Digital audio converter (audio DAC) is a digital audio encoding converted to analog audio sound (for example, music, etc.) devices. In any digital audio code conversion process into audio converter device external noise coupling together will be the audio band produced huge influence. Such as DAC power supply AC ripple and switching noise, etc., is the main reason for the decline in the quality of the audio frequency conversion. Therefore, the design of high performance digital analog audio system requires that the audio DAC and the power rail noise isolation. In this paper, an integrated solution with high efficiency and linear power supply with high efficiency and linear power supply can solve the problem and provide a higher quality of audio.
Most modern audio are stored in digital format, for example: pulse encoding modulation (PCM) and MP3. It can provide lossless data storage, high quality perfect copy, unlimited storage, high flexibility and compatibility with other digital systems. Need to use an audio DAC to convert these digital format to analog signals, thereby driving the speaker to produce audio sound (analog wave). The audio amplifier is amplified by the converted audio sound, and the speaker transmits it to the audience.
It is generally considered that the analog audio sound is the final output of the audio system. Its quality depends on the entire audio system, including the original digital encoding itself, audio DAC devices, audio power amplifier and speaker or headphone quality.
If we focus our attention on the audio DAC, the performance depends on the quality of the DAC itself and is influenced by other external factors. High performance audio DAC is sensitive to external noise. These external noises will enter the audio band during the conversion. This noise can be derived from the AC power supply ripple, radio frequency interference, switching noise, and even the noise of other circuit components of the audio system. In this paper, we will explore how to improve the noise performance of the audio converter by improving the noise performance of the DAC power supply voltage.
Audio performance specification
In order to quantify the noise performance of a sound system, we need to measure some of the specifications. Total harmonic distortion (THD) determination of the number of undesirable signals generated by the audio converter during playback of audio signals. Systems such as audio converter are non ideal and nonlinear devices with single or multiple inputs and outputs. They always have the original input signal distortion. This distortion is often added to the original input signal. Therefore, the total harmonic distortion represents the distortion of the original signal is an ideal parameter to measure the performance of all audio DAC.
However, the total harmonic distortion is not itself, and does not contain the DAC to produce the output signal of other non distortion related noise. Therefore, the combination of total harmonic distortion and noise can be built up to another measurement standard, that is, THD+N specification. THD+N accurately quantifies all noise independent of the input signal generated by the DAC. The noise comes from the thermal noise of the circuit components of the power supply AC ripple, radio frequency interference, switching noise, vibration and audio system.
People usually use THD+N to regulate the performance of the DAC devices, but the performance of the DAC in the frequency band is not discussed. You need to use a FFT analyzer to analyze the quality of all analog audio signals in the frequency band. This type of analyzer uses the time to change analog audio output signals and converts it into a spectrum by using the fast Fourier transform (FFT) technique. This measurement process shows the performance of an audio converter in its entire KHz 1~20 range, and clearly shows the performance of the noise and harmonic distortion.