• Signal Type: It can carry both uncompressed PCM audio (Pulse Code Modulation) and compressed audio formats (e.g., Dolby Digital,  DTS).
• Transmission: It uses a coaxial electrical connection (RCA connector) to transmit the signal, typically with a 75-ohm impedance.
• Distance: Typically up to 10 meters (using high-quality cable).
• Usage: Common for consumer-level devices, such as CD players, DVD players, sound cards, and AV receivers.
• Maximum Bit Depth and Sample Rate: Limited to 24-bit depth and 192 kHz sample rate for uncompressed PCM, although compressed audio formats (e.g., Dolby Digital) can support higher sample rates.

• Signal Type: Same as coaxial S/PDIF, can carry both uncompressed PCM and compressed audio formats.
• Transmission: Uses optical fiber for transmission, so the signal is carried by light.
• Distance: Typically longer distances than coaxial (up to 20-30 meters), but can be affected by quality and fiber type.
• Usage: Commonly used for devices where electrical isolation is preferred (e.g., home theater systems, AV receivers, PCs).
• Maximum Bit Depth and Sample Rate: Similar to coaxial, it supports 24-bit depth and 192 kHz sample rate for PCM.

• Signal Type: Uncompressed PCM audio only, typically transmitted as 16-bit, 24-bit, or 32-bit audio samples.
• Transmission: It uses parallel transmission over multiple wires:
• LRCLK (Word Clock): Indicates left or right channel.
• BCLK (Bit Clock): Synchronizes timing of bits.
• SDATA (Serial Data): Carries the actual audio sample data.
• MCLK (Master Clock): Used for synchronization, optional in some setups.
• Distance: Short-range transmission (typically within a device, such as between a DAC and a microprocessor or audio chip).
• Usage: Typically used for internal communication within audio devices like DACs, ADCs, and audio processors.
• Maximum Bit Depth and Sample Rate: High-definition PCM with a wide range of bit depths and sample rates, often much higher than S/PDIF. I2S can support a wide range of rates depending on the word length and sampling rate, with typical maximums around 192 kHz and 24 bits per sample (bit clock up to 12 MHz). High-end systems might support 768 kHz or higher sampling rates, with higher bit depths (up to 32 bits), leading to even higher bit clocks.

• Signal Type: Uncompressed PCM audio and can also carry compressed audio.
• Transmission: Uses the USB (Universal Serial Bus) standard to transfer audio data between a host (e.g., PC, smartphone) and a peripheral device (e.g., DAC, audio interface).
• Distance: Can transmit over long distances (up to 5 meters or more with standard USB, but the range can be extended with USB hubs or repeaters).
• Usage: Common for PCs, DACs, external audio interfaces, and smartphones.
• Maximum Bit Depth and Sample Rate: Supports high sample rates (up to 384 kHz) and high bit depths (up to 32-bit or even floating point audio). USB 2.0 supports up to 24-bit/192kHz, while USB 3.0 and later can handle higher resolutions.
• Power Supply: USB can also provide power to devices (e.g., for portable DACs).

• Signal Type: Primarily uncompressed PCM audio. Can support multichannel audio (stereo or multi-channel, up to 8 channels).
• Transmission: Uses balanced electrical signals over XLR connectors (similar to microphone connections, with a 110-ohm impedance).
• Distance: Longer transmission distances than S/PDIF, up to 100 meters or more depending on the cable quality and signal strength.
• Usage: Typically used in professional audio equipment (e.g., mixing consoles, studio equipment, broadcasting systems).
• Maximum Bit Depth and Sample Rate: Supports 24-bit and 48 kHz by default, but higher sample rates (e.g., 96 kHz, 192 kHz) and bit depths (32-bit) are possible depending on equipment.

• S/PDIF (both coaxial and TOSLINK) is typically used in consumer-grade devices and supports compressed and uncompressed audio, with relatively limited distance capabilities (up to 10-30 meters).
• I2S is used internally within devices to transmit uncompressed PCM audio over short distances with high precision.
• USB Audio is used for external device connections, supports high sample rates and bit depths, and provides power to connected devices.
• AES/EBU (AES3) is a professional standard used for longer-distance transmission, commonly in studio and broadcasting environments, and supports multichannel audio
  

• A key difference between S/PDIF and AES/EBU, compared to I2S and USB Audio, is that the clock signal is separate in I2S and USB Audio. S/PDIF and AES/EBU use embedded clocks, making the transmission simpler but less precise. I2S and USB Audio use separate clocks, providing better timing accuracy and lower jitter, which is crucial for high-fidelity audio applications.

