5 16_channel_IR.wav
/impulse/read 6 6 0.1 0 0 IR_length 6 16_channel_IR.wav
/impulse/read 7 7 0.1 0 0 IR_length 7 16_channel_IR.wav
/impulse/read 8 8 0.1 0 0 IR_length 8 16_channel_IR.wav
/impulse/read 9 9 0.1 0 0 IR_length 9 16_channel_IR.wav
 
/impulse/read 10 10 0.1 0 0 IR_length 10 16_channel_IR.wav
/impulse/read 11 11 0.1 0 0 IR_length 11 16_channel_IR.wav
/impulse/read 12 12 0.1 0 0 IR_length 12 16_channel_IR.wav
/impulse/read 13 13 0.1 0 0 IR_length 13 16_channel_IR.wav
/impulse/read 14 14 0.1 0 0 IR_length 14 16_channel_IR.wav
/impulse/read 15 15 0.1 0 0 IR_length 15 16_channel_IR.wav
/impulse/read 16 16 0.1 0 0 IR_length 16 16_channel_IR.wav

# -----------------------end of file -----------------------------------

• Replace "16_channel_IR" to your IR file name.
• Replace "IR_length" with the length of your IR in samples.
• Click on File/Save As...
• Change "Save as type:" to "All files (*.*).
• Change "File name:" to: "zylia-rir-16-configuration.conf".
• Save the file to C://Users/your-name/AppData/Roaming/mcfx/colvolver_presets (~/Library/mcfx/colvolver_presets on macOS).
• Create a new session in REAPER.
• Insert your 19-channel file.
• Add ZYLIA Ambisonics Plugin
• Change configuration to 3-rd order, SN3D normalization, ACN ordering.
• Add mcfx_convolver16 plugin
• Click "open/open from file" and choose your configuration file ("zylia-rir-16-configuration.conf").
• Add Ambisonics to the Binaural converter (we recommend IEM plugin).

​The theory behind Ambisonics Impulse Response measurement

A more detailed description you can find in here:
​

• Room Impulse Responses as temporal and spatial filters
• Recording Impulse Responses

These articles go deeper into the technics of recording an impulse response. Raw Impulse Response recorded with ZM-1 can be converted to B-format (Ambisonics) and used to add reverbs in Ambisonics encoding.

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