錄音優劣之判定：音樂家觀點 vs.音響玩家觀點

 在各種版頁，不時會看到許多「專家」批評某個軟體的錄音不好，用的麥克風太多，如果他來錄音的話，就會如何如何來錄製的言論。對音樂軟體發行稍有認知的話，就會瞭解這其實是很幼稚的想法。以古典音樂的軟體來說，都是要音樂家聽了感到滿意，才能上市發行的。他/她所要的音效，多數情況是最能代表其詮釋演繹，而這會符合發燒友想要的質感，動態，音場嗎？這牽涉到主導的音樂家，錄音師或製作者，想要讓聆聽者聽到什麼樣的音效。

卡拉揚在DG的錄音，就是常被發燒友所詬病的典型例子。說是麥克風用得多，缺乏自然的空間感，動態對比不自然等等。對卡拉揚的音樂生涯有所瞭解，就會知道這是他極力控制各種細節，完美主義作風的一部份。他意欲讓聽者聽到的各聲部平衡，在錄音現場不能達到心目中要的狀態，可以在事後監聽時，經由混音時的操作來到他的要求。這種操作，如果不採用多麥克風多音軌的方式，是很難辦到的。即使錄音師知道這樣的運作在音響效果上會有所犧牲，但首要的目標是滿足指揮/音樂家的需求，否則沒有得到同意，再好效果的錄音也無法發行。

此外還要考慮到的是，大部分音樂消費者所用的器材，並不都是音響玩家級。當我們在注意動態，音場寬深，低頻勁道等方面時，一般人所重視的可能只是聽清楚音樂的演繹，特別是主奏聲部或樂器的音符。音效負責人在如此考量之下，除非是要發行市場很小的發燒碟，否則不太可能專門對發燒友特別照顧。對照之下，許多發燒友所認可的錄音，可能湊巧是主導的音樂家對音效的認知與錄音師接近，或者純粹信任專業的判斷，所以就不過度干涉。近年柏林愛樂發行的黑膠片，以兩支麥克風來收音，應該就是屬於這種情況。也可能像是以前的Mercury，後來的Telarc 錄音，本質上就是發燒品牌，因此以音效的考量為優先。

以小提琴協奏曲來說，許多發燒友第一次在現場聽到，幾乎都會訝異於小提琴的音量與形體之小，與一般聽到的錄音相差甚多，甚至覺得非常不習慣。會有這樣的差異，很大的可能性是，小提琴家在演奏時所聽到的琴聲比例，也是她/他們想讓聽眾體驗到的，所以就要讓小提琴錄得相當「大支」。而如果錄音呈現的是在音樂廳裡，常聽見的「小支」琴聲，在一般音樂消費者所用解析力不高的器材聽起來，許多人應該都會抱怨聽不清楚獨奏部分。

 再以鋼琴錄音來討論，在鋼琴協奏曲的場合，雖然琴聲的比重會比現場聆聽要大一些，但多數不像小提琴協奏曲那麼明顯。而在鋼琴獨奏的錄音，值得探索的是為何常要用到多支近距離，還有加上另外收錄堂音的麥克風。如果錄得像在音樂廳裡觀眾座位上，聽到自然的鋼琴大小與遠近，不是很好嗎？這種錄音算是極少數，大多還是把各種近距離細節如敲擊機構動作及演奏者的呼吸等都收錄進去。這樣所得到的強音動態效果，是現場很難感受到的。或許這是多數鋼琴家所願，大眾會喜歡的呈現吧。

音響器材在使用時所面臨的震動來源及影響

音響器材在使用時所面臨的震動來源，大致可分為外界環境傳來及各器材本身所產生。

外來的震動，經由固體介質像是馬路，建築物，音響架等傳來的，穿透能力強且傳播速率高。但因為頻率很低，一般人多半沒有感覺。其實以醫用聽診器，放在器材表面仔細聽一下，就可以聽到一些遠方傳來的不明低頻震動。藉此可以延伸想像，周遭還存在更多聽不到的，更低頻率震動。例如建築本身的晃動，頻率約在0.1Hz到 5Hz的範圍。地面及樓層地板的共振，約是5到50Hz。各種建築裡的空調，電梯等機械器材發出的噪音，在10到500Hz的範圍。而來自建築外的交通工具，約在15到100Hz。至於環境裡的聲波像是各種噪音，經空氣傳來的，由於穿透能力有限，傳遞的距離不遠，所以到達室內之後多數已經衰減，造成的影響算比較小。

