Waveform analysis/Top and tail

Waveform analysis/Top and tail is a draft programming task. It is not yet considered ready to be promoted as a complete task, for reasons that should be found in its talk page.

The task is to crop a given audio waveform file, removing any leading or trailing silence from the wave file, leaving just the audible sound.

The task should utilize a configurable audio squelch level calibration parameter that enables the user to set the silence level threshold (enabling low level background hiss or hum to be removed from the leading and trailing edges of the audio file.)

Moments of silence (below the squelch threshold), should be removed from the leading and trailing edges of the input wave file, to produce a new cleanly cropped audio file.

Note that the output file format should be the same as the initial input format. This should not be changed by the implemented procedure.

Go

As Go does not have any audio support in its standard library, this invokes the SoX utility to trim any leading or trailing silence from an audio file.

Unfortunately, you must know the length of the silence at the end of the audio file to trim off silence reliably. To work around this, we first trim off leading silence from the file, reverse it and then trim off the leading silence from that file. We then reverse the resulting file to the output file specified by the user.

Setting the squelch level to 2 or 3 per cent of the maximum sample value worked reasonably well in my tests. <lang go>package main

import (

   "bufio"
   "fmt"
   "log"
   "os"
   "os/exec"
   "strconv"

)

func check(err error) {

   if err != nil {
       log.Fatal(err)
   }

}

func main() {

   const sec = "00:00:01"
   scanner := bufio.NewScanner(os.Stdin)
   name := ""
   for name == "" {
       fmt.Print("Enter name of audio file to be trimmed : ")
       scanner.Scan()
       name = scanner.Text()
       check(scanner.Err())
   }

   name2 := ""
   for name2 == "" {
       fmt.Print("Enter name of output file              : ")
       scanner.Scan()
       name2 = scanner.Text()
       check(scanner.Err())
   }    
   
   squelch := 0.0
   for squelch < 1 || squelch > 10 {
       fmt.Print("Enter squelch level % max (1 to 10)    : ")
       scanner.Scan()
       input := scanner.Text()
       check(scanner.Err())
       squelch, _ = strconv.ParseFloat(input, 64)
   }
   squelchS := strconv.FormatFloat(squelch, 'f', -1, 64) + "%"

   tmp1 := "tmp1_" + name
   tmp2 := "tmp2_" + name

   // Trim audio below squelch level from start and output to tmp1.
   args := []string{name, tmp1, "silence", "1", sec, squelchS}
   cmd := exec.Command("sox", args...)
   err := cmd.Run()
   check(err) 

   // Reverse tmp1 to tmp2.
   args = []string{tmp1, tmp2, "reverse"}     
   cmd = exec.Command("sox", args...)
   err = cmd.Run()
   check(err)

   // Trim audio below squelch level from tmp2 and output to tmp1.  
   args = []string{tmp2, tmp1, "silence", "1", sec, squelchS}
   cmd  = exec.Command("sox", args...)
   err = cmd.Run()
   check(err)

   // Reverse tmp1 to the output file.
   args = []string{tmp1, name2, "reverse"}    
   cmd = exec.Command("sox", args...)
   err = cmd.Run()
   check(err)

   // Remove the temporary files.
   err = os.Remove(tmp1)
   check(err)
   err = os.Remove(tmp2)
   check(err)

}</lang>

Julia

Implemented as a Gtk GUI app. <lang julia>using FileIO, Gtk, LibSndFile, Printf

function dB(buf, i, channels, cutoff=0.001)

   xsum = sum(buf[k, j] * buf[k, j] for j in 1:channels, k in i-1:i+1)
   sigmean = xsum / (channels * 3)
   return sigmean < cutoff ? -60.0 : 20 * log(10, sigmean)

end

function silencecropperapp()

   win = GtkWindow("Sound File Silence Cropping Tool", 800, 200) |> (GtkFrame() |> (vbox = GtkBox(:v)))
   infilename, outfilename, modifyinputfile, trimmable = "", "", false, true
   outchoices = Vector{GtkRadioButton}(undef, 2)
   outchoices[1] = GtkRadioButton("Crop the Input File In-Place", active=true)
   outchoices[2] = GtkRadioButton(outchoices[1], "Copy Output to File Chosen Below")
   inbutton = GtkButton("Click to Choose Input File")

