Japanese Voice to Text — 日本語音声テキスト変換
Japanese is arguably the most technically complex language for speech recognition of any major world language. It is written in three interlocking scripts simultaneously. It has no spaces between words, so the model must segment a continuous stream of characters into meaningful units. It has a pitch accent system where the same string of sounds means different things depending on which syllable rises. And it has more homophones than almost any other language — words that sound identical but require completely different kanji depending on meaning. This page explains exactly how Japanese voice recognition handles all of it, and how to get the best output from wherever you're dictating.
日本語の音声認識は技術的に最も複雑です。三種類の文字体系、単語間のスペースなし、ピッチアクセント、そして膨大な同音異義語。このページでは、音声入力がどのように機能するか、そして最良の結果を得るための方法を詳しく説明します。
Three Scripts Simultaneously — 三種類の文字体系
Japanese is the only major language that routinely uses three distinct writing systems in a single sentence. When you dictate in Japanese, the speech model must decide — in real time — which script each word should be written in:
ひらがな Hiragana
The phonetic syllabary for native Japanese grammar — verb endings, particles (は, が, を, に), function words, and words without established kanji. "食べている" — the verb stem "食べ" is kanji, but the conjugation ending "ている" is hiragana. The model outputs hiragana for particles and grammatical elements automatically.
カタカナ Katakana
Used for loanwords from foreign languages, foreign names, onomatopoeia, and technical terms. "コンピュータ" (computer), "スマートフォン" (smartphone), "アメリカ" (America). The model must recognise that a foreign-sounding word should be output in katakana — and choose the correct conventional katakana spelling, which is not always phonetically predictable.
漢字 Kanji
Chinese-derived characters used for content words — nouns, verb stems, adjective stems, proper nouns. "会議" (kaigi, meeting), "電話" (denwa, telephone), "東京" (Tokyo). A single phoneme sequence may correspond to multiple kanji with completely different meanings — this is the homophone disambiguation problem, explained below.
Example: one sentence, three scripts working together
会議で田中さんがプレゼンを発表しました。
■ Kanji ■ Hiragana ■ Katakana — all in one sentence
No Spaces: The Word Segmentation Problem — 分かち書きなし
In English, word boundaries are marked by spaces. In Japanese, they are not — spoken or written. "今日会議があります" (Today there is a meeting) is written as a continuous string of 11 characters with no spaces. The speech model must simultaneously transcribe phonemes, assign each phoneme sequence to the correct script, and segment the continuous acoustic stream into individual words — all at once.
This segmentation step is where most Japanese ASR errors originate. The model uses a language model (a statistical understanding of which word sequences are likely in Japanese) to decide where one word ends and another begins. For standard vocabulary in normal sentence structures, this works very well. Where it fails:
Proper nouns and names
Uncommon surnames and place names have no established segmentation pattern. "山田" (Yamada) is straightforward; "鴨志田" (Kamoshida) may be split or mis-kanji'd. Always check proper nouns.
Compound words vs. separate words
"気になる" (ki ni naru, to be concerned) vs. "気に入る" (ki ni iru, to take a liking to) — the segmentation determines the kanji. Fast speech makes these harder to disambiguate.
Technical and specialist vocabulary
Domain-specific compound nouns — medical, legal, engineering — may be split into their component words rather than recognised as a single unit. "骨粗鬆症" (osteoporosis) may be mis-segmented.
Sentence-final particles in fast speech
The particles ね, よ, か, わ, な at the end of sentences can be swallowed in fast speech. The model may drop them or attach them to the preceding word incorrectly.
