My project

I realise this thread hasn't been open in months, but I thought I'd post the resolution to my issues here, for anyone looking to do a similar project in the future. Code is as follow:

// include SPI, MP3, Servo and SD libraries
#include <SPI.h>             // We will use the hardware SPI pins: CLK (13), MISO (12), MOSI (11)
#include "Adafruit_VS1053.h"
#include <SD.h>
int track1, track2, track3;
const int pingPin = 8;
const int echoPin = 9;
unsigned int duration, inches;


// These are the pins used for the music maker shield
#define SHIELD_RESET  -1      // VS1053 reset pin (unused!)
#define SHIELD_CS      7      // VS1053 chip select pin (output)
#define SHIELD_DCS     6      // VS1053 Data/command select pin (output)

// These are common pins between breakout and shield
#define CARDCS 4     // Card chip select pin
// DREQ should be an Int pin, see http://arduino.cc/en/Reference/attachInterrupt
#define DREQ 3       // VS1053 Data request, ideally an Interrupt pin

Adafruit_VS1053_FilePlayer musicPlayer = 
 
  Adafruit_VS1053_FilePlayer(SHIELD_RESET, SHIELD_CS, SHIELD_DCS, DREQ, CARDCS);

  void setup() {
  
  track1=0;
  track2=0;
  track3=0;
  pinMode(8,OUTPUT);
  pinMode(9,INPUT);
  Serial.begin(9600);
  Serial.println("File From Distance Test");

  if (! musicPlayer.begin()) { // initialise the music player
     Serial.println(F("Couldn't find VS1053, do you have the right pins defined?"));
     while (1);
  }
  Serial.println(F("VS1053 found"));
  
  SD.begin(CARDCS);    // initialise the SD card
  
  // Set volume for left, right channels. lower numbers == louder volume!
  musicPlayer.setVolume(5,5);
  }

void ping()  {
  digitalWrite(pingPin, LOW);        // Ensure pin is low
  delayMicroseconds(2);
  digitalWrite(pingPin, HIGH);       // Start ranging
  delayMicroseconds(5);              //   with 5 microsecond burst
  digitalWrite(pingPin, LOW);        // End ranging
 
  duration = pulseIn(echoPin, HIGH); // Read echo pulse
  inches = duration / 74 / 2;        // Convert to inches
  Serial.println(inches);            // Display result
  if ((inches>3) && (inches<7)) { Serial.println("1"); delay(1000); }
  if ((inches>8) && (inches<12))  { Serial.printIn("2"); delay(1000); }
  if ((inches>13) && (inches<17))  { Serial.printIn("3"); delay(1000( ;}
  
}
void loop() {
  delay(50);
  ping();
   if ((inches>3) && (inches<7)) {
    if (track1==0){
    musicPlayer.playFullFile("track001.mp3");
    track1=1; track2=0; track3=0;}
   }
  
   
   if ((inches>8) && (inches<12)) {
   if (track2==0){
   musicPlayer.playFullFile("track002.mp3");
    track2=1; track1=0; track3=0;
    } //track2=0
   } //inches

   if ((inches>13) && (inches<17)) {
    if (track3==0){

   musicPlayer.playFullFile("track003.mp3");} 
   track3=1; track2=0; track1=0;}
}

Uses the library for the Music Maker shield, and a couple of others, and uses if statements, combined with distance readouts to control the (currently 3) files stored on the microSD. There's also a line UNDER each if statement that acts as a flag, to stop monotonous replaying of the same note, so that one note cannot be triggered a second time, until another one has been activated first.

Anyway, thanks for your help a few months ago, only have a week till hand in now!! I'll be increasing the amount of files controlled by this code to 7 or 8 tomorrow, and then hopefully EITHER including another sensor to max out the pin usage of my Uno, or I'll be resoldering everything to a Mega and trying to incorporate 5 sensors. All depends on time now, I'll post up the finished code as well when it's done.

Thanks again, Regards.