   senslabel = GtkLabel("Threshold (db)")
   thresholdslider = GtkScale(false, -40.0:10.0)
   adj = GtkAdjustment(thresholdslider)
   push!(vbox, outchoices[1], outchoices[2], inbutton, senslabel, thresholdslider)

   crop = Vector{GtkRadioButton}(undef, 3)
   crop[1] = GtkRadioButton("Crop File at Beginning")
   crop[2] = GtkRadioButton(crop[1], "Crop File at End")
   crop[3] = GtkRadioButton(crop[2], "Crop Both Ends", active=true)
   cropchoice() = [get_gtk_property(b, :active, Bool) for b in crop]

   trimfilebutton = GtkButton("Trim!")
   push!(vbox, crop[1], crop[2], crop[3], trimfilebutton)

   hbox = GtkBox(:h)
   textentry = GtkEntry()
   set_gtk_property!(textentry, :expand, true)
   set_gtk_property!(textentry, :text, "Set Output File")
   pickoutfilebutton = GtkButton("Choose Existing File for Output")
   push!(hbox, textentry, pickoutfilebutton)
   push!(vbox, hbox)
   
   function reinitialize()
       infilename, outfilename, modifyinputfile, trimmable = "", "", true, true
       set_gtk_property!(trimfilebutton, :label, "Trim!")
       toggleoutputactive(win)
   end
   function toggleoutputactive(w)
       if get_gtk_property(outchoices[2], :active, Bool)
           set_gtk_property!(textentry, :editable, true)
           set_gtk_property!(textentry, :text, "Set Output File")
           modifyinputfile = false
       elseif get_gtk_property(outchoices[1], :active, Bool)
           set_gtk_property!(textentry, :editable, false)
           set_gtk_property!(textentry, :text, "Set Output File")
           outfilename = ""
           modifyinputfile = true
       end
   end
   function pickinput(w)
       filename = open_dialog("Pick a sound or music file to be trimmed.")
       if filesize(filename) > 0
           infilename = filename
           set_gtk_property!(inbutton, :label, infilename)
       end
       trimbuttonlabel(win)
   end
   function pickoutput(w)
       if get_gtk_property(outchoices[2], :active, Bool)
           outfilename = open_dialog("Pick Output File To Be Overwritten.")
           set_gtk_property!(textentry, :text, outfilename)
           show(textentry)
       end
   end
   function trimbuttonlabel(w)
       tstart, tend, tboth = cropchoice()
       toggleoutputactive(win)
       if filesize(infilename) > 0
           scut, ecut, b, nframes, fs = getsilence(get_gtk_property(adj, :value, Float64))
           if (tboth && scut <= 1 && ecut >= nframes) ||
               (tstart && scut <= 1) || (tend && ecut >= nframes)
               set_gtk_property!(trimfilebutton, :label, "Nothing to trim.")
               trimmable = false
           else
               text = @sprintf("Trim %7.2f seconds at front and %7.2f seconds at back.",
                   (scut - 1) / fs, (nframes - ecut) / fs)
               set_gtk_property!(trimfilebutton, :label, text)
               trimmable = true
           end
       else
           set_gtk_property!(trimfilebutton, :label, "Trim!")
       end
   end
   function trimsilence(w)
       if trimmable
           if modifyinputfile
               outfilename = infilename
           elseif outfilename == ""
               s = get_gtk_property(textentry, :text, String)
               outfilename = s != "Set Output File" ? s :
                   open_dialog("Pick or enter a file for output")
           end
           if filesize(outfilename) <= 0 || ask_dialog("Really change file $infilename?")
               scut, ecut, buf, n, fs = getsilence(get_gtk_property(adj, :value, Float64))
               FileIO.save(outfilename, buf[scut:ecut, :])
               info_dialog("File $outfilename saved: $(filesize(outfilename)) bytes.", win)
               reinitialize()
           end
       end
   end
   function getsilence(threshold, granularity=0.1)
       buf = load(infilename)
       (buflen, channels) = size(buf)
       startcut, endcut = 0, buflen
       nframes = LibSndFile.nframes(buf)
       fs = LibSndFile.samplerate(buf)
       cchoices = cropchoice()
       if cchoices[1] || cchoices[3]
           pos = findfirst(i -> dB(buf, i, channels) > threshold, 2:buflen-1)
           if pos == nothing
               # all below threshold
               return buflen, 0, buf, nframes, fs
           else
               startcut = Int(floor(((pos / fs) - (pos / fs) % granularity) * fs))
               startcut = startcut < 1 ? 1 : startcut
           end
       end
       if cchoices[2] || cchoices[3]
           pos = findlast(i -> dB(buf, i, channels) > threshold, 2:buflen-1)
           if pos != nothing
               endcut = Int(ceil((granularity + (pos / fs) - (pos / fs) % granularity) * fs))
               endcut = endcut > nframes ? nframes : endcut
           end
       end
       return startcut, endcut, buf, nframes, fs
   end

