1. SPL: sound pressure level
SPL是声压级的缩写，是响度的传统表达方法。其单位是dB SPL。设定20uPa对应于0dB SPL，这也基本是听域的下极限。声压随着与声源距离的增加而降低，5英尺距离正常的说话声平均大致为60dB SPL。 声压为1Pa时，相当于20log(1/0.000020)=94dB SPL 声压为1uPa即0.1Pa时，相当于74dB SPL 传声器灵敏度的参考声场压力为94dB SPL。在空气中参考声压p(ref）一般取为2*10E-5帕，这个数值是正常人耳对1千赫声音刚刚能觉察其存在的声压值，也就是1千赫声音的可听阈声压。一般讲，低于这一声压值，人耳就再也不能觉察出这个声音的存在了。显然该可听阈声压的声压级即为零分贝。
2. DRC: Dynamic range compression (DRC)
simply compression is an audio signal processing operation that reduces the volume of loud sounds or amplifies quiet sounds thus reducing or compressing an audio signal's dynamic range. Compression is commonly used in sound recording and reproduction, broadcasting,[1] live sound reinforcement and in some instrument amplifiers. Downward compression reduces loud sounds over a certain threshold while quiet sounds remain unaffected. A limiter is an extreme type of downward compression. Upward compression increases the loudness of sounds below a certain threshold while leaving louder sounds unaffected. Both downward and upward compression reduce the dynamic range of an audio signal.[2]
3. EQ: Equalization
equalisation is the process of adjusting the balance between frequency components within an electronic signal. The most well known use of equalization is in sound recording and reproduction but there are many other applications in electronics and telecommunications. The circuit or equipment used to achieve equalization is called an equalizer. These devices strengthen (boost) or weaken (cut) the energy of specific frequency bands or "frequency ranges". In the field of audio electronics, the term "equalization" (or "EQ") has come to include the adjustment of frequency responses for practical or aesthetic reasons, often resulting in a net response that is not truly equalized. The term EQ specifically refers to this variant of the term.[4] Stereos and basic guitar amplifiers typically have adjustable equalizers which boost or cut bass or treble frequencies.
4. Bass Enhancement
Small loudspeakers typically have a poor low frequency response, which can have a negative impact on overall sound quality. This example implements psychoacoustic bass enhancement to improve sound quality of audio played on small loudspeakers.
The example is based on the algorithm in [1]. A non-linear device shifts the low-frequency range of the signal to a high-frequency range through the generation of harmonics. The pitch of the original signal is preserved due to the "virtual pitch" psychoacoustic phenomenon.
5. 扬声器工作原理及软件调试入门