而音響器材本身產生的震動，最大的來源當然就是喇叭發聲。最快速的傳遞途徑也是透過各種固體介質，從地面，牆壁，音響架等傳播到器材。而當器材與發聲的喇叭處於同一空間時，又會經由空氣聲波傳播而到達器材。其它有馬達的器材，如黑膠唱盤，數位光碟播放機，使用時的轉動也是產生機械震動的主要來源。另外，各種器材電源部分的變壓器，也必然會有震動的產生。更細小的震動，則是在電流通過電子元件時，由於「逆壓電效應」（inverse piezoelectric effect）而產生極微小的震動。

因此，一個音響系統在播放時，並不是只有表面可見的喇叭震動。還有受到許多細微，人的感官無法察覺的微小震動的影響，不論是外來或內部產生，其實無所不在。

黑膠的播放，本身就是將溝槽裡的資訊，經針尖運動轉換成電能訊號。任何溝槽內不該有的，多餘的震動，都會被唱頭拾取，進入系統被放大。即使耳朵無法直接聽到，也會形成背景底噪，並造成放大線路及喇叭的額外負擔，一方面使失真率提高，一方面也浪費功率。

而除了黑膠播放系統之外，以其它各種器材裡的電子零件來來說，特別是電容器，都或多或少有壓電效應（piezoelectric）的性質。也就是說，在受到壓力或震動時會產生電能，與訊號混雜在一起，形成失真。再從更微觀的分子角度來看，任何物質接受到外來震動能量，表面上雖然只會短暫的隨之震動，然而能量卻不是馬上消逝，而在分子之間鏈結像彈簧似的，繼續來回震盪一段時間。

這些微小的震動，與通過的訊號強度如果越接近，就越容易產生交互作用，形成干擾的效應。換句話說，整個播放鏈裡，訊號強度越小的環節，對小震動越敏感。像是黑膠唱盤，昇壓器及放大黑膠訊號的唱放，就會特別容易受到微小震動的干擾。這也是在器材下放不同的墊材，聲音就會立即改變的原因。

在音響市場上，針對震動處理而推出的產品不勝枚舉。在瞭解到其本質之後就會發現，絕大多數都規避了問題的核心，嚴格來說都只能算是調聲器具（tuning devices）而已。像是剛性的角錐類產品，對低頻的作用極其微小，傳過這類墊材之後幾乎沒有任何衰減。而在稍有效果的較高頻率，也只有縱方向震動有些效果，對其它方向的震動可以說束手無策。

事實上，避震除震器材的效果，只要用儀器測試就很清楚，在某個震動頻域可以減低多少分貝或百分比。但是，各種音響用的器材架及墊材，卻從未曾見過廠家敢發表測試數據。之前我在這專欄曾介紹過美國Newport公司的氣浮平台，Minus K的高科技機械式避震平台，以及倉敷與Acuurion主動除震平台。這些器材原本設計是用在精密度極高的光學，半導體，及物理化學實驗等用途，它們的避震效果絕對不是隨便吹牛的，而是明明白白提供數據，顯示在何種狀況，處理哪些頻率的震動有多大效果。假如它們的避震效能不合規格，早就被淘汰，無法在高度競爭的精密工業界生存下去。此外，這些高科技器材雖然貴，但去計算它們的研發，製造及出廠前測試的成本，利潤比例卻比一般音響器材低很多。還有，它們不需要刊登廣告打知名度，也不必追求富麗堂皇的外觀，不像音響器材廠商還要加上這方面的可觀成本。

Anti-Skating and Side Force, Part#1: Classification of Various Side Forces during Vinyl Record Playback

＊＊＊（中文版請參閱：https://bingrungtsai.blogspot.com/2021/10/blog-post.html）＊＊＊

As we view from the front side of a cartridge playing a record, the side forces exerted on the cartridge's stylus/cantilever will be parallel to the record surface, and (mostly) perpendicular to the cantilever. For easier discussion below, the direction for side force toward the center of the record is termed "inward", whereas the direction toward the rim of the record is "outward".