   foreach(i -> signal_connect(toggleoutputactive, outchoices[i], :clicked), 1:2)
   foreach(i -> signal_connect(trimbuttonlabel, crop[i], :clicked), 1:3)
   signal_connect(pickoutput, pickoutfilebutton, :clicked)
   setfromtext(w) = (outfilename = get_gtk_property(textentry, :text, String))
   signal_connect(pickinput, inbutton, :clicked)
   signal_connect(trimsilence, trimfilebutton, :clicked)
   toggleoutputactive(win)

   cond = Condition()
   endit(w) = notify(cond)
   signal_connect(endit, win, :destroy)
   showall(win)
   wait(cond)

end

silencecropperapp() </lang>

Nim

Translation of: Go

<lang Nim>import os, osproc, strutils

const Sec = "00:00:01"

proc getString(prompt: string): string =

 while true:
   stdout.write prompt
   stdout.flushFile()
   try:
     result = stdin.readLine().strip()
     if result.len != 0: break
   except EOFError:
     quit "\nEOF encountered. Quitting.", QuitFailure

proc getFloatValue(prompt: string; minval, maxval: float): float =

 while true:
   stdout.write prompt
   stdout.flushFile()
   try:
     result = stdin.readLine.strip().parseFloat()
     if result notin minval..maxval:
       echo "Invalid value"
     else:
       return
   except ValueError:
     echo "Error: invalid value."
   except EOFError:
     quit "\nEOF encountered. Quitting.", QuitFailure

let infile = getString("Enter name of audio file to be trimmed: ") let outfile = getString("Enter name of output file: ") let squelch = getFloatValue("Enter squelch level % max (1 to 10): ", 1, 10) let squelchS = squelch.formatFloat(ffDecimal, precision = -1) & '%'

let tmp1 = "tmp1_" & infile let tmp2 = "tmp2_" & infile

1. Trim audio below squelch level from start and output to tmp1.

var args = @[infile, tmp1, "silence", "1", Sec, squelchS] discard execProcess("sox", args = args, options = {poStdErrToStdOut, poUsePath})

1. Reverse tmp1 to tmp2.

args = @[tmp1, tmp2, "reverse"] discard execProcess("sox", args = args, options = {poStdErrToStdOut, poUsePath})

1. Trim audio below squelch level from tmp2 and output to tmp1.

args = @[tmp2, tmp1, "silence", "1", Sec, squelchS] discard execProcess("sox", args = args, options = {poStdErrToStdOut, poUsePath})

1. Reverse tmp1 to the output file.

args = @[tmp1, outfile, "reverse"] discard execProcess("sox", args = args, options = {poStdErrToStdOut, poUsePath})

1. Remove the temporary files.

removeFile(tmp1) removeFile(tmp2)</lang>

Phix

The first part is a copy of Musical_scale#version_2 but with first and last 2s written out as silence.
I referred to http://soundfile.sapp.org/doc/WaveFormat/ when writing this.
You may want to check for average volume over some period, rather than just all-0.
This is clearly just a starting point and not a practical/useful/finished product! <lang Phix>constant sample_rate = 44100,

