pvsbufread
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## pvsbufread

pvsbufread — This opcode reads a circular buffer of f-signals (streaming PV signals).

## Description

This opcode reads from a circular buffer of length ilen (secs), taking a handle for the buffer and a time pointer, which holds the current read position (also in seconds). It is used in conjunction with a pvsbuffer opocde. Reading is circular, wrapping around at the end of the buffer.

## Syntax

    fsig pvsbufread  ktime, khandle[, ilo, ihi, iclear]

## Initialisation

ilo, ihi -- set the lowest and highest freqs to be read from the buffer (defaults to 0, Nyquist).

iclear -- set to 1 to clear output fsig before every write (default 1), 0 tells the opcode not to clear the output fsig. This is relevant when writing to subsets of an fsig frame using ilo, ihi.

## Performance

fsig -- output pv stream

ktime -- time position of reading pointer (in secs).

khandle -- handle identifying the buffer to be read. When using k-rate handles, it is important to initialise the k-rate variable to a given existing handle. When changing buffers, fsig buffers need to be compatible (same fsig format).

With this opcode and pvsbuffer, it is possible to, among other things:

- time-stretch/compress a fsig stream, by reading it at different rates
- delay a fsig or portions of it.
- 'brassage' two or more fsigs by switching buffers, since the reading handles are k-rate. Note that, when using k-rate handles, it is important to initialise the k-rate variable to a given handle (so that the fsig initialisation can take place) and it is only possible to switch handles between compatible fsig buffers (with the same fftsize and overlap).

| Note
It is important that the handle value passed to pvsbufread is valid and was created by pvsbuffer. Csound will crash with invalid handles.

## Examples

Here is an example of the pvsbufread opcode. It does 'brassage' by switching between two buffers.

Example 634. Example of the pvsbufread opcode

See the sections Real-time Audio and Command Line Flags for more information on using command line flags.

    fsig1       pvsanal     asig1, 1024, 256, 1024, 1
    fsig2       pvsanal     asig2, 1024, 256, 1024, 1

    ibuf1, kt1  pvsbuffer   fsig1, 10   ; 10-sec buf with fsig1
    ibuf2, kt2  pvsbuffer   fsig2, 7    ; 7-sec buf with fsig2

    khan        init        ibuf1       ; initialise handle to buf1

    if  ktrig  > 0 then                 ; switch buffers according to trigger
    khan = ibuf2
    else
    khan = ibuf1
    endif

    fsb         pvsbufread  kt1, khan   ; read buffer

Here is an example of the pvsbufread opcode. It uses the file pvsbufread.csd.

Example 635. Example of the pvsbufread opcode.

See the sections Real-time Audio and Command Line Flags for more information on using command line flags.

    <CsoundSynthesizer>
    <CsOptions>
    ; Select audio/midi flags here according to platform
    ; Audio out   Audio in
    -odac    ;;;RT audio I/O
    ; For Non-realtime ouput leave only the line below:
    ; -o pvsbufread.wav -W ;;; for file output any platform
    </CsOptions>
    <CsInstruments>

    sr = 44100
    ksmps = 16
    nchnls = 1
    0dbfs = 1

    ;; example written by joachim heintz 2009

    opcode FileToPvsBuf, iik, Siiii
    ;;writes an audio file at the first k-cycle to a fft-buffer (via pvsbuffer)
    Sfile, ifftsize, ioverlap, iwinsize, iwinshape xin
    ktimek		timeinstk
    if ktimek == 1 then
    ilen		filelen	Sfile
    kcycles	=		ilen * kr; number of k-cycles to write the fft-buffer
    kcount		init		0
    loop:
    ain		soundin	Sfile
    fftin		pvsanal	ain, ifftsize, ioverlap, iwinsize, iwinshape
    ibuf, ktim	pvsbuffer	fftin, ilen + (ifftsize / sr)
    		loop_lt	kcount, 1, kcycles, loop
    		xout		ibuf, ilen, ktim
    endif
    endop

    instr 1
    ifftsize	=		1024
    ioverlap	=		ifftsize / 4
    iwinsize	=		ifftsize
    iwinshape	=		1; von-Hann window
    ibuffer, ilen, k0		FileToPvsBuf	"fox.wav", ifftsize, ioverlap, iwinsize, iwinshape
    ktmpnt		linseg		ilen, p3, 0; reads the buffer backwards in p3 seconds
    fread 		pvsbufread  	ktmpnt, ibuffer
    aout		pvsynth	fread
    		out		aout
    endin

    </CsInstruments>
    <CsScore>
    i 1 0 5
    e
    </CsScore>
    </CsoundSynthesizer>

## See Also

pvsanal, pvsynth, pvsbuffer, pvsadsyn

## Credits

Author: Victor Lazzarini
July 2007

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