.. include:: ../../links.inc Audio stimulation ================= 2 separate audio stimulation systems are available. Each system has a different frequency and latency response. .. grid:: .. grid-item-card:: Natus TIP-300 :link: natus.html :link-type: url :text-align: center .. image:: ../../_static/devices/natus-tip-300.png .. grid-item-card:: SoundPixx :link: soundpixx.html :link-type: url :text-align: center .. image:: ../../_static/devices/soundpixx-light.png :class: only-light .. image:: ../../_static/devices/soundpixx-dark.png :class: only-dark Both audio stimulation systems are connected to a USB audio interface `Crimson 3`_ from `SPL`_. .. figure:: ../../_static/devices/crimson.png :width: 700 :align: center The configuration is detailed on labels on the `Crimson 3`_. Select Natus TIP-300 or SoundPixx --------------------------------- The button ``Speakers: A to B`` selects the system in use. If the button is ``OFF``, the speakers ``A`` corresponding to the :ref:`devices/audio/natus:Natus TIP-300` system is selected. If the button is ``ON``, the speakers ``B`` corresponding to the :ref:`devices/audio/soundpixx:SoundPixx` system is selected. .. tip:: If the :ref:`devices/audio/soundpixx:SoundPixx` is in-use, don't forget to turn on the SoundPixx controller. Microphone inputs 1/2 --------------------- The 2 microphone inputs 1 and 2 must be used without 48V phantom power and without high-pass filter. The microphone 2 is connected to the black microphone used to speak to the participant through the in-ear headphones. To enable the black microphone, both the ``Inputs: 1|2`` and ``Inputs: Mono`` button must be enabled. .. tip:: The black microphone has a low volume. Don't forget to turn the knob of input 2 to a high value. However, don't set it to max as it would leave a background noise. The LEDs ``SIG`` of the microphone input 2 should remain off while the black microphone is not in use. Audio sources ------------- Auditory stimulation can come from 2 sources: the `Chronos`_ if `E-Prime`_ is used or directly the computer sound (DAW). Only one of the 2 sources should be active at a time. To use the sound from the `Chronos`_, the button ``Sources: RCA`` must be enabled. To use the sound from the computer, the button ``DAW: 1|2`` must be enabled. .. note:: On Windows, the computer sends sound to a single channel, ``DAW: 1|2``. However on Linux, it sends sound to both channels, ``DAW: 1|2`` and ``DAW: 3|4``, thus enabling both yields a higher volume. Monitoring feedback ------------------- The sound from the audio stimulation system is redirected on an MEG analogical channel, ``MISC 006``, from the ``Phones 1`` output. See the section :ref:`trigger to sound onset delay ` and the tutorial :ref:`tut-proxy-audio-measure` for additional information. 2 Bose speakers are used to monitor the sound played through the audio stimulation system. The Bose speakers are connected on ``Phones 2`` and volume is adjusted both with a knob on the speakers and with the knob ``Phones 2`` on the `Crimson 3`_. Main volume ----------- The main volume knob affects the volume from all sources. The volume should be gradually increased from a low value up-to the desired value to prevent loud sound from deafening participants. Trigger to sound onset delay ---------------------------- The delay between the trigger and the sound onset is the delay between the trigger delivered to the :ref:`MEG trigger system ` and the actual sound onset in the earphones. This delay is composed of: - (1) The hardware delay from the `Crimson 3`_ soundcard to the audio delivery system, :ref:`devices/audio/natus:Natus TIP-300` or :ref:`devices/audio/soundpixx:SoundPixx`. - (2) The software delay due to the stimulation software (e.g. `E-Prime`_, `PsychoPy`_, etc..) and to the audio drivers and communication with the `Crimson 3`_ soundcard. .. image:: ../../_static/devices/audio-system-light.svg :align: center :class: only-light :width: 600 .. image:: ../../_static/devices/audio-system-dark.svg :align: center :class: only-dark :width: 600 Hardware delay ~~~~~~~~~~~~~~ The delay (1) from the `Crimson 3`_ soundcard to the audio delivery system is constant and depends only on the system in use. The :ref:`optimic ` can be used to record the sound output from the headset and to compare it with the sound output from the monitoring feedback ``Phones 1``, available on ``MISC 006``. +--------+-----------------------------+-------------------------+ | | .. centered:: Natus TIP-300 | .. centered:: SoundPixx | +--------+-----------------------------+-------------------------+ | Delay | .. centered:: 3 ± 0 ms | .. centered:: 18 ± 0 ms | +--------+-----------------------------+-------------------------+ The difference between both system comes partially from the amplifier/transducer, but mostly from the :ref:`devices/audio/soundpixx:SoundPixx` tube length of 3.6576 meters (12 feet) inducing a 10.6 ms delay due to the sound travel time. .. note:: The measurement through the :ref:`optimic ` is difficult even with sound output from the headset maximize. To improve it, shielding from environmental noise is necessary. Moreover, the :ref:`optimic ` is adding a source of unmeasurable delay, the delay of the measure. This delay is assumed to be constant and sub-millisecond. Software delay ~~~~~~~~~~~~~~ The software delay depends on the audio drivers and operating system as well as the audio stimulation software used and the code associated with it. This delay should be measured for every project paradigm. This delay is unlikely to vary in time, i.e. the same program delivering auditory stimuli on the same hardware should have the same delay across different sessions. See the tutorial :ref:`tut-precise-audio` for a Python example using `PsychoPy`_. To measure the delay, replace the sound with a pure tone and record the triggers and the sound on the ``MISC 006`` channel through the ``Phones 1`` monitoring feedback. This testing setup works best with a pure tone sound at 1 kHz, downloadable below: .. image:: ../../_static/icons/audio-file.svg :align: center :alt: Download sound file :target: ../../_static/downloads/sound/tone_1000Hz.wav :width: 100 Do not forget to increase the sampling rate of the MEG to at least 2 kHz to correctly sample the 1 kHz pure tone sound.