1. S/PDIF (Coaxial, TOSLINK)

Signal Type:

• S/PDIF (Sony/Philips Digital Interface) is a digital audio transmission standard used for both PCM (Pulse Code Modulation) and compressed audio formats (like Dolby Digital, DTS).

Signal Details:

• Coaxial S/PDIF:

  • The signal is transmitted as a low-voltage electrical signal over a coaxial cable (typically using an RCA connector).
  • Signal Level: The signal is typically transmitted at 0.5V (peak-to-peak), which represents the digital audio data.
  • Data Encoding:
    • PCM data is encoded in a series of voltage changes (a stream of 1s and 0s).
    • The data rate is generally 1-2 Mbps for stereo (two channels).
    • In compressed formats (e.g., Dolby Digital), the audio is compressed and transmitted at a higher rate, but the format is still a series of digital bits.
  • The signal is sent as two channels of data (stereo), with the left and right channels interleaved into the stream.

• TOSLINK S/PDIF:

  • Signal Transmission: Instead of an electrical signal, optical fiber carries the light pulses that represent the same binary data.
  • Light Encoding: The data is encoded into pulses of light. A digital light pulse represents a "1", and no pulse represents a "0".
  • Signal Level: The signal is transmitted as light at very low power, which can result in higher resistance to noise over longer distances compared to coaxial cables.
  • The data rate and encoding are the same as coaxial S/PDIF, and it uses the same PCM or compressed data formats.
  • The output from the TOSLINK receiver is typically a TTL signal (Transistor-Transistor Logic), which uses a low (0V) and high (e.g., 3.3V or 5V) voltage level. This signal may be in the form of voltage pulses, similar to SPDIF coax signals, but with differences in the physical transmission (optical vs coaxial cable).
  • TOSLINK output (TTL) signal is inverted, with low voltage (0V) for logic 1 and high voltage (3.3V or 5V) for logic 0.The term "inversion" more accurately refers to the timing of the signal edges or how the signal encoding is handled.There may be cases where the rising/falling edge used for encoding data differs between the two formats, making the signals appear inverted when decoded. However, the basic logic levels (0V and higher voltage) remain the same.

2. I2S (Inter-IC Sound)

Signal Type:

• I2S is a parallel digital audio signal used for interfacing between ICs (e.g., between a DSP and DAC).

Signal Details:

• Signal Transmission: I2S uses multiple parallel signal lines to transfer audio data synchronously between devices.
  • Typically uses 3-4 signal lines: Serial Clock (SCK), Word Select (WS), Serial Data (SD), and optionally Master Clock (MCLK).
  • Clock Signals:
  • SCK (Serial Clock): Synchronizes the data transmission. The clock drives the data bits on the data line.
  • WS (Word Select): Indicates whether the data being transferred is for the left or right audio channel.
  • SD (Serial Data): The actual audio data (PCM or sometimes DSD).
  • MCLK: Some systems use a Master Clock for synchronization, although many setups do not need it.
• Signal Level:
  • I2S typically uses logic-level voltage (either 3.3V or 5V depending on the system).
  • The data is transferred serially in frames, where each frame represents a single audio sample, typically for a stereo pair (left and right channels).
  • The signal is transmitted in audio word frames, where the Word Select signal determines which audio channel the data belongs to.
  • Data Rate: I2S can support very high sample rates, up to 32 bits and 384 kHz or higher, depending on the system. It is not limited by the consumer-focused formats of S/PDIF.

3. USB Audio

Signal Type:

• USB Audio is a serial digital signal transmitted via the USB protocol, commonly used for external audio devices like USB DACs and audio interfaces.

Signal Details:

• Signal Transmission: The digital audio data is transmitted over the USB data lines (usually D+ and D-).
  • The USB protocol transmits data in packets, which are structured for audio streaming. Audio data is divided into packets that are sent between the host (computer) and the audio device (USB DAC).
  • Signal Level: USB operates on logic-level voltages (typically 3.3V or 5V), where the D+ and D- lines carry the differential signal for data transfer.
  • The USB protocol is designed to support bidirectional data transfer (not just one-way as in S/PDIF), meaning it can handle both audio output and input in different directions.
  • Data Rate:
  • USB 2.0 can handle up to 24-bit/192 kHz audio.
  • USB 3.0 and higher can support 32-bit/768 kHz or DSD (Direct Stream Digital), enabling high-resolution audio streaming.
• Audio Formats: USB Audio can carry both PCM and compressed audio formats, and it can even handle DSD (Direct Stream Digital) if the DAC supports it.

