[Docs] Fix Speech Encoder Decoder doc sample (#18346)

* [Docs] Fix Speech Encoder Decoder doc sample

* improve pre-processing comment

* make style

docs/source/en/model_doc/speech-encoder-decoder.mdx

@@ -85,25 +85,26 @@ As you can see, only 2 inputs are required for the model in order to compute a l
 speech inputs) and `labels` (which are the `input_ids` of the encoded target sequence).
 
 ```python
->>> from transformers import Wav2Vec2Processor, SpeechEncoderDecoderModel
+>>> from transformers import AutoTokenizer, AutoFeatureExtractor, SpeechEncoderDecoderModel
 >>> from datasets import load_dataset
 
->>> processor = Wav2Vec2Processor.from_pretrained("facebook/wav2vec2-base-960h")
->>> tokenizer = BertTokenizer.from_pretrained("bert-base-uncased")
->>> model = SpeechEncoderDecoderModel.from_encoder_decoder_pretrained(
-...     "facebook/wav2vec2-base-960h", "bert-base-uncased"
-... )
+>>> encoder_id = "facebook/wav2vec2-base-960h"  # acoustic model encoder
+>>> decoder_id = "bert-base-uncased"  # text decoder
 
->>> model.config.decoder_start_token_id = processor.tokenizer.cls_token_id
->>> model.config.pad_token_id = processor.tokenizer.pad_token_id
+>>> feature_extractor = AutoFeatureExtractor.from_pretrained(encoder_id)
+>>> tokenizer = AutoTokenizer.from_pretrained(decoder_id)
+>>> # Combine pre-trained encoder and pre-trained decoder to form a Seq2Seq model
+>>> model = SpeechEncoderDecoderModel.from_encoder_decoder_pretrained(encoder_id, decoder_id)
 
->>> # load a speech input
+>>> model.config.decoder_start_token_id = tokenizer.cls_token_id
+>>> model.config.pad_token_id = tokenizer.pad_token_id
+
+>>> # load an audio input and pre-process (normalise mean/std to 0/1)
 >>> ds = load_dataset("hf-internal-testing/librispeech_asr_dummy", "clean", split="validation")
->>> input_values = processor(ds[0]["audio"]["array"], return_tensors="pt").input_values
+>>> input_values = feature_extractor(ds[0]["audio"]["array"], return_tensors="pt").input_values
 
->>> # load its corresponding transcription
->>> with processor.as_target_processor():
-...     labels = processor(ds[0]["text"], return_tensors="pt").input_ids
+>>> # load its corresponding transcription and tokenize to generate labels
+>>> labels = tokenizer(ds[0]["text"], return_tensors="pt").input_ids
 
 >>> # the forward function automatically creates the correct decoder_input_ids
 >>> loss = model(input_values, labels=labels).loss