android中的撥号鍵盤音也是可以改變的，不過不同的是，按鍵音并不是存儲在手機中的ogg格式的音頻檔案。他是通過C++代碼中的頻率設定來實作的。
具體的音頻控制在frameworks/av/media/libmedia檔案夾中的ToneGenerator.cpp中實作：
const ToneGenerator::ToneDescriptor ToneGenerator::sToneDescriptors[] = {
{ segments: {{ duration: ToneGenerator::TONEGEN_INF, waveFreq: { 1336, 941, 0 }, 0, 0},
{ duration: 0 , waveFreq: { 0 }, 0, 0}},
repeatCnt: ToneGenerator::TONEGEN_INF,
repeatSegment: 0 }, // TONE_DTMF_0
{ segments: { { duration: ToneGenerator::TONEGEN_INF, waveFreq: { 1209, 697, 0 }, 0, 0 },
{ duration: 0 , waveFreq: { 0 }, 0, 0}},
repeatCnt: ToneGenerator::TONEGEN_INF,
repeatSegment: 0 }, // TONE_DTMF_1
{ segments: { { duration: ToneGenerator::TONEGEN_INF, waveFreq: { 1336, 697, 0 }, 0, 0 },
{ duration: 0 , waveFreq: { 0 }, 0, 0}},
repeatCnt: ToneGenerator::TONEGEN_INF,
repeatSegment: 0 }, // TONE_DTMF_2
{ segments: { { duration: ToneGenerator::TONEGEN_INF, waveFreq: { 1477, 697, 0 }, 0, 0 },
{ duration: 0 , waveFreq: { 0 }, 0, 0}},
repeatCnt: ToneGenerator::TONEGEN_INF,
repeatSegment: 0 }, // TONE_DTMF_3
我隻截取了0-3号鍵盤的音頻生成代碼，其中的函數功能在ToneGenerator.h中有詳細說明：
- The array waveFreq[]:
// 1 for static tone descriptors: contains the frequencies of all individual waves making the multi-tone.
// 2 for active tone descritors: contains the indexes of the WaveGenerator objects in mWaveGens
// The number of sine waves varies from 1 to TONEGEN_MAX_WAVES.
// The first null value indicates that no more waves are needed.
// - The array segments[] is used to generate the tone pulses. A segment is a period of time
// during which the tone is ON or OFF. Segments with even index (starting from 0)
// correspond to tone ON state and segments with odd index to OFF state.
// The data stored in segments[] is the duration of the corresponding period in ms.
// The first segment encountered with a 0 duration indicates that no more segment follows.
// - loopCnt - Number of times to repeat a sequence of seqments after playing this
// - loopIndx - The segment index to go back and play is loopcnt > 0
// - repeatCnt indicates the number of times the sequence described by segments[] array must be repeated.
// When the tone generator encounters the first 0 duration segment, it will compare repeatCnt to mCurCount.
// If mCurCount > repeatCnt, the tone is stopped automatically. Otherwise, tone sequence will be
// restarted from segment repeatSegment.
// - repeatSegment number of the first repeated segment when repeatCnt is not null
本來想做成鋼琴音的效果，但是對于頻率波神馬的無能為力。。。随意改動出來的效果實在難聽。。。就放棄了。