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我正在尝试使用该Data.WAVE库在 Haskell 中以编程方式从格式为“Note Octave Note Octave”（例如 A 4 F# 1）的文件生成 .wav 文件，但我遇到了一个问题：我无法弄清楚如何准确计算要存储的内容作为注释。到目前为止，我正在尝试将它们存储为根据八度音阶音符的频率计算得出的正弦波，但我从扬声器中得到的只是咔嗒声。我做错了什么，这没有产生音调？

import Data.WAVE
import Graphics.UI.SDL.Mixer.Samples

import Control.Applicative
import Data.List.Split (splitOn)
import Data.Char
import Data.Int (Int32)
import Data.List (group)
import System.IO (hGetContents, Handle, openFile, IOMode(..))

a4 = 440.0

frameRate = 16000

noteToFreq :: (String, Int) -> Double
noteToFreq (note, octave) =
    if octave >= -1 && octave < 10
    then if n /= 15.0
         then (2 ** (n + (12.0 * ((fromIntegral octave ::Double) - 4.0)))) * a4
         else error $ "Bad note: " ++ note
    else error $ "Bad octave: " ++ show octave
    where n = case note of
                "B#" -> -9.0
                "C"  -> -9.0
                "C#" -> -8.0
                "Db" -> -8.0
                "D"  -> -7.0
                "D#" -> -6.0
                "Eb" -> -6.0
                "E"  -> -5.0
                "Fb" -> -5.0
                "E#" -> -4.0
                "F"  -> -4.0
                "F#" -> -3.0
                "Gb" -> -3.0
                "G"  -> -2.0
                "G#" -> -1.0
                "Ab" -> -1.0
                "A"  -> 0.0
                "A#" -> 1.0
                "Bb" -> 1.0
                "B"  -> 2.0
                "Cb" -> 2.0
                _    -> 15.0

notesToSamples :: [(String, Int)] -> [WAVESample]
notesToSamples ns =
    map doubleToSample [sin $ pi * i * (f/fr) | i <- [0,0.1..len], f <- freqs]
    where freqs = map noteToFreq ns
          fr = fromIntegral frameRate :: Double
          len = fromIntegral (length ns) :: Double

getFileName :: IO FilePath
getFileName = putStr "Enter the name of the file: " >> getLine

openMFile :: IO Handle
openMFile = getFileName >>= \path -> 
            openFile path ReadMode

getNotesAndOctaves :: IO String
getNotesAndOctaves = openMFile >>= hGetContents

noteValuePairs :: String -> [(String, Int)]
noteValuePairs = pair . splitOn " "
    where pair (x:y:ys) = (x, read y) : pair ys
          pair []       = []

getWavSamples :: IO [WAVESample]
getWavSamples = (notesToSamples . noteValuePairs) <$> getNotesAndOctaves 

constructWAVE :: IO WAVE
constructWAVE = do
  samples <- map (:[]) . concatMap (replicate 1000) <$> getWavSamples
  let channels      = 1
      bitsPerSample = 32
      frames        = Just (length samples)
      header        =
          WAVEHeader channels frameRate bitsPerSample frames
  return $ WAVE header samples

makeWavFile :: IO ()
makeWavFile = constructWAVE >>= \wav -> putWAVEFile "temp.wav" wav
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1 回答 1

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这是一些使用该库生成音调的代码，您应该希望能够使用该代码来解决您自己的问题。首先检查它是否为给定的输入产生了正确的频率——我从未测试过。我实际上并没有检查您的代码，因为大多数与声音生成无关。对于这类问题，我通常会尝试编写最简单的代码来让外部库正常工作，然后再围绕它编写自己的抽象：

module Sound where
import Data.WAVE
import Data.Int (Int32)
import Data.List.Split (splitOn)

samplesPS = 16000
bitrate = 32

header = WAVEHeader 1 samplesPS bitrate Nothing

sound :: Double  -- | Frequency
      -> Int -- | Samples per second
      -> Double -- | Lenght of sound in seconds
      -> Int32 -- | Volume, (maxBound :: Int32) for highest, 0 for lowest
      -> [Int32]
sound freq samples len volume = take (round $ len * (fromIntegral samples)) $ 
                         map (round . (* fromIntegral volume)) $
                         map sin [0.0, (freq * 2 * pi / (fromIntegral samples))..]

samples :: [[Int32]]
samples = map (:[]) $ sound 600 samplesPS 3 (maxBound `div` 2)

samples2 :: [[Int32]] -- play two tones at once
samples2 = map (:[]) $ zipWith (+) (sound 600 samplesPS 3 (maxBound `div` 2)) (sound 1000 samplesPS 3 (maxBound `div` 2))

waveData = WAVE header samples


makeWavFile :: WAVE -> IO ()
makeWavFile wav = putWAVEFile "temp.wav" wav

main = makeWavFile waveData

一旦你开始工作，你就可以围绕它写一个更好的抽象。您应该能够为这个库获得一个很好的纯抽象，因为唯一使用 IO 的函数是将其写入文件的函数。

于 2011-04-14T06:14:07.443 回答