Applying digital signal processing at a higher sampling rate
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**07-upsamp-processing.py**

This script demonstrates how to use pyo to apply processing on a sound
at a very high sampling rate.

Pyo offers two functions to upsample and downsample an audio file::

    upsamp(path, outfile, up, order)
    downsamp(path, outfile, down, order)

Where:

    - `path` is the path to the file to process.
    - `outfile` is the path where to save the resampled file.
    - `up`, `down` is the resampling factor (new sampling rate will be
      this value times the current sampling rate).
    - `order` is the length, in samples, of the anti-aliasing lowpass filter.

.. code-block:: python

    import os
    from pyo import *
    
    # Upsampling factor.
    SR_FACTOR = 8
    
    # Size, in samples, of the anti-aliasing lowpass filters.
    SIZE = 512
    
    # Sound to process.
    IN_SND = "../snds/baseballmajeur_m.aif"
    
    # Temporary audio files.
    UP_SND = os.path.join(os.path.expanduser("~"), "Desktop", "temp_sound_up_%i.aif" % SR_FACTOR)
    PROC_SND = os.path.join(os.path.expanduser("~"), "Desktop", "temp_sound_disto.aif")
    
    # Output sound file.
    DOWN_SND = os.path.join(os.path.expanduser("~"), "Desktop", "output_disto_down.aif")
    
    # Retrieve info about the source file.
    DUR = sndinfo(IN_SND)[1]
    SR = sndinfo(IN_SND)[2]
    
    print("Up sampling the source file %i times..." % SR_FACTOR)
    upsamp(IN_SND, UP_SND, SR_FACTOR, SIZE)
    
    print("Apply distortion at a sampling rate of %i Hz." % (SR * SR_FACTOR))
    
    # Initialize the Server in offline mode, at the desired sampling rate.
    s = Server(sr=SR * SR_FACTOR, nchnls=1, duplex=0, audio="offline").boot()
    
    # Set the recording parameters.
    s.recordOptions(dur=DUR + 0.1, filename=PROC_SND, fileformat=0, sampletype=0)
    
    # Read the upsampled version of the source file.
    sf = SfPlayer(UP_SND, loop=False, interp=4, mul=0.7)
    # Apply distortion on it.
    dist = Disto(sf, drive=0.75, slope=0.7, mul=0.3)
    # Lowpass filtering.
    filt = Biquad(dist, freq=8000, q=0.7, type=0).out()
    
    # Start the offline processing.
    s.start()
    
    print("Down sampling the processed sound %i times..." % SR_FACTOR)
    downsamp(PROC_SND, DOWN_SND, SR_FACTOR, SIZE)
    
    # Cleanup the temporary files.
    os.remove(UP_SND)
    os.remove(PROC_SND)
    
    print("Done")

