| Write data to .WAV file? [message #10689] |
Thu, 15 January 1998 00:00  |
lauth
Messages: 1
Registered: January 1998
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Junior Member |
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Hello all
Does anyone have an IDL routine which
writes an array of data into a .WAV file?
Regards,
Uwe
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| Re: Write data to .WAV file? [message #10764 is a reply to message #10689] |
Mon, 19 January 1998 00:00  |
hahn
Messages: 108
Registered: November 1993
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Senior Member |
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lauth@linmpi.mpg.de_spamstop (Uwe Lauth) wrote:
> Hello all
>
> Does anyone have an IDL routine which writes an array of data into a .WAV file?
>
> Regards,
> Uwe
RIFF wav files are a bit trickly to handle because they are organized in chunks
and the sequence of the chunks are not fixed. If you restrict yourself to
process the data chunk only and assume that it is the first chunk after the
header processing is fairly easy.
To process a RIFF WAV file, you open the file in IDL and read the header.
Here is a data structure I use to read and write uncompressed .wav files:
WAV_HDR = { WAVE_HEADER, $
ID1:'****', LoF:0L, ID2:'********', LoH:0L, $
FMT:0, NChan:0, SpSc:0L, DpSc:0L, $
BypSa:0, BipSa:0, ID3:'****', LoD:0L }
; ID1 the letters "RIFF"
; LOF bytes from here (i.e. from byte 8) to end of file
; ID2 the letters "WAVE" followed by "fmt "
; "fmt " is the beginning of the format descriptor block
; LoH Length of Header (here 16 Bytes format descriptor) that follows
; ---- start of format header ----
; FMT format tag, 1 = PCM, 101 = ADPCM
; NChan channels (1 = Mono, 2 = Stereo ...)
; SpSc samples per second
; DpSc data bytes per second = samples per second * bytes per sample
; BypSa bytes per sample = channels * (bits per sample / 8)
; BipSa bits per sample
; ---- end of format header ----
; Now watch for "data": Other blocks will be skipped.
; ID3 the letters "data". This is the beginning of the data block
; LoD data length, i.e. the number of bytes of the actual data.
; ---- start of sampled data ----
; for multi-channel samples 1st byte is channel 1, 2nd byte is
; channel 2, 3rd byte channel 3 (or if 2 channels, channel 1 again)
; Amplitude (y-values) from -127 to 127 or -32767 to 32767.
; ---- end of sampled data ----
; Other chunks may follow. Don't play 'em
;
Now pick those attribute you may need to know, i.e. sample rate, number
of bits per sample, and use this information to allocate byte arrays or integer
arrays. Then go on and read the data. All is done in binary. Note that the byte
order is Intel (least significant byte first).
Here comes a piece of IDL code to perform a consistency check on the header.
It forces a sampling rate of 48,000 sampes/sec, 16 bit per sample and 2
channels.
pro repwav, dsn, sps = sps
;
; Prozedur zum Reparieren des Kopfes einer Wave-Datei. Der Parameter sps
; gibt die Samplingrate an. Default ist 48000.
; Der Parameter dsn ist der Dateiname. Wenn nicht angegeben, wird
; Pickfile aufgerufen.
;
@c:\musik\wavhdr.inc
if n_elements(sps) eq 0 then new_sps = 48000 else new_sps = sps
if dsn eq '?' then $
in_dsn = Pickfile ( Path = 'd:\musik\data', Filter = '*.wav' ) $
else $
in_dsn = dsn
If In_dsn eq '' Then Return
In_hdr = { Wave_Header } ; Kopf der Eingabe-Datei deklarieren
In_hdr = Wav_HDR ; und initialisieren.
; Datei oeffnen, den Kopf lesen und auf dem Bildschirm anzeigen.
OpenU, iunit, In_dsn, /get_lun
In_dcb = fstat ( iunit )
ReadU, iunit, In_hdr
print, In_hdr
; Alle Elemente des Wave-Headers auf Plausibilit�t pr�fen.
In_hdr.id1 = 'RIFF'
In_hdr.id2 = 'WAVEfmt '
In_hdr.id3 = 'data'
if In_hdr.LoF ne ( In_dcb.size - 8 ) then $
In_hdr.LoF = In_dcb.size - 8
In_hdr.LoH = 16
In_hdr.fmt = 1
In_hdr.NChan = 2
In_hdr.SpSC = new_sps
In_hdr.BipSa = 16
In_hdr.BypSa = In_hdr.NChan * In_hdr.BipSa / 8
In_hdr.DpSC = In_hdr.spsc * In_hdr.bypsa
In_hdr.LoD = In_hdr.LoF - In_hdr.LoH - 20
ReadU, iunit, ampl16
help, In_hdr, /stru
; plot, ampl16
Point_Lun, iunit, 0
WriteU, iunit, In_HDR
; Datei schliessen, Kanal freigeben
free_lun, iunit
dsn = in_dsn
end
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