Problem using AudioSource.timeSamples

I'm trying to sync game events to audio beats, and I'm trying to use AudioSource.timeSamples

I've got a test scene, with a single game object which has an audio source, and the following behaviour:

 public class AudioTest : MonoBehaviour 
 {
     private int m_LastSample;
     
     // Use this for initialization
     void Start () 
     {
         m_LastSample = 0;
     }
     
     // Update is called once per frame
     void Update () 
     {
         AudioSource audio = GetComponent<AudioSource>();
         
         float freq = (float)audio.clip.frequency;
         int sample = audio.timeSamples;
         int sampleDelta = sample - m_LastSample;
         if (sampleDelta < 0)
             sampleDelta += audio.clip.samples;
         
         float delta = (float)sampleDelta / freq;
         
         print (string.Format("Freq={0} Curr={1} Last={2} Delta={3} Time.deltaTime={4}", freq, sample, m_LastSample, delta, Time.deltaTime));
         
         m_LastSample = sample;
     }
 }

The output I get from this is:

Freq=44100 Curr=43008 Last=41984 Delta=0.02321995 Time.deltaTime=0.01595402

Freq=44100 Curr=43008 Last=43008 Delta=0 Time.deltaTime=0.01716399

Freq=44100 Curr=44032 Last=43008 Delta=0.02321995 Time.deltaTime=0.01597601

Freq=44100 Curr=45056 Last=44032 Delta=0.02321995 Time.deltaTime=0.01675498

which is to me unexpected because

a) the sample position doesn't appear to be updated every frame and b) the time delta that I calculate is somewhat larger than Time.deltaTime

Can I not use AudioSource.timeSamples in this way?

The behaviour I'm after is to eg. spawn something at point A sync'd with audio, and then have the object move to point B sync'd to another beat. The audio I'm using for the test is a short, looped sample that only contains 4 beats, hence the test for wraparound.