        duration = 8,
        dataLength = sample_rate * duration,
        hdrSize = 44,
        fileLen = dataLength + hdrSize - 8,
        freqs = { 261.6, 293.6, 329.6, 349.2, 392.0, 440.0, 493.9, 523.3 },
        wavhdr = "RIFF"&
                 int_to_bytes(fileLen,4)&
                 "WAVE"&
                 "fmt "&
                 int_to_bytes(16,4)&           -- length of format data (= 16)
                 int_to_bytes(1,2)&            -- type of format (= 1 (PCM))
                 int_to_bytes(1,2)&            -- number of channels (= 1)
                 int_to_bytes(sample_rate,4)&  -- sample rate
                 int_to_bytes(sample_rate,4)&  -- sample rate * bps(8) * channels(1) / 8 (= sample rate)
                 int_to_bytes(1,2)&            -- bps(8) * channels(1) / 8  (= 1)
                 int_to_bytes(8,2)&            -- bits per sample (bps) (= 8)
                 "data"&               
                 int_to_bytes(dataLength,4)    -- size of data section
       if length(wavhdr)!=hdrSize then ?9/0 end if -- sanity check

integer fn = open("notes.wav", "wb") puts(fn, wavhdr) for j=1 to duration do

   atom omega = 2 * PI * freqs[j]
   for i=0 to dataLength/duration-1 do
       atom y = 32 * sin(omega * i / sample_rate)

-- integer byte = and_bits(y,#FF) -- (makes for no cropping)

       integer byte = iff(j<=2 or j>=7?0:and_bits(y,#FF))
       puts(fn,byte)
   end for

end for close(fn) -- </copy of Musical_scale>

string raw = get_text("notes.wav") if raw[1..4]!="RIFF" then ?9/0 end if integer rawlen = bytes_to_int(raw[5..8]) if rawlen!=fileLen then ?9/0 end if if raw[9..12]!="WAVE" then ?9/0 end if if raw[13..16]!="fmt " then ?9/0 end if if bytes_to_int(raw[17..20])!=16 then ?9/0 end if -- 2 bytes per sample if bytes_to_int(raw[21..22])!=1 then ?9/0 end if -- must be PCM integer channels = bytes_to_int(raw[23..24]) if channels!=1 and channels!=2 then ?9/0 end if -- mono or stereo (else??) integer bps = bytes_to_int(raw[35..36]) if bps!=8 and bps!=16 then ?9/0 end if -- 8 or 16 bits per sample? bps = bps/8*channels*2 -- ===> bytes per sample (pair(s)(s)) if raw[37..40]!="data" then ?9/0 end if integer rawdata = bytes_to_int(raw[41..44]) if rawdata!=dataLength then ?9/0 end if integer bs, be, crop = 0 for bs=45 to length(raw) by bps do

   -- some volume threshold...
   if sum(raw[bs..bs+bps-1])>0 then exit end if -- (assumes unsigned)
   crop += bps

end for for be = length(raw) to bs by -bps do

   if sum(raw[be-bps+1..be])>0 then exit end if
   crop += bps

end for if crop=0 then

   printf(1,"nothing to crop\n")

else

   printf(1,"cropping %d bytes\n",crop)
   rawlen -= crop
   rawdata -= crop
   raw[5..8] = int_to_bytes(rawlen,4)
   raw[41..44] = int_to_bytes(rawdata,4)
   raw = raw[1..be]
   raw[46..bs-1] = {}
   fn = open("notes.wav","wb")
   puts(fn,raw)
   close(fn)

end if

-- without cropping 8s, with 4s if platform()=WINDOWS then

   system("notes.wav")

elsif platform()=LINUX then

   system("aplay notes.wav")

end if</lang>

Wren

Translation of: Go

The ability to call external processes such as SoX is expected to be added to Wren-cli in the next release. In the meantime, we embed the following Wren script in a C host to complete this task. <lang ecmascript>/* waveform_analysis_top_and_tail.wren */

class C {

   foreign static getInput(maxSize)

   foreign static sox(args)

   foreign static removeFile(name)

}

var sec = "00:00:01"

var name = "" while (name == "") {

   System.write("Enter name of audio file to be trimmed : ")
   name = C.getInput(80)

}

var name2 = "" while (name2 == "") {

   System.write("Enter name of output file              : ")
   name2 = C.getInput(80)