During vinyl playback, given proper tracking force setting, the majority of tracking distortions or "break ups" are due to the existence of persistent side forces causing uneven loads to the damper in a cartridge.  When the damper, like a spring compressed to the limit of its normal operating range, cannot accommodate the cantilever moving in certain direction, the stylus will fail to follow the trajectory of groove modulations. In other words, in such situations, the damper is not able to yield further to allow the cantilever to move freely, as such the stylus cannot trace the signal properly, and distortions occur. Only in uncommon situations the distortions result from groove modulations surpassing the tracking capability of the cartridge, mainly seen in cartridges with unusually stiff dampers. 

The characteristics of side forces can be divided into two major categories. In the first category, the direction of the force alters at about 1/20 second or longer period, or even not changing direction at all for the entire side of the record. This directional-change rate is at or below the low-frequency resonance of the cartridge-arm combo, hence such force CANNOT be effectively absorbed by the damper in the cartridge, thus propagates between the tone arm and the cantilever of the cartridge and is stored in the cartridge's damper as potential energy. This category will be termed "DC-mode" side force, for its similarity to the Direct Current in electricity which the current flow does not change direction.

In the second category, the direction of the force alters rapidly, similar to the AC electricity. Such side force manifests as kinetic energy and is quickly stored and then released by the damper in the cartridge.

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Category of side forces, Group 1:

(1A) When playing a record, each side of the stylus contacts the groove wall and generates frictional forces. The forces drag the cantilever forward as in Figure.1. In most cases, the extended straight line from the cantilever does not precisely coincides the pivot point of the tone arm, a torque force is therefore generated which pushes the arm assembly in or outward.

(1A-1) For pivoted arms (either conventional or tangential) with an offset angle, as in Figure.2 below, the drag on the cantilever generates forward force (red arrowed line) , together with the blue line indicating the moment arm, generates inward torque acting on the tone arm.

 (1A-2) In linear tangential arms or straight pivoted arms, both without offset angle, if the cantilever of the installed cartridge is not precisely pointing toward the pivot center, the drag on the cantilever during play can still generate inward or outward torque on the arm. 

(1B) When the spindle hole of the record is off centered, the rotation of the record will bring the cartridge and arm assembly inward and outward alternatively at about 1.8 second interval, hence generating side forces.

(1C) The surface of a record is not entirely level, causing uphill and/or downhill effects as the cartridge plays and the arm moves toward the center spindle.

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Categoriy of side forces, Group 2:

(2A) As a stylus interacts with both groove walls, especially for stereo records where the two walls are engraved with different signals, the two contact sides of the stylus may take on forces of uneven magnitudes, generating rotational torque on the stylus shank, then propagating upward to the cantilever. Depending on the signal contents, such torque can quickly appear, disappear, and the rotation can reverse directions, all in very short period of time. The time window is typically much less than 1/20 second. The damper mechanisms in most cartridges can easily absorb such transient torque force, and prevent further propagation upward to the arm.

(2B) When playing musical signals, the stylus will move along with the groove walls back and forth, with frequency range from around 20Hz to more than 20kHz. The force and energy acting on the stylus propagates upward and will mostly be absorbed by the cartridge damper. 

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In general, the two major groups of side forces coexist during play. (1A) is a much greater and more persistent source of side force than (1B) and (1C). And Group 2 side forces are not only weaker, but also transient in nature and are nearly entirely absorbed by the damper.

Consequently, Group 1 side forces should be the focus for further research and discussion. (1A), (1B) and (1C) types of forces may add or subtract to one another, although (1A)  which includes (1A-1) and (1A-2), remains the most dominant and influential of all. Consequently, the design and adjustment of anti-skating mechanisms in pivoted arms and the minimization of side forces in linear tracking arms should consider these as critical factors. 

Group 2 forces are absorbed by the damper, consequently changes in their intensities will not affect the tone arm. This in term implies the difference in signal strengths do not change the required amount of anti-skating force in pivoted arms. 

Incidentally, since the amount of dynamic friction force is near constant at low speeds, the friction generated between the stylus and groove walls remains unchanged for outer grooves and inner grooves, even though the relative linear speed is reduced by half. As such the applied anti-skating force should ideally stay constant during play for pivoted arms. More in-depth discussions on this subject will continue in a future write-up.