1. SPL: sound pressure level
SPL是聲壓級的縮寫，是響度的傳統表達方法。其單位是dB SPL。設定20uPa對應於0dB SPL，這也基本是聽域的下極限。聲壓隨着與聲源距離的增加而降低，5英尺距離正常的說話聲平均大致為60dB SPL。 聲壓為1Pa時，相當於20log(1/0.000020)=94dB SPL 聲壓為1uPa即0.1Pa時，相當於74dB SPL 傳聲器靈敏度的參考聲場壓力為94dB SPL。在空氣中參考聲壓p(ref）一般取為2*10E-5帕，這個數值是正常人耳對1千赫聲音剛剛能覺察其存在的聲壓值，也就是1千赫聲音的可聽閾聲壓。一般講，低於這一聲壓值，人耳就再也不能覺察出這個聲音的存在了。顯然該可聽閾聲壓的聲壓級即為零分貝。
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. 揚聲器工作原理及軟件調試入門