The Homophone Problem — 同音異義語：日本語最大の難問
Japanese has more homophones than almost any other language. Because kanji were assigned to phonetic Japanese readings over centuries, many completely unrelated words share the same pronunciation. The speech model must choose the correct kanji for every content word based entirely on context — with no acoustic information to distinguish them.
| Sound | Kanji options | Meanings | ASR risk |
|---|---|---|---|
| きかん (kikan) | 期間 / 機関 / 気管 | Period / Organisation / Trachea | Medium — context usually clear |
| かいじょう (kaijō) | 会場 / 海上 / 解錠 | Venue / On the sea / Unlocking | High — in ambiguous sentences |
| こうしょう (kōshō) | 交渉 / 工匠 / 口笑 | Negotiation / Craftsman / (rare) | Medium |
| しんこう (shinkō) | 進行 / 信仰 / 振興 | Progression / Faith / Promotion | High — context-dependent |
| いし (ishi) | 意思 / 医師 / 石 / 意志 | Intention / Doctor / Stone / Will | Very high — four options |
| かんしん (kanshin) | 関心 / 感心 / 歓心 | Interest / Admiration / Favour | High in formal writing |
How to reduce homophone errors
Provide context sentences — the model makes better kanji choices when the topic is established. "医療に関して話します。今日のテーマは医師の役割です" gives the model enough context to correctly choose 医師 (doctor) over 石 (stone) for "ishi." Starting dictation mid-thought without context leads to more homophone errors.
Pitch Accent — ピッチアクセント：音声認識への影響
Japanese is a pitch accent language — words are distinguished by the pattern of high and low pitch across their syllables, not by stress as in English. The word "橋" (hashi, bridge) has a different pitch pattern from "箸" (hashi, chopsticks) and "端" (hashi, edge) — all spelled and pronounced with the same consonants and vowels, differentiated only by which syllable is high-pitched.
Modern Japanese ASR systems use pitch as one input signal for disambiguation, but they do not rely on it as the primary cue — context does more work than pitch in most models. This means pitch errors in a speaker's Japanese (common for non-native speakers and speakers from dialects with different pitch systems) usually don't cause transcription errors as long as context is clear. The kanji selection is made primarily from lexical context, not pitch alone.
Tokyo pitch accent — same phonemes, different pitch patterns
橋 (bridge)
ha-SHI
Low-High
箸 (chopsticks)
HA-shi
High-Low
端 (edge)
ha-SHI
Low-High (context)
Keigo — 敬語：Speech Level and Voice Recognition
Japanese has an elaborate system of speech levels called keigo (敬語) — different verb forms, vocabulary, and grammar depending on the social relationship between speaker and listener. The three main levels are teineigo (丁寧語, polite), sonkeigo (尊敬語, respectful — elevating the other person's actions), and kenjōgo (謙譲語, humble — lowering your own actions). Each uses completely different verb forms for the same action:
| Register | "To eat" (食べる) | "To go" (行く) | ASR accuracy |
|---|---|---|---|
| Casual (informal) | 食べる / 食べた | 行く / 行った | ✅ Very good |
| Polite teineigo | 食べます / 食べました | 行きます / 行きました | ✅ Very good |
| Respectful sonkeigo | 召し上がります | いらっしゃいます | ✅ Good for common forms |
| Humble kenjōgo | いただきます | 参ります / うかがいます | ⚠️ Moderate — rare forms may error |
| Business keigo compounds | 拝見いたします | お伺いさせていただきます | ⚠️ Long forms occasionally split |
The model handles standard teineigo and common sonkeigo/kenjōgo forms reliably — these are heavily represented in business email and document training data. Where it struggles is hyper-formal business keigo compounds like "お伺いさせていただきます" — the longest humble forms may be split or partially mis-kanji'd. For these, type them manually or dictate slowly and verify.
Japanese Dialect Accuracy — 方言の認識精度
Standard Japanese (標準語, hyōjungo — effectively the Tokyo dialect as codified for broadcasting) is what all ASR models are trained on. Regional dialects vary significantly — from minor accent differences to mutually incomprehensible speech:
Tokyo Standard / NHK Japanese — Best
The accent and phonology of educated Tokyo speakers — particularly the flat (atamadaka or heiban) pitch patterns and clear consonant articulation — is the reference model. NHK news-style Japanese gives word error rates of 5–10% in quiet conditions. If you speak standard broadcast Japanese, expect excellent accuracy.
