[Speex-dev] iPhone distorted audio

Thomas Leavy tom at the-all-nighters.com
Sat Jul 14 21:33:31 PDT 2012

I'm not sure if anyone is experienced with this but i'm having very strange issues with implementing speex in my iOS application. 

I have written a encode and decode function basically exactly like the example files online. To process audio I am using an iOS VoiceProcessingIO Audio Unit which is set at 16bit pcm with 8000 sample rate. After buffering 320 bytes of PCM audio I feed it into my encode function set at quality 10 (comes out to about 62 bytes of compressed audio). Then after sending it across the net I buffer 62 byte chunks and feed them into the decode function for playback. Unfortunately playback is strange as it sounds very distorted and robotic, although I can clearly recognize what was said and the encode and decode functions go through without any errors. I bypassed the speex functions and just sent uncompressed PCM using the same app and its crystal clear. Where am I going wrong here? Anyone got any suggestions?

My code is as follows

#define AUDIO_QUALITY 10
#define FRAME_SIZE 160
#define COMP_FRAME_SIZE 62

char *encodeSpeexWithBuffer(spx_int16_t *buffer, int *insize) {
    SpeexBits bits;
    void *enc_state;
    char *outputBuffer = (char *)malloc(COMP_FRAME_SIZE);
    enc_state = speex_encoder_init(&speex_nb_mode);
    int quality = AUDIO_QUALITY;
    speex_encoder_ctl(enc_state, SPEEX_SET_QUALITY, &quality);
    speex_encode_int(enc_state, buffer, &bits);

    *insize = speex_bits_write(&bits, outputBuffer, COMP_FRAME_SIZE);
    return outputBuffer;

short *decodeSpeexWithBuffer(char *buffer) {
    SpeexBits bits;
    void *dec_state;
    dec_state = speex_decoder_init(&speex_nb_mode);
    short *outTemp = (short *)malloc(FRAME_SIZE * 2);

    speex_bits_read_from(&bits, buffer, COMP_FRAME_SIZE);
    speex_decode_int(dec_state, &bits, outTemp);
    return outTemp;

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