Pronunciation audio enhancement

#!/usr/bin/env bash

# Gets the path to an audio file provided as the first parameter. Resamples the
# audio to 44100 Hertz, turns stereo into mono, boosts frequences above 6
# kilohertz, normalizes to 0dBFS, strips silence and pads with 100 milliseconds
# of silence at the beginning and at the end of the audio. The supported audio
# formats are WAV, MP3, OGG.

####### Functions #######

function is_installed()
{
    # Check if required apps are installed.
    local app_name="$1"

    if command -v "$app_name" > /dev/null; then
        return 0
    else
        return 1
    fi
}

function announce()
{
    # Make announcements with espeak or echo if espeak is not installed.
    local message="$1"

    if is_installed "espeak"; then
        espeak -v "whisper" -s 300 "$message"
    else
        echo "$message"
    fi
}

function leave()
{
    # Make the final announcement and exit with a specified exit status.
    local message="$1"
    local exit_status="$2"

    announce "$message"
    exit "$exit_status"
}

####### Main #######

if ! is_installed "sox"; then
    leave "SOX is not installed!" 1
fi

temp_file=$(mktemp --suffix='.wav')

target_file="$1"

if ! [ -f "$target_file" ]; then
    leave "The target file doesn't exist anymore!" 1
fi

mime_type=$(file --mime-type -b "$target_file")

if [[ $mime_type != audio/mpeg && $mime_type != audio/ogg && $mime_type != audio/x-wav && $mime_type != audio/wav ]]; then
    leave "Not MP3, WAV or OGG" 1
fi

# Disable dithering because it may cause clipping, resample, convert to mono,
# make headroom, amplify higher frequencies, normalize to 0 dBFS, remove
# silence from the beginning and the end of the audio, pad the audio at the
# end and at the beginning with silent segments 0.1 second long.
sox "$target_file" -D -r 44100 -c 1 "$temp_file" norm -6 treble +6 6k norm silence 1 0.1 -40d reverse silence 1 0.1 -40d reverse pad 0.1 0.1
sox "$temp_file" "$target_file" || leave "Couldn't reverse-convert the audio!" 1
play "$target_file"

# Mark the target audio file with a "check" ("tick") icon and timestamp the
# file to make sure the icon appears without making the file manager refresh.
if is_installed "gio"; then
    gio set "$target_file" -t stringv metadata::emblems emblem-default
    touch "$target_file"
else
    announce "Gio is not installed! Can't mark the processed file!"
fi