Kansai-ben (Osaka/Kyoto/Kobe) — Moderate
Kansai dialect has a completely different pitch accent system from Tokyo (Kyoto-Osaka type vs Tokyo type), distinct vocabulary ("ちゃう" for "違う," "なんでやねん," "めっちゃ"), and different grammar ("〜へん" negative instead of "〜ない"). Models handle Kansai-inflected standard Japanese acceptably, but heavy Osaka-ben causes higher error rates — particularly the pitch mismatches. Kansai speakers doing formal dictation should approximate standard Japanese.
Hakata-ben (Fukuoka) — Moderate
Hakata dialect from Fukuoka is relatively well-represented in media (popular TV dramas, comedians) and thus in training data. Distinctive features like "〜と？" for "〜ですか？" and "ばい/たい/けん" sentence endings cause occasional errors. Vocabulary diverges less than Kansai from standard, so accuracy is moderate-to-good with clear speech.
Tohoku-ben (Northern Japan) — Challenging
Tohoku dialects (Aomori, Akita, Yamagata, Sendai) are historically the hardest for ASR. A distinctive feature is the collapse of the /i/ and /ɯ/ (u) distinction — making "shi" and "su" sound identical — combined with vowel devoicing patterns and distinct vocabulary. Speakers from northern Japan doing formal dictation should approximate standard Japanese as much as possible.
Okinawan Japanese — Challenging
Ryukyuan languages (Okinawan, Miyako, Yaeyama) are considered by linguists to be separate languages from Japanese, not dialects. "Okinawan Japanese" — the variety of standard Japanese spoken with Ryukyuan influence — has vowel mergers (/e/ → /i/, /o/ → /u/ in Ryukyuan languages) that affect Japanese pronunciation. Standard ASR models handle modern Okinawan Japanese reasonably, but older speakers with stronger Ryukyuan features will see higher error rates.
Non-Native Japanese — Variable
Japan's growing international resident population includes many non-native Japanese speakers. Error rates vary significantly by first language — Chinese L1 speakers generally have the lowest error rates (similar phoneme inventory, pitch familiarity), followed by Korean L1 (similar morphology, different phonology). English L1 speakers often struggle with long vowel length, geminate consonants (っ), and the /r/ phoneme that has no English equivalent.
使い方 — How to Start
言語メニューから「Japanese (日本語)」または「ja-JP」を選択してください
Select Japanese (ja-JP) from the language menu. Chrome on desktop gives the best Japanese recognition — it uses Google's Japanese ASR engine which is among the best available.
「Start 🎤」をクリックしてマイクのアクセスを許可してください
Click Start and allow microphone access. Ensure you are in a quiet environment — Japanese segmentation errors increase significantly with background noise.
自然なペースではっきりと話してください。文を完全に終えてから間を置くと精度が上がります
Speak at a natural pace, completing full sentences before pausing. The model uses sentence context for kanji selection — incomplete sentences lead to more homophone errors.
テキストをコピーするか、TXTファイルとしてダウンロードしてください。句読点（。、）は自動的に挿入されます
Copy text or download as TXT. Japanese punctuation (。、) is inserted automatically. Furigana is not added — the model outputs standard kanji without reading aids.
Katakana Loanwords — カタカナ語の扱い
Japanese incorporates foreign vocabulary (primarily English) as gairaigo (外来語) — loanwords adapted to Japanese phonology and written in katakana. This creates a specific challenge: the same English word may have multiple established katakana conventions, and the phonological adaptation can be so heavy that the connection to the source word is obscured.
Common tech loanwords — usually correct
computer → コンピュータ / コンピューター
smartphone → スマートフォン / スマホ
meeting → ミーティング
deadline → デッドライン
password → パスワード
Tricky cases — check these
Words with variant spellings: コンピュータ vs コンピューター (long vs short final vowel)
Words abbreviated in Japanese: パソコン (pasokon) for personal computer — the full form may not be recognised
New English tech terms not yet in the training data may be output as phonetic hiragana rather than katakana
Foreign names: unusual name katakana conventions are idiosyncratic and the model may use an alternative reading
Numbers and Dates — 数字と日付
Japanese has two number systems — Sino-Japanese (ichi, ni, san... based on Chinese readings of kanji) and native Japanese (hitotsu, futatsu, mittsu... for counting objects) — plus the option to output Arabic numerals. Speech recognition outputs Arabic numerals by default for cardinal numbers (5, 10, 2026), which is standard in modern Japanese digital writing. Watch for these specific cases:
Large numbers
Japanese groups numbers in units of 万 (10,000) not thousands. "一億円" (100 million yen) — dictate "いちおくえん" and the model outputs 1億円 or 100,000,000円. Verify large financial figures.
