Best practice to calibrate estim signal for webtease?

[picofarad]

Most estim webteases have a calibration function before you begin. Some are just straight up -- turn up signal until... Others, instruct you (while not connected) increase the computer signal until it registers on your device. Then to connect and calibrate using the estim device.

My setup is: from the computer I feed my amp (Fosi Audio BT20A Pro Bluetooth Stereo Amplifier) via Bluetooth. This gives me isolation and fewer cables. It then goes into a box I built that has two audio transformers and a pair of current reducing 4-ohm resistors. viewtopic.php?p=361126#p361126

I usually set the volume on the amp at 50% and then calibrate using the computer volume (the computer has a fairly high-end sound chip/card. I do this primarily since it is easier to get fine tuning from the computer rather than from the amp. Does this make sense or am I doing it wrong?

A further question deals with inserting a pair of volume controls viewtopic.php?p=380037#p380037 so I can balance the signals as part of the initial calibration. My question is: should I insert these volume controls after the transformers before the electrodes? Or would it be better to insert between the amp output and the transformer input?

Thanks!

[edger477]

Since you use Bluetooth amp, your sound card is not used. Bluetooth output is seen as audio card on computer.

You can't add volume controls after the amp. If amp has volume control, that is it, in case of amp with audio input, you add volume control there, on line input signal. For Bluetooth amp you use sndvol32 in windows.

[Majikthise]

As far as I know, there is no "right" answer to this. Every set-up is different, and different people seem to have different ideas about how to calibrate a set up like yours.

My thought would be to start with your sound card volume at about 50% and adjust it to ensure a clean, strong signal to the amp without over-driving it.

Then I would set the amp to about 50% and see how the volume controls on the box behave. My goal would be to ensure that it feels good and maybe a little strong with the volume knobs on the box at about 50%, and that you don't have huge swings in power when you adjust the controls on the box, but you can still turn it up a bit if you want to ramp during a session. You can adjust the amp so that the box reacts the way you want it to.

Again, everyone is different and ymmv. Good luck, and have fun!

[picofarad]

Since you use Bluetooth amp, your sound card is not used. Bluetooth output is seen as audio card on computer.

You can't add volume controls after the amp. If amp has volume control, that is it, in case of amp with audio input, you add volume control there, on line input signal. For Bluetooth amp you use sndvol32 in windows.

The sound card does not apply electrical amplification, but it does control the quality and strength (amplitude) of the signal being sent via blue tooth to the Fosi amp.

So, let's not call them volume controls but rather balance controls (both are variable resistors). I will try that windows control. It would be easier to control channel amplitude on the computer.
Thanks

[edger477]

The sound card does not apply electrical amplification, but it does control the quality and strength (amplitude) of the signal being sent via blue tooth to the Fosi amp.

When using a Bluetooth connection, the sound card's DAC and amplification functions are bypassed. The sound card can't affect the audio because the audio signal is being transmitted digitally and wirelessly via Bluetooth.

How Bluetooth Audio Works
For a sound card to affect the audio, a physical wired connection is required. When you use Bluetooth, the process is different:

• The digital audio file (e.g., MP3, FLAC) from your device is sent to the Bluetooth transmitter (the computer's Bluetooth chip).
• The Bluetooth transmitter compresses and converts this digital data into a radio signal.
• This radio signal is then sent wirelessly to the Bluetooth receiver in the Fosi amp.
• The Fosi amp's built-in digital-to-analog converter (DAC) then decodes the signal and converts it into an analog waveform.
• The amp then amplifies this analog signal to drive the speakers

The sound card's DAC and amplifier are not used in this chain. The only way a sound card would affect the sound is if you were to connect the computer to the Fosi amp using a physical cable, bypassing the Bluetooth connection entirely.

If you open sndvol you can see that in list of devices. Your sound card will be separate device, with its own volume control while each bluetooth device will appear as an entry and its volume is completely independent from other devices. Changing volume of sound card does not affect volume of bluetooth devices, and even sound card's outputs might be separate devices (like for me here Sound Blaster Z has independent stereo output and SPDIF-Out)

Screenshot 2025-08-30 212725.png (30.1 KiB) Viewed 11880 times

You can also control balance if you select your device (i.e. Fosi Bluetooth) then click on the icon above volume slider, and inside you have levels -> balance. I used to control L/R like that before I abandoned stereostim for foc-stim devices.

[picofarad]

@edger477
Thanks, for whatever reason I couldn't didn't find that app. I now can see how to adjust balance.
I obviously misunderstood the signal path when using Bluetooth.

[edger477]

Thanks, for whatever reason I couldn't didn't find that app

In windows open "run" (win key + r) and type "sndvol" (without quotes) and enter/ok

[picofarad]

Thanks, for whatever reason I couldn't didn't find that app

In windows open "run" (win key + r) and type "sndvol" (without quotes) and enter/ok

Found it, thanks!!

[edger477]

Ok, great thing about bluetooth is that if you don't use the amp for anything else, you can set up L/R balance for your electrodes you always use, and if you have another volume control on amp then you can leave this one (in sndvol) at 70-80% and do calibration using volume control on amp. The left/right balance should stay across sessions (check few times just in case), when you disconnect amp and later reconnect for new session. If you reconnect it before starting ScriptPlayer or Restim, they should start with the output device already selected as your amp.