<input type="text" name="songfld[901]" value="">
<textarea name="data[901][name]" id="txt-901" rows="2" cols="80"></textarea>

<input type="text" name="songfld[902]" value="">
<textarea name="data[902][name]" id="txt-902" rows="2" cols="80"></textarea>

foreach($_POST['songfld'] as $val){
    $val is the value from input
    $id = $_POST['songfld'][0];     // the number in each name="songfld[X]"
    $namefld = $_POST['data'][$id]['name']; // gives the value from textarea

    echo "<P>$id $idfld $namefld";
}