Dates
Japanese uses year-month-day order. Both the Western calendar (西暦) and the Japanese imperial era system (和暦 — Reiwa, Heisei etc.) are used. Saying "令和7年" (Reiwa 7 = 2025) will output the era name correctly. Saying "2025年" outputs the Western year.
Counters
Japanese uses different counter words for different objects: 3冊 (books), 3台 (machines), 3枚 (flat objects), 3匹 (small animals). The model selects the correct counter kanji based on context — it usually succeeds for common objects, may fail for unusual categories.
精度を高めるためのヒント — Tips for Best Japanese Accuracy
✅ 精度が上がること
- • 文を最後まで言ってから間を置く — 途中で止めると漢字変換が崩れる
- • 同音異義語の多い話題はコンテキストを先に述べる
- • 固有名詞（人名、地名）は丁寧に発音する
- • 方言話者は標準語に近づけて話す
- • 静かな環境でマイクを使う — 雑音はセグメンテーションに影響
- • ChromeブラウザはJapanese ASRの精度が最も高い
- • 長い複合語はゆっくりはっきり発音する
⚠️ よくあるエラーと対処法
- • 同音異義語の誤変換 — コンテキストを与えるか、後で手動修正
- • 固有名詞の漢字誤り — 人名・地名は必ず確認
- • カタカナ語のバリエーション — コンピュータ/コンピューターなど
- • 敬語の長い複合形 — ゆっくり話すか手動入力
- • 関西弁・東北弁 — 標準語で話すと大幅に改善
- • ふりがな — 音声認識では出力されないため手動で追加
Who Uses Japanese Voice to Text — 利用シーン
Business Professionals
Japanese office workers use voice dictation for email drafts, meeting minutes, and reports. Typing Japanese on a keyboard requires IME conversion (typing romaji, selecting kanji) which is significantly slower than typing English. Voice dictation bypasses the IME step entirely — speak, get kanji output directly.
Students and Researchers
University students dictate essay drafts, seminar notes, and research summaries in Japanese. Researchers use voice dictation for literature review notes. Dictating formal Japanese and cleaning up kanji errors is faster than typing long-form academic Japanese from scratch.
Writers and Bloggers
Japanese bloggers, light novel writers, and content creators use voice dictation for first drafts. Japanese has a strong culture of light novels and web fiction — fast output volume matters, and voice dictation significantly increases words-per-minute for Japanese composition.
Japanese Diaspora
Japanese speakers in the US, Australia, UK, and Brazil use voice dictation for communication with family in Japan, official Japanese documents, and community work. Typing Japanese on a non-Japanese keyboard requires IME setup — voice bypasses this entirely.
Japanese Language Learners
Advanced Japanese learners use voice-to-text as a pronunciation feedback tool — if the model correctly transcribes what they said, their pronunciation was accurate. Misrecognition reveals where pronunciation needs work. Particularly useful for distinguishing long/short vowels and geminate consonants.
Mobile Users
Japanese smartphone users compose LINE messages, tweets, and emails via voice. Flick input (the standard Japanese mobile keyboard method) is fast but requires learned muscle memory — voice dictation is an alternative that many users prefer for longer messages.
