Japanese vowels are commonly referred to as "short vowels" because of their tendency to be voiced rather quickly and indiscreetly. It's for this reason that vowels such as "i" and "u" are, in many instances, muted or removed from speech, altogether. When we talk about long vowels, on the other hand, we're referring to just that ~ a phenomenon in speech where vowels are sounded more clearly than they otherwise would be.
The Phonetics of a Long Vowel
If you can recall from the previous lesson on timing, syllables always get a single count, even the syllabic "n". Long vowels, on the other hand, extend existing vowels by a single count, giving them 2 counts. Take a look at the long "u" sound in the following example:
練習 > れんしゅう > renshû = re(1) + n(1) + shu(1) + u(1)
re + n + [shu + u] = re + n + shû(2)
Here, we can break up the word "renshû" into its principle syllables, namely "re+n+shu+u". In this sense, each component gains a single count. Upon closer inspection, however, the last "u" syllable is consistent (or the same) as the vowel in "shu". This causes a "stretching" of the vowel sound, giving it twice the duration it would have had if it weren't there. This "stretching" is what we mean by the long vowel, it is an extended vowel sound.
This "repetition" of a vowel sound occurs primarily for the vowels "i" and "u", as in the following examples:
うれしい > ureshii > 4 counts
九州 > きゅうしゅう > kyûshû > 4 counts
Note that the macron is placed on top of the "u" for long "u" vowel sounds, but not on the "i". This is one of several peculiarities in the Hepburn system of Romanization, which you can review here.
The long vowel for "e" and "o", however, do not follow this idea of "repetition":
先生 > せんせい > sensei > 4 counts
京都 > きょうと > kyôto > 4 counts
The long vowel for "e" is seen with an "i" vowel, instead of an "e" vowel, while the long "o" vowel is seen with a "u" vowel. Simply put, they look like "ei" and "ou" when seen in the kana. This peculiarity has much to do with the nature of pronouncing the long vowel for these particular vowels, which will be explained later.
The long vowel for "a" exists only in loan words, but any of the vowels may have long vowel sounds in foreign loan words:
ドライバー > doraibaa > 5 counts
ベリーブ > berîbu > 4 counts
ブルー > burû > 3 counts
パレード > parêdo > 4 counts
ゴール > gôru > 3 counts
In summary, long vowels are prolonged vowel sounds, meaning they simply extend the vowel sound of the previous syllable by a single count. This means you spend 2 counts when you say the vowel sound of "u" in "shû", for example.
Pronouncing Long Vowels
It was mentioned that the Japanese vowel is very indiscreet. Many times, it's just a hum that gives the speech its pitch. For that purpose, prolonging these sounds by using long vowels simply makes these otherwise quiet vowels more discernible in speech. In other words, the once relatively mute "i" and "u" becomes a jabbed "EE" and "OO" that is distinct and noticeable, even to the foreigner.
For many reasons, it is good to view Long Vowels as accents in themselves, in the sense that they add stress to the vowels they stretch. Note, however, that this does not mean that their volume is increased; rather, it means that the vowel sound is brought forward by the mere fact that you give more time in sounding out a long vowel than you do a normal, short vowel. This can be likened to the accent in the English word "Believe", in that the accent lies in the second syllable, "bi-LEE-vuh". It's amusing, therefore, to note that the katakana equivalent of this word actually DOES have long vowel on this syllable, "ベレーブ".
The long vowel, therefore, is simply a prolongation of the previous vowel sound by a single count, the effect of which is a highlighting of certain vowel sounds in a word. For all foreign loan words, you can do this, but for native Japanese words with long "e" and "o" vowel sounds, a certain nuance should be noted. The long "e", for example, sounds like a hybrid between an "e" and "i" sound, while the long "o" sounds like a hybrid between the "o" and "u" sound. This is very minute, but try listening to words with long "e" and "o" sounds and note the slight difference in simply elongating the sound, altogether.
If there is anything to remember, however, it should be to avoid reading out long "e" and "o" sounds as they appear in hiragana. Since the long "e" vowel is written as "えい", many people have the urge to speak it with a rising intonation, as you would in the English word "ray". It is wrong, therefore, to pronounce the word "sensei" as "sen-SAY". Similarly for the long "o", the written form "おう" tends to make people pronounce it with a rising intonation, as in the English word "toe". The long "o" vowels in "tôkyô" for example should not be pronounced as "TOE-KYOWE".
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