The EarStudio is a versatile audio device designed to enhance your listening experience through various connectivity options and customizable features. It serves as a portable DAC (Digital-to-Analog Converter) and headphone amplifier, offering high-quality audio streaming and playback control.

Function Description

The EarStudio primarily functions as a high-fidelity audio device that connects wirelessly via Bluetooth or wired via USB to your smartphone, computer, or other audio sources. It processes digital audio signals and converts them into analog sound for your headphones, aiming to deliver superior sound quality compared to direct connections. The device also supports hands-free calling with integrated microphone controls.

Usage Features

Power On/Off: To power on the EarStudio, press and hold the power button for more than 2 seconds. A blue LED will blink once, and a "power-on sound" will play. The device will automatically attempt to connect to a previously paired device, indicated by a green LED blinking once every 3 seconds. If no device is found, it enters Discoverable/Pairing Mode, with the green LED blinking twice every 0.5 seconds. To power off, press and hold the power button for more than 4 seconds. A red LED will blink once, and a "power-off sound" will play before the device shuts down.

Playback Control: For play/pause functionality, simply press the power button once. During Bluetooth or USB playback, a green LED will slowly blink once every 3 seconds.

Hands-free Calling: When an incoming call is received, the blue LED will slowly blink once every 3 seconds, accompanied by a "call-receiving sound." Press the power button once to answer the call. To reject an incoming call, press and hold the power button for more than 2 seconds; a "call-rejection sound" will confirm the action. To end an active call, press the power button once, and a "call-end sound" will play.

Track Navigation: The device features dedicated buttons for track control. Press the "Next Track" button once to skip to the next song. Press the "Previous Track" button once to go back to the previous track.

Pairing Mode: To manually enter Discoverable/Pairing Mode, press and hold the "Previous Track" button for more than 2 seconds. The green LED will blink twice every 0.5 seconds after an "enter pairing-mode sound," and the device will disconnect from any currently connected device.

Volume Control: The EarStudio has separate volume up and down buttons. Pressing the "Volume Up" button once increases the volume by 0.5dB. Pressing it multiple times or holding it down will consistently increase the volume up to 6dB. Similarly, pressing the "Volume Down" button once decreases the volume by 0.5dB. Holding it down will consistently decrease the volume down to -60dB. Pressing the "Volume Down" button at the minimum volume level will mute the sound.

LED Indicators: The device uses LED lights to indicate its status:

Discoverable/Pairing Mode: Green LED blinks twice every 0.5 seconds.
Bluetooth Connected: Green LED blinks once every 3 seconds.
Incoming/Outgoing Call: Blue LED blinks 3 times every 2 seconds.
Active Call: Blue LED slowly blinks once every 3 seconds.
Bluetooth/USB Playback: Green LED slowly blinks once every 3 seconds.
Battery Low: Red LED maintains the regular pattern, but the LED-off phase changes to red.
Charging: Red LED maintains the regular pattern, but the LED-off phase changes to red.
Charging Complete: Green LED maintains the regular pattern, but the LED-off phase changes to green.

App Connection and Features: The EarStudio can be controlled via a dedicated smartphone app. To connect, turn on the EarStudio, and it will automatically enter pairing mode. Select "EarStudio" from your smartphone's Bluetooth settings. Once connected, the app provides extensive control over the device's settings.

Tone Volume: Within the app, you can adjust the volume of local playback sounds such as power on/off, pairing, connected, and low-battery alarms. A "Test Tone Play" button allows you to hear the currently set tone volume.

LED Option: The app allows customization of the LED color. Options include Red/Green/Blue (default, based on device status), White (white LED only for all statuses), or Off (LED off in all statuses).

Bluetooth Option: This setting allows you to manage Bluetooth performance.

Buffer Length: Shorter buffer lengths can reduce latency but may cause audio lag in poor RF environments. A buffer length of 7 or higher is recommended for seamless audio streaming. This option is only available when Bluetooth audio streaming is not active.
Codec Option: Provides a way to limit the choice of codecs for the transmitter and allows users to prefer specific codecs. The active codec selection ultimately depends on the smartphone's policy.
HD Jitter Cleaner: Enhances phase accuracy by removing jitter caused by clock mismatches between source and sink devices. Settings can be applied separately for Bluetooth and USB playback.

USB Connection Option: This feature allows you to configure how the EarStudio interacts when connected via USB.

Battery Care: This feature helps maximize battery life by charging the battery only up to 80-90%, depending on conditions.

Charger Mode:

Normal Mode: The ES100 resets automatically when connected/disconnected to a USB charger or Host PC.
Auto Power Off when Charger Connected: The ES100 turns off when connected to a USB charger but stays on as a USB DAC when connected to a Host PC.
Auto Power Off when Charger Disconnected: The ES100 turns off when disconnected from a USB charger or Host PC. This mode is useful for car aux-in applications, where the ES100 turns on and off with the vehicle's USB power source.

