HOTONE Skyline Octa是一款具两种模式的八度音效果器。这两种模式采用了不同的算法，适合不同的情况使用。
The Hotone Skyline Octa stompbox is a dual mode octave effects pedal. The two octave modes utilize separate algorithms, and the tones available from each suit a variety of genres and playing styles.
八度音
八度音是一种特殊的效果，它将输入的吉他信号升高或者降低1个或2个八度，再与原声（Clean）按照一定比例叠加之后，可以得到类似管风琴的音色或更为厚实的音色。
在信号波形的表现上，八度音即将原始的信号的频率增加或者降低一倍。
Octave
In music, an octave represents the interval between one musical pitchand another with half or double its frequency.Octave effects take the guitar signal up or down one or even two full octaves. As it is overlaid on the original (clean) signal and adjustments are made to the proportion of these two tones, what results is a rich and thick sound with qualities similar to an organ. The effect takes the original guitar signal waveform and either doubles it or halves it in terms of frequency. 
原始信号 高八度音 低八度音
Original Signal An Octave Up An Octave Down
DIRTY模式
在数字技术还不够成熟的时候，八度音通常使用一个特殊的模拟电路来实现。这种电路将信号通过一个特殊的触发器电路把频率降低一个八度或二个八度。Octa的DIRTY模式正是模拟了这种经典的模拟电路处理方法，可同时输出低一个八度和低二个八度的效果音。
DIRTY模式音色的特点是比较单纯，听感上类似正弦波。音准很好，没有延时，这样在弹奏时会与原声信号比较贴合。但是限于DIRTY模式的原理，该模式下只能用于单音弹奏，在使用过程中需注意对其他不弹奏的弦进行制音，以免出现不必要的杂音。多弦同时弹奏或较长的延音都可能导致噪声出现，而出现这种杂音的特质正是DIRTY模式名称的由来。
Dirty Mode
Before the advent of digital technology, the octave effect generally relied on special analog circuitry. The circuit took the incoming signal through a certain inversion path, taking the signal frequency down one or two octaves. The Octa DIRTY mode models that kind of classic signal treatment, allowing the instrument to play tones one or two octaves lower than normal.
The resulting DIRTY tone is characterized by an unaffected, sinewave-sounding timbre. The intonation is perfect and there is no lag, so the dual tone feels in sync as you play. Because of this unique circuitry, the DIRTY mode is limited to single note playing; simultaneously playing more than one note will result in extra noise, as will letting a note ring out very long. That’s why we call it DIRTY mode. 
POLY 模式
随着科技的发展，八度音出现了多种实现方法，为了获得比较好的管风琴音色，可以使用变调算法（Pitch Shifter algorithm）来实现八度音。变调算法即利用多普勒效应原理，在时域内通过速度差的方法来得到不同的音高变化的算法。而八度音则是变调算法的一个特例，正好其变调key为八度。
在HOTONE Skyline Octa中，POLY模式即使用了变调算法来实现八度音。Octa提供了一个低八度效果音和一个高八度效果音，有两个旋钮分别控制其音量。与原声混合后，乐手可得到高中低三个音域的声音，通过乐手自己调节，可以带来丰富的音色表现力。
由于POLY模式是通过在时域内对信号进行变调，为了保留原始信号数据的特征，在算法实现时需要将原始信号数据保延时一小段时间。这就造成POLY模式会出现吉他手可以感知到的延时。并且由于变调算法的延时特征，部分音的音高可能出现一定的音调偏差。
尽管基于变调算法的八度音效果有一些原理上的限制，但是这种算法允许乐手使用多根弦的演奏，给乐手更大的演奏展示空间。
POLY Mode
As technology continued to develop, engineers discovered different methods to achieve the octave sound. The Pitch Shifter algorithm was developed in an attempt to capture the characteristics of the organ. Built upon the principles of the Doppler effect, the algorithm could produce changes in pitch by using varying speeds within a certain time domain. Here, the octave effect is simply a function of pitch shifting, creating a full octave shift according to a particular key.
The Hotone Skyline Octa effect uses a pitch shifting algorithm to produce the octave sound in POLY mode. In this mode, Octa delivers an octave up and octave down, each adjustable by dedicated volume knobs. As the original signal is worked in, the musician can enjoy a hi-mid-low triple tiered range, and with so much adjustability, tonal expression is virtually limitless.
Because the original signal is shifted within a certain time domain in POLY mode, the musician will notice a slight delay during play. This is a must if the pedal is to preserve the purity of that signal. Also characteristic of the pitch shifting algorithm is a slight change in the pitch of some notes.
Although there are technical limitations, POLY mode allows musicians to play multiple strings (chords) and thus allows for greater freedom in performance expression.
HOTONE Skyline Octa提供了Dirty和Poly两种模式，适用于不同的应用场合，Dirty模式适合急速、短促、跳跃性强的单音演奏，可以产生厚重的八度音色，使声音更具有立体感和包围感；Poly模式适应性更强，可以使用各种不同的演奏手法，特别擅长风琴模拟，得到温和、顺滑的八度音色。两种模式整合在一起，可以适用于基本上所有吉他手对八度音效果的需求。
The Hotone Skyline Octa stompbox is set to perform in any venue for every genre. DIRTY mode shines in the hands of shredders making face-melting solo runs: it’s thick and dimensional, giving you a sense of being surrounded. POLY mode finds a place across the spectrum of playing styles. When you get the high and low octaves going, you can have the smooth and warm body of an organ. With both DIRTY and POLY octave modes available, this stompbox is ready to satisfy the octave needs of basically every guitarist out there.