Working with an array from VKontakte api, how to get photo and audio?

Question

PHP

Hello.
Guys, tell me, please, how to work with an array that gives VKontakte when requested.
I make a request

$result = json_decode(file_get_contents('https://api.vk.com/method/wall.getById?'. $get_params));

To get the first value of the array, I do like this.
$result -> response[0] -> text;
But if I need to get a photo or audio attachment to a post from the wall (which is the method I use), I don't know how to get to it.
Tried like this

$result -> response[0] -> copy_history[0] -> attachments[0] -> photo;

That doesn't work.
I tried to parse with regular expressions, but writes NULL
I do var_dump($result);
I get the following array.
Tell me how to get to the photo and audio ??

object(stdClass)#1 (1) {
  ["response"]=> 
  array(1) {
    [0]=>
    object(stdClass)#2 (10) {
      ["id"]=>
      int(3804)
      ["from_id"]=>
      int(90161593)
      ["owner_id"]=>
      int(90161593)
      ["date"]=>
      int(1469004331)
      ["post_type"]=>
      string(4) "post"
      ["text"]=>
      string(0) ""
      ["copy_history"]=>
      array(1) {
        [0]=>
        object(stdClass)#3 (8) {
          ["id"]=>
          int(110778)
          ["owner_id"]=>
          int(-46347604)
          ["from_id"]=>
          int(-46347604)
          ["date"]=>
          int(1468999805)
          ["post_type"]=>
          string(4) "post"
          ["text"]=>
          string(665) "Аудиокнига «Психология влияния» - Р.Чалдини

"В этой книге Роберт Чалдини, доктор наук, профессор психологии и признанный эксперт в сфере влияния и убеждения, рассматривает шесть универсальных приемов, благодаря которым вы станете настоящим мастером уговоров. В то же время, зная об этих приемах, вы всегда сможете избежать нежелательного воздействия со стороны.""
          ["attachments"]=>
          array(10) {
            [0]=>
            object(stdClass)#4 (2) {
              ["type"]=>
              string(5) "photo"
              ["photo"]=>
              object(stdClass)#5 (13) {
                ["id"]=>
                int(422898685)
                ["album_id"]=>
                int(-7)
                ["owner_id"]=>
                int(-46347604)
                ["user_id"]=>
                int(100)
                ["photo_75"]=>
                string(50) "http://cs7002.vk.me/v7002028/1f8f9/Q5Ky-U5eWa0.jpg"
                ["photo_130"]=>
                string(50) "http://cs7002.vk.me/v7002028/1f8fa/_ch9S6xrr9g.jpg"
                ["photo_604"]=>
                string(50) "http://cs7002.vk.me/v7002028/1f8fb/WtioodnFjZ8.jpg"
                ["width"]=>
                int(470)
                ["height"]=>
                int(600)
                ["text"]=>
                string(0) ""
                ["date"]=>
                int(1468999804)
                ["post_id"]=>
                int(110778)
                ["access_key"]=>
                string(18) "18a1e10557a69906af"
              }
            }
            [1]=>
            object(stdClass)#6 (2) {
              ["type"]=>
              string(5) "audio"
              ["audio"]=>
              object(stdClass)#7 (8) {
                ["id"]=>
                int(382665174)
                ["owner_id"]=>
                int(2000148619)
                ["artist"]=>
                string(65) "Роберт Чалдини - Психология влияния"
                ["title"]=>
                string(41) "Глава 1. Орудия влияния"
                ["duration"]=>
                int(4002)
                ["date"]=>
                int(1437303323)
                ["url"]=>
                string(183) "http://cs1-37v4.vk-cdn.net/p9/973e9bb850388d.mp3?extra=3FVfPJqxC7efhviZGhUEpVdbetHgkCHgANU6-vCeClHiVWYP9u4wwWCccrJfTwoi6FsaOQ1e287nZ4m2ofXkmM-qjyrEvmUhh0Yp_57UY_UJeuoF-kngyoYGXQTTX7ME"
                ["album_id"]=>
                int(2)
              }
            }
            [2]=>
            object(stdClass)#8 (2) {
              ["type"]=>
              string(5) "audio"
              ["audio"]=>
              object(stdClass)#9 (8) {
                ["id"]=>
                int(456239453)
                ["owner_id"]=>
                int(2000372708)
                ["artist"]=>
                string(66) "Роберт Чалдини - Психология  влияния"
                ["title"]=>
                string(30) "2. Взаимный обмен"
                ["duration"]=>
                int(4848)
                ["date"]=>
                int(1468999805)
                ["url"]=>
                string(183) "http://cs1-50v4.vk-cdn.net/p6/6b106b730523ce.mp3?extra=M1e_R9FgA3bN0_V5GCCuLtN7GQS9mABv-xvXYje1VKKzgn0bI1bHVPl6BFqQqyexKtJoJq8PnyZmaM0A8oMVOG0iTD6mBg69ASziYzkwpnFCtF3qcA0PJ1TN4XkBPjW5"
                ["genre_id"]=>
                int(1001)
              }
            }
            [3]=>
            object(stdClass)#10 (2) {
              ["type"]=>
              string(5) "audio"
              ["audio"]=>
              object(stdClass)#11 (8) {
                ["id"]=>
                int(456239452)
                ["owner_id"]=>
                int(2000372827)
                ["artist"]=>
                string(66) "Роберт Чалдини - Психология  влияния"
                ["title"]=>
                string(71) "3. Обязательство и последовательность-1"
                ["duration"]=>
                int(4849)
                ["date"]=>
                int(1468999805)
                ["url"]=>
                

тут я обрезал, одно и  тоже



      }
    }
  }
}

Answer 1

Add ->photo_604 . Variants of numbers corresponding to the size of the photo are in the documentation. With the comparison of numbers, I think you can handle it.

Answer 2

Fixed
$result->response[0]->copy_history[0]->attachments[0]->photo->photo_604
$result->response[0]->copy_history[0]->attachments[1]->audio ->url