Why Class D amplifiers sound rough, especially high. This is a very common problem,
       Class D power amplifiers convert analog signals into digital pulses via PWM (pulse width modulation), then amplify these pulses, and finally return to analog signals through a low-pass filter to drive the speaker. This design is efficient, small in size, low in heat, but there may be compromises in sound quality.
       The treble is rough, which may involve distortion or noise in the high-frequency part. I need to consider several possible reasons. The first is the question of switching frequency. The switching frequency of Class D power amplifiers is usually a few hundred kHz, and if the switching frequency is not high enough, the restoration of high-frequency signals may not be accurate enough, resulting in distortion. For example, when the switching frequency is close to or below 20kHz (the upper limit of human ear hearing), the high frequency part may be interfered with and produce a burr sensation.
     Then there's the feedback mechanism. Traditional Class D amplifiers may adopt an open-loop design and lack real-time feedback to correct distortion, especially in high frequency bands, where the signal changes quickly and it is easy to accumulate errors. Class AB amplifiers usually have a better feedback system, which can be adjusted in time to reduce distortion.
    Power supply noise is also a factor. Although the Class D power amplifier has high efficiency, it requires high purity of the power supply. If the power supply is not well designed, high-frequency switching noise may be coupled into the audio signal, especially in the treble part, because the high frequency is more susceptible to interference.
    The design of low-pass filters can not be ignored. If the performance of the low-pass filter after the class D output is insufficient, the residual high-frequency switching noise will be superimposed on the audio signal, resulting in high pitch rough. Good filter design can effectively filter out these noises, but cost or design limitations may result in poor filter performance.
    Possible causes include nonlinear distortion of components, such as the nonlinear characteristics of MOSFET switching, or improper PCB layout, resulting in signal interference. In addition, EMI interference, if not handled properly, can also affect the sound quality, especially the treble parts.
To optimize the design of the power source and filter, or consider other types of power amplifier. What users may not say is that they may want to improve sound quality without changing their device, or have concerns when choosing a device and need to weigh efficiency and sound quality.

Class D power amplifier (digital power amplifier) may have the problem of treble roughness in sound quality, mainly related to its working principle and design characteristics. The following is the specific reasons and technical analysis:

1. Interference of high-frequency switching noise
     Switching frequency limitation: Class D power amplifiers convert the audio signal into a pulse width modulation (PWM) signal via a high frequency switch (typically hundreds of kHz). If the switching frequency is low (such as close to or below 300kHz), the reduction accuracy of high frequency audio signals (such as above 20kHz) will decrease, resulting in distortion and noise.
    Residual noise leakage: If the low-pass filter at the output is insufficient, it cannot completely filter out high-frequency switching noise (such as PWM carrier residue), which will superimpose on the audio signal, making the high-pitched sound coarse.
 2. Nonlinear distortion switching device nonlinearity: The class D power amplifier MOSFET switch has nonlinear characteristics (such as dead time, on-resistance changes) when on/off, resulting in transient distortion of high-frequency signals.
    Modulation error: During PWM modulation, if the clock accuracy is insufficient or the feedback loop delay is large, the dynamic response of the high-frequency signal will deteriorate, resulting in harmonic distortion.
3. Power supply design defects
     Power noise sensitivity: Class D amplifiers have high efficiency, but are sensitive to power ripple. If the power supply filter is insufficient, the high-frequency switching noise will be coupled to the audio signal through the power line, especially affecting the treble purity.
       Dynamic current requirements: High frequency signals require a fast current response, and if the transient response of the power supply is insufficient (such as small capacitance and high ESR), it can lead to high-pitch dynamic compression or distortion.
 4. Insufficient feedback loop open loop design problem: some low-cost Class D power amplifiers use open loop design (no real-time feedback), which can not correct high-frequency distortion. The Class D power amplifier with closed-loop design suppresses distortion through feedback, and the sound quality is closer to Class AB.
     Loop delay: High-frequency signals change quickly, if the feedback loop delay is high (such as >1μs), the error cannot be corrected in time, resulting in loss of treble details
5. EMI and layout issues
      Electromagnetic interference (EMI) : The switching signal of Class D power amplifier is easy to produce electromagnetic radiation, if the PCB layout is unreasonable (such as poor ground design, improper location of filter components), it will introduce high-frequency interference, affecting the sound quality.
      Thermal noise and parasitic parameters: Parasitic inductors and capacitors in high frequency circuits may cause ringing effects, exacerbating the high pitch roughness.

solution
     1. Select a high-performance Class D amplifier: a closed-loop design with a high switching frequency (such as >500kHz) is preferred (such as TI TPA3255, Infineon MA12070).
     2. Optimize power supply design: Use low ESR capacitors, LC filter circuits, or separate regulated power supplies to reduce high-frequency noise.
     3. Enhanced filtering: Use a high-order low-pass filter (such as order 3 or 4) at the output end, and select a low-loss core inductor.
     4. Suppress EMI: reasonable layout of PCB, shorten high-frequency path, increase shielding and magnetic bead filtering.
     5. With high-quality speakers: the treble unit has high sensitivity and needs to be matched with low-distortion speakers to avoid exposing the weakness of the power amplifier.
     The treble scratchy problem of Class D power amplifier is mainly due to switching noise, nonlinear distortion and power supply design, but by optimizing the circuit, selecting high-performance chips and rationally matching the system, the sound quality close to Class AB power amplifier can be achieved. Modern high-end Class D amplifiers (such as the Purifi, Hypex NCore series) have significantly improved high frequency performance, demonstrating the potential of technological advances.

To put it simply, the high frequency roughness of Class D amplifiers is mainly:
    1, to have a high PWM frequency;
    2, to have a good filter and filter design;
    3, to have a good clean switching power supply