4. AES/EBU (AES3)

Signal Type:

• AES/EBU is a professional digital audio signal standard, typically used for balanced transmission of audio signals over XLR (or sometimes BNC) connectors.

Signal Details:

• Signal Transmission: AES/EBU transmits digital audio data using a balanced differential signal. This makes it more robust to external noise and allows for longer cable runs compared to S/PDIF.
  • Signal Level: AES/EBU uses a 2V differential signal (balanced signal) over XLR connectors (or BNC connectors for coaxial connections).
  • The differential nature of AES/EBU signals allows the signal to be more immune to electrical noise and to travel longer distances (up to 100 meters with proper cables).
  • Data Encoding: AES/EBU carries PCM data, much like S/PDIF, but is designed to meet the requirements of professional audio applications.
  • Word Clock: AES/EBU systems often use a separate word clock (like AES11) to synchronize all devices in a system, which improves timing accuracy for multi-device setups.
  • Data Rate: Like S/PDIF, AES/EBU supports 24-bit/192 kHz audio but can support multi-channel (e.g., 8 channels) with the right setup.
  • Channel Support: Unlike S/PDIF, AES/EBU is often used for multi-channel audio, enabling professional audio systems (e.g., 8 channels over one cable).

Key Differences in Signal Details:

• Number of Wires: 2 wires
• Signal wire (carrying the digital audio data)
• Ground wire (for shielding and reference ground)
• Connector:
• RCA connector (for coaxial S/PDIF)
• The signal is transmitted through a coaxial cable, usually with a 75-ohm impedance.
• Cable: Coaxial cable with a single conductor, surrounded by insulation and an outer shield (used for grounding).
• Signal Type: Unbalanced electrical signal (single-ended).

• Number of Wires: 1 optical fiber (no electrical wires)
• The signal is transmitted as light pulses through the fiber.
• Connector:
• TOSLINK connector (optical fiber connector) for transmitting the digital signal. 

  Toslink connector typically has 3 pins. These pins are used for electrical connections that interface with the optical transceiver module.

  Here’s a breakdown of the pins:

• Vcc: Power supply (commonly 3.3V or 5V, depending on the TOSLINK module). Vcc powers the LED (light-emitting diode) inside the TOSLINK transmitter.
• GND: Ground connection.
• Signal (DATA): The input pin where the electrical digital signal (S/PDIF signal) is fed to the optical transmitter.
• Cable: Optical fiber cable (glass or plastic), used for light transmission. It’s immune to electrical noise interference but has distance limitations compared to coaxial cables.
• Signal Type: Optical signal (light pulses).

• Number of Wires: 4 or 5 wires (depending on configuration)

1. Serial Clock (SCK): Provides the clock signal for synchronization.
2. Word Select (WS): Selects the left or right channel (frame synchronization).
3. Serial Data (SD): Carries the audio data (either left or right channel).
4. Master Clock (MCLK) (optional): Used for high-precision applications, required for some devices, especially those with higher sample rates.
5. Ground: Common ground wire for the entire connection.

• I2S does not use a standard connector but typically uses 2-4-pin headers or dedicated pins on chips or development boards (e.g., on microcontrollers, DACs, or audio processors).

• Cable: Usually a flat ribbon cable or individual wires, often used in internal connections or on boards.
• Signal Type: Unbalanced (although it can be made differential using additional drivers).

• Number of Wires: 4 or 5 wires (depending on the USB standard)

1. Vcc (Power): Provides power (typically 5V).
2. Ground: Common ground.
3. D+ (Data +): Carries data (USB high-speed signal).
4. D- (Data -): Carries data (USB differential signal).
5. Shield: Used for grounding the shield to prevent interference.

• USB Type-A, Type-B, Type-C connectors (for host-side or device-side connections).

• Cable: USB cable with 4 or 5 wires depending on the version (USB 2.0, USB 3.0, etc.). The data transfer is done over differential pairs (D+ and D-), with power and ground lines included.
• Signal Type: Differential signal (USB data lines use differential signaling for noise rejection).