Power Mode: The USB Power Mode can be set to Self-Powered Mode, useful when a USB Host requires it (e.g., connecting to an iPhone with an Apple Camera Kit). In this mode, the EarStudio will not charge. If the battery is low, Self-Powered mode is automatically released when the USB cable is connected.

Output Mode: This setting configures the audio output. The EarStudio supports 3.5mm and 2.5mm output modes. The 2.5mm port is a full-differential balanced output.

Analog Volume: The app provides a slider to control the analog volume. This volume can be set separately for calls and music playback. Audio volume during a call can only be controlled while a call is active.

Device Volume Control: This feature allows control over the device's internal volume.

Channel Trim Volume: Allows adjustment of the left/right channel trim volume.

Output Level Estimation: The app can monitor the ES100's output voltage in dBu and dBV formats. When used as a headphone amplifier, it can estimate the sound pressure level (dB SPL). For precise estimation, the source volume should be at maximum.

Source Volume: When USB streaming, this displays the USB Host's volume. Otherwise, it shows the smartphone's volume. USB Source Volume cannot be controlled via the app. Keeping the source volume at maximum is recommended for optimal audio performance.

Microphone Volume (during a call): Allows control of the microphone volume during a call. When on a call with EarStudio, the Source Volume automatically switches to control Microphone Volume. Enabling "Preamp" increases the volume by 21dB.

Microphone Loopback (during a call): Controls the amount of sound from the microphone that is directly fed to the audio output during a voice call.

Equalizer Tab: The equalizer offers 12 basic presets (e.g., Flat, Classical, Jazz, Pop, Rock, Dance, R&B, Hip-Hop, Bass Booster, Bass Reducer, Treble Booster, Treble Reducer) and 4 user-definable presets. Users can adjust sliders to desired values and save them to a user preset by pressing the preset button for 3 seconds or more. Preset names can be customized.

Sound Control Tab:

DCT (Digital Clarity Technology): Eliminates subtle digital noise and restores sound details. Higher levels increase DCT intensity.
Crossfeed: Simulates a loudspeaker listening environment by mixing left and right channels based on Head-Related Transfer Functions (HRTFs).
DAC Digital Filter: Allows selection of digital filter settings for the built-in AK4375a DAC. Options include Sharp Roll-Off (powerful sound with pre and post echoes), Slow Roll-Off (minimal echo, original sound), Short Delay Sharp Roll-Off (post echo enhances bass), and Short Delay Slow Roll-Off (minimal echo, original sound).
DAC Over Sample Rate: Allows setting the oversampling rate for the AK4375a DAC (1x, 2x, 4x).

Ambient Sound Tab:

Ambient Sound: In Ambient mode, the DSP mixes streamed music with ambient sound captured by the built-in microphone. Options include "Music Only" (0% ambient sound), "50%" (50% music, 50% ambient sound), and "Ambient Only" (0% music, 100% ambient sound). This feature is useful for situational awareness, such as cycling or hearing announcements.
Ambient Sound Microphone Volume: Adjusts the volume of ambient sound before it's mixed by the DSP. A higher volume captures louder ambient sound. Enabling "Preamp" increases the volume by 21dB. This is distinct from the microphone volume during a call.
Ambient Shortcut Key: Allows users to enable or disable the "Ambient Shortcut Key" functionality. When enabled, pressing and holding the "Next Track Button" toggles Ambient Mode on or off. This shortcut is only available during playback.

Maintenance Features

Factory Reset: To perform a factory reset, press and hold the "Volume Up," "Volume Down," "Previous Track," and "Next Track" buttons simultaneously. While holding these buttons, connect the EarStudio to a USB power source. Unlike a normal reset, the green LED will blink first. After the reset, disconnect and reconnect the EarStudio via USB; the blue LED will come on first, followed by the green LED blinking.

Device Firmware Upgrade (DFU): The EarStudio's firmware can be updated to incorporate new features and improvements. The latest firmware and a detailed "DFU user's guide" are available on the Radsone website.

USB Cable Check: Ensure your USB cable supports data communication. When connected to a PC in normal mode, "EarStudio USB DAC" should appear in the device list.
DFU Prepare: Download and unzip the latest firmware archive.
Entering DFU Mode: While pressing and holding the Power Button, connect the EarStudio to a PC via the USB data cable. The LED will turn off if DFU mode is successfully entered.
Running the Update: For Windows, execute "run_win32.bat" or "run_win64.bat." For macOS, install Homebrew, then libusb, and run "./run_macOS.sh" from the terminal in the DFU folder. Follow the on-screen prompts (press "Enter," then "y").
Completion: The EarStudio will reset automatically once the DFU is finished. Keep the device connected until you see the message "Firmware update completed / Device restarting."

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