Frequency Response 頻率響應為什麼重要?

Response of Neumann KM184 Mic

        頻率響應規格大概是音響中幾個基本的規格之一.  在家用音響的領域, 喇叭與空間是決定頻率響應表現最關鍵的因素.  因為現在的擴大機, 訊源設計的頻率響應規格都可以做到非常平坦.  (註: 黑膠唱盤必須小心確認, 但現實上, 鮮少發燒友真正確認量測結果, 通常都是"耳朵"說話....更可悲的是, 沒有幾家廠商開放調整的空間給使用者)

        專業錄音工程當然不能如此.  從Mic開始一路到錄音設備, 甚至鑑聽系統, 無不需要校正已達到一定平坦的頻率響應規格, 以避免扭曲音源.  其實許多發燒友"形容"音響表現的說法, 其實大部分都隱藏在響應之中.  我節錄Neumann在說明低中高頻段在"音色"上的描述:

    Below 40 Hz: Sub Bass. Apart from kick drum, the sub bass range contains little musical information.

    40-200 Hz: Bass frequencies, the foundation. The lowest note of a 4-string bass is about 40 Hz, the lowest note on a guitar is about 80 Hz. The lowest note of a male singer (baritone) is about 100 Hz, although you rarely hear such low notes. Well, maybe from country singers. Most pop singing by men and women is above 150 Hz.

    200-500 Hz: Low Mids. This is the “body” of most instruments. This is also where the human voice has most of its energy.

    500-3000 Hz: Mid Range. This area is crucial for the sound character, because it’s where the human ear is most sensitive to even the smallest details. The telephone transmits little below or above this range, yet we are able to recognize callers by their “hello.”

    3000-7000 Hz: Presence. This range is important for sound definition and good intelligibility. It is the area of many speech consonants.

    7000-14000 Hz: Treble. This area is crucial for our sense of brightness. However, too much energy in this area can sound harsh and distracting. This is the area of speech sounds such as S and T, of cymbals, but also of string noises.

    Above 14,000 Hz: Air band. This area is important for recordings that want to sound “expensive” and “super-hi-fi.” It gives voices and stringed instruments an airy feel, hence the name. It does not contain much musical information, though.

        當然響應至少有兩個面向, 一是寬度, 一是Level.  一般人的音響系統很難達到Sub bass領域.  能夠平順延伸到40Hz已經是很夠了.  現今喇叭設計在高頻響應上, 達到20kHz也不是太大問題.  大部分發燒友面對響應的問題, 主要是響應的不均勻!!

        專業麥克風追求響應平坦, 我想原因很直接, 就是希望不扭曲所錄音的音樂.  那發燒友追求"一定程度"的平坦, 自然也是希望"忠實"重現音樂.  如果你的系統在100Hz下快速滾降, 以量感來說, 原本交響樂團裡編制的10把大提琴就"縮編"到5把.  如果高頻量感過大, 一樣的道理, 第一第二小提琴數量自然"激增".  了解古典音樂的樂友自然知道, 作曲家在作品中對樂器的編制, 指揮家精心調整的音域平衡所代表音樂的意義.  Stereo Sound前主編菅野所形容的"音響指揮家", 看似說明了發燒友在自己音響系統中"至高"的地位; 或許其實(我猜的)是在"暗諷"發燒友的"各行其是".  當然, 這樣的說法對音響市場的蓬勃發展應該是有正面激勵的作用.

        頻率響應很重要, 但對大部分的發燒友(我也在其中)很難!!  那怎麼辦?  總不能大家搞到和專業錄音室一樣, 也不是每個人都有這樣現實的能力!  要多平坦?  哪個頻段比較重要?  下回分解.