• Number of Wires: 3 wires

1. Signal+: Carries the positive phase of the balanced signal.
2. Signal-: Carries the negative phase of the balanced signal.
3. Ground: Reference ground.

• S/PDIF uses unbalanced electrical signals (coaxial) or optical signals (TOSLINK).
• I2S is a serial interface for audio data, typically unbalanced but can be differential.
• USB Audio uses differential signaling for data transfer, designed for high-speed data and power delivery.
• AES/EBU uses balanced differential signaling, making it ideal for professional audio environments due to its noise immunity.

• Bit Depth: Typically supports up to 24 bits.
• Although S/PDIF is capable of carrying 24-bit data, it’s more commonly used for 16-bit audio in consumer-grade equipment.
• Sampling Rate:
• In Hi-Fi devices, S/PDIF (both coaxial and TOSLINK) can support up to 24-bit/192 kHz audio, but the most common configurations are:
• 16-bit/44.1 kHz or 16-bit/48 kHz for standard consumer audio (e.g., CDs, DVDs, and lower-end streaming).
• 24-bit/96 kHz or 24-bit/192 kHz for Hi-Fi systems that require higher resolution audio.
• Overview:
• Maximum Bit Depth: 24-bit.
• Maximum Sample Rate: 192 kHz (typically up to 48 kHz for consumer-grade equipment).
• 16-bit/48 kHz is typically the default configuration for consumer-level audio devices (such as CDs, DVDs, and some streaming services), as it is the S/PDIF standard supported by most consumer-grade equipment.
• 24-bit/96 kHz and 24-bit/192 kHz are used in high-resolution audio formats and Hi-Fi systems. Many Hi-Fi DACs and audio interfaces can handle 24-bit/192 kHz over S/PDIF, providing better dynamic range and higher sample rates for more detailed audio reproduction.
• TOSLINK (optical) has a lower bandwidth than coaxial connections and may not always support the highest bit depth and sample rate. For example, some optical connections are limited to 24-bit/96 kHz or 24-bit/192 kHz, depending on the quality of the optical transceiver.
• For Hi-Fi audio, 24-bit/192 kHz is commonly supported and preferred in higher-end systems, especially when playing high-resolution audio formats (like FLAC or DSD) or hi-res streaming.

• Bit Depth: I2S is very flexible, and can support up to 32-bit audio.
• In practice, many systems use 16-bit or 24-bit I2S, but the interface is capable of handling up to 32 bits per sample.
• Sampling Rate:
• I2S can handle high sampling rates, typically up to 192 kHz, but with some specialized implementations, it can support even higher rates, including 384 kHz or beyond, depending on the hardware and clocking systems involved.
• Overview:
• Maximum Bit Depth: 32-bit (or higher in some systems).
• Maximum Sample Rate: 384 kHz (or higher with specialized setups).

• Bit Depth:
• USB audio interfaces typically support up to  24-bit audio.
• Some higher-end USB audio devices can support 32-bit float (or integer) formats for greater dynamic range, although this is not common in consumer-level equipment.
• Sampling Rate:
• The maximum sample rate depends on the USB version and the capabilities of the device:
• USB 2.0 supports up to 192 kHz.
• USB 3.0 and newer can theoretically support up to 768 kHz or even higher, with proper support from the interface and DAC.
• Overview:
• Maximum Bit Depth: 32-bit (with some devices supporting 32-bit float).
• Maximum Sample Rate: 768 kHz (depending on device and USB version).

• Bit Depth: AES/EBU supports up to 24 bits in most implementations.
• Some specialized professional equipment can handle 32-bit audio, but 24-bit is the most commonly supported bit depth in AES/EBU systems.
• Sampling Rate:
• AES/EBU is capable of supporting up to 192 kHz under normal conditions.
• However, specialized implementations can support rates up to 384 kHz or higher.
• Overview:
• Maximum Bit Depth: 24-bit (some support for 32-bit).
• Maximum Sample Rate: 192 kHz (384 kHz in some systems).

• S/PDIF (Coaxial and TOSLINK) is typically limited to 24-bit and 192 kHz.
• I2S offers greater flexibility, supporting up to 32-bit and 384 kHz (or even higher in some systems).
• USB Audio supports up to 32-bit (with 32-bit float possible) and 768 kHz (or more, depending on USB version and device).
• AES/EBU supports 24-bit audio and can handle up to 192 kHz, with some systems supporting higher rates.