}

var squelch = 0 while (!squelch || squelch < 1 || squelch > 10) {

   System.write("Enter squelch level \% max (1 to 10)    : ")
   squelch = Num.fromString(C.getInput(5))

} var squelchS = squelch.toString + "\%"

var tmp1 = "tmp1_" + name var tmp2 = "tmp2_" + name

// Trim audio below squelch level from start and output to tmp1. var args = [name, tmp1, "silence", "1", sec, squelchS] C.sox(args.join(" "))

// Reverse tmp1 to tmp2. args = [tmp1, tmp2, "reverse"] C.sox(args.join(" "))

// Trim audio below squelch level from tmp2 and output to tmp1. args = [tmp2, tmp1, "silence", "1", sec, squelchS] C.sox(args.join(" "))

// Reverse tmp1 to the output file. args = [tmp1, name2, "reverse"] C.sox(args.join(" "))

// Remove the temporary files. C.removeFile(tmp1) C.removeFile(tmp2)</lang>
We now embed this in the following C program, compile and run it. <lang c>#include <stdio.h>

1. include <stdio_ext.h>
2. include <stdlib.h>
3. include <string.h>
4. include "wren.h"

void C_getInput(WrenVM* vm) {

   int maxSize = (int)wrenGetSlotDouble(vm, 1) + 2;
   char input[maxSize];
   fgets(input, maxSize, stdin);
   __fpurge(stdin);
   input[strcspn(input, "\n")] = 0;
   wrenSetSlotString(vm, 0, (const char*)input);

}

void C_sox(WrenVM* vm) {

   const char *args = wrenGetSlotString(vm, 1);
   char command[strlen(args) + 4];
   strcpy(command, "sox ");
   strcat(command, args);
   system(command);

}

void C_removeFile(WrenVM* vm) {

   const char *name = wrenGetSlotString(vm, 1);
   if (remove(name) != 0) perror("Error deleting file.");

}

WrenForeignMethodFn bindForeignMethod(

   WrenVM* vm,
   const char* module,
   const char* className,
   bool isStatic,
   const char* signature) {
   if (strcmp(module, "main") == 0) {
       if (strcmp(className, "C") == 0) {
           if (isStatic && strcmp(signature, "getInput(_)") == 0)   return C_getInput;
           if (isStatic && strcmp(signature, "sox(_)") == 0)        return C_sox;
           if (isStatic && strcmp(signature, "removeFile(_)") == 0) return C_removeFile;
       }
   }
   return NULL;

}

static void writeFn(WrenVM* vm, const char* text) {

   printf("%s", text);

}

void errorFn(WrenVM* vm, WrenErrorType errorType, const char* module, const int line, const char* msg) {

   switch (errorType) {
       case WREN_ERROR_COMPILE:
           printf("[%s line %d] [Error] %s\n", module, line, msg);
           break;
       case WREN_ERROR_STACK_TRACE:
           printf("[%s line %d] in %s\n", module, line, msg);
           break;
       case WREN_ERROR_RUNTIME:
           printf("[Runtime Error] %s\n", msg);
           break;
   }

}

char *readFile(const char *fileName) {

   FILE *f = fopen(fileName, "r");
   fseek(f, 0, SEEK_END);
   long fsize = ftell(f);
   rewind(f);
   char *script = malloc(fsize + 1);
   fread(script, 1, fsize, f);
   fclose(f);
   script[fsize] = 0;
   return script;

}

int main(int argc, char **argv) {

   WrenConfiguration config;
   wrenInitConfiguration(&config);
   config.writeFn = &writeFn;
   config.errorFn = &errorFn;
   config.bindForeignMethodFn = &bindForeignMethod;
   WrenVM* vm = wrenNewVM(&config);
   const char* module = "main";
   const char* fileName = "waveform_analysis_top_and_tail.wren";
   char *script = readFile(fileName);
   WrenInterpretResult result = wrenInterpret(vm, module, script);
   switch (result) {
       case WREN_RESULT_COMPILE_ERROR:
           printf("Compile Error!\n");
           break;
       case WREN_RESULT_RUNTIME_ERROR:
           printf("Runtime Error!\n");
           break;
       case WREN_RESULT_SUCCESS:
           break;
   }
   wrenFreeVM(vm);
   free(script);
   return 0;

}</lang>