日本語音声コマンド — Voice Commands in Japanese
Say these during dictation to add punctuation. Note that Japanese punctuation (。、) differs from Western punctuation:
Punctuation / 句読点
| 言う / Say | 挿入 / Inserts |
| "句点" / "まる" | 。(Japanese full stop) |
| "読点" / "てん" | 、(Japanese comma) |
| "疑問符" | ？ |
| "感嘆符" | ！ |
| "コロン" | ： |
| "中点" | ・(interpunct) |
| "かっこ開く/閉じる" | 「 」(Japanese quotes) |
Format / 書式
| 言う / Say | 動作 / Action |
| "改行" | New line |
| "段落" | New paragraph |
| "削除" | Delete last word |
Japanese quotation marks
Japanese uses 「corner brackets」not "speech marks." The model usually outputs 「」for quoted speech automatically when the sentence structure implies a quotation. If pasting into Word, verify quotation mark style.
日本語音声ファイルを文字起こし — MP3, WAV, MP4
Upload Japanese audio recordings — meetings, lectures, interviews. Pro plan handles files up to 5 hours with timestamps. / 会議録音やインタビューをアップロードして、日本語テキストを取得できます。
よくある質問 — FAQ
Does it output kanji automatically, or just hiragana?
It outputs full Japanese text with kanji, hiragana, and katakana — just as you would write normally. You don't get raw hiragana that you then need to convert. The model does the kanji selection in real time based on context. For common vocabulary in clear sentences, kanji selection is accurate. For homophones in ambiguous sentences, you may need to correct the kanji manually after dictation.
ふりがな（ルビ）は自動的に付きますか？
いいえ。音声認識は漢字テキストを出力しますが、ふりがなは自動的に付きません。ふりがなが必要な場合（子供向けの文章、教材など）は、Word の「ふりがなの表示」機能や、専用のふりがなツールを使って後から追加してください。音声入力後の手動作業になります。
How does it handle Japanese proper nouns — names and place names?
Common surnames (田中、鈴木、佐藤、山田) and well-known place names (東京、大阪、京都、北海道) are transcribed correctly. Less common surnames — particularly those with unusual kanji or multiple possible readings — are a known weak point. The model will output the most statistically common kanji for that phonetic reading, which may not match the actual person's name. Always verify personal names and unusual place names. For documents where name accuracy is critical, type proper nouns manually.
関西弁で話しても認識されますか？
関西弁でも基本的な会話は認識されますが、誤りが増えます。特にピッチアクセントの違い、「〜へん」「ちゃう」「なんでやねん」などの関西特有の表現、そして語尾の違いが影響します。正確なテキストが必要な場合は、標準語（東京方言）に近い話し方をすることをお勧めします。大阪弁の特徴的な語彙は、標準語の同義語に置き換えて出力される場合があります。
Can non-native Japanese speakers use this effectively?
Yes, with effort. The model is trained on native Japanese speech, so non-native accents cause more errors. The most common issues for non-native speakers: long vowel length (the distinction between おばさん/obāsan and おばあさん/obāasan — aunt vs grandmother — depends on vowel length), geminate consonants (っ — the double consonant in きって/kitte vs きて/kite), and the Japanese /r/ (a flap that is neither English /r/ nor /l/). Using this tool as pronunciation feedback is a valid study method — if the model transcribes correctly, pronunciation was adequate.
iPhoneやAndroidのスマートフォンでも使えますか？
はい。AndroidではChrome、iPhoneではSafariで動作します。AndroidのChromeが日本語認識において最も高い精度を発揮します。インストール不要で、ブラウザ上で直接動作します。スマートフォンで長文のLINEメッセージやメールを日本語で入力する際に特に便利です。フリック入力より速い場合が多く、長文の作成に適しています。
What is the biggest single thing I can do to improve Japanese transcription accuracy?
Complete your sentences before pausing. In Japanese, the verb comes at the end — the model uses the full sentence structure, including the verb, to make kanji selection decisions for words earlier in the sentence. If you stop mid-sentence, the model must guess the kanji without the verb context, leading to significantly more homophone errors. This one habit change — finishing sentences before pausing — reduces Japanese ASR errors more than any other technique.
Related Tools
日本語で話し始めましょう — Start Dictating in Japanese
無料、インストール不要、登録不要。漢字・ひらがな・カタカナを自動出力。
今すぐ始める →Chrome推奨 — 日本語認識の精度が最も高い