speex_encode_int performance iphone4 + iOS5

Hi,I'm having performance issues encoding with speex on an iphone4 + iOS5. The same code yields excellent results on iPad2 + iOS5, Mac OS X 10.6 as well as Windows 7. The call to speex_encode_int is takes 0.0065 to complete. Because encoding is so latent the receiver incurs underruns.
Here is my speex setup:
    unsigned val = 0;
    /**     * Initialize the encoder in narrow band mode.     */    encoder_state_ = speex_encoder_init(speex_lib_get_mode(SPEEX_MODEID_NB));     /**     * A quality of ...     */    val = 7;        /**     * Set the quality.     */    speex_encoder_ctl(encoder_state_, SPEEX_SET_QUALITY, &val);        /**     * A complexity of ...     */    val = 0;        /**     * Set the complexity.     */    speex_encoder_ctl(encoder_state_, SPEEX_SET_COMPLEXITY, &val);
    /**     * A bit rate of 8000     */    val = default_sample_rate;        /**     * Set the bit rate.     */    speex_encoder_ctl(encoder_state_, SPEEX_SET_BITRATE, &val);        /**     * Disable vad.     */    val = 0;        /**     * Disable vad.     */    speex_encoder_ctl(encoder_state_, SPEEX_SET_VAD, &val);        /**     * Disable dtx.     */    val = 0;        /**     * Disable dtx.     */    speex_encoder_ctl(encoder_state_, SPEEX_SET_DTX, &val);        /**     * Disable vbr.     */    val = 0;        /**     * Disable vbr.     */    speex_encoder_ctl(encoder_state_, SPEEX_SET_VBR, &val);
Here is the time elapsed on iphone4:Encoding took 0.006500 seconds.Encoding took 0.004000 seconds.
And on Mac OS X:Encoding took 0.000805 seconds.Encoding took 0.000792 seconds.
Thanks in advance!