[Olympus developers 223]: Re: N-best lists for PocketSphinx / Olympus
Antoine Raux
antoine.raux at gmail.com
Tue Apr 13 13:20:12 EDT 2010
Hmmm... I don't know about word-level acoustic scores. I don't remember
ever using these. Are these actually stored in the frame that
PocketsphinxEngine and/or AudioServer send?
antoine
Thomas Harris wrote:
> Good idea. That sounds doable. But we're also not getting acoustic
> model scores. I don't know for sure, do latter stages of Olympus (like
> Helios) depend on word-level acoustic scores?
>
> -Thomas
>
> On Tue, Apr 13, 2010 at 1:12 PM, Antoine Raux <antoine.raux at gmail.com
> <mailto:antoine.raux at gmail.com>> wrote:
>
> Actually, rather than a bunch of ifs as I wrote, the (still
> temporary) solution is to get the ngram_model_t object from ps,
> and then use the sphinxbase functions (such as ngram_tg_score) to
> compute the backoff type (which is exactly what ps does at
> decoding time).
>
> antoine
>
> Thomas Harris wrote:
>
> Hi Antoine,
>
> Yes, that was/is a problem and I tried something like this.
> But even more fundamental is the problem is that the p_seg_t*
> segment iterator that you get from pocketsphinx doesn't
> correctly implement ps_seg_prob when the segment iterator
> comes from the hypothesis iterator even though it works fine
> if you get the segment iterator from the best_hyp function (or
> whatever that's called). I've sent David the code segment that
> illustrates this bug. I don't know that there's any kind of
> work around. For the most part we've gotten mutiple hypotheses
> by running multiple recognizers, I guess.
>
> Thanks,
> -Thomas
>
> On Tue, Apr 13, 2010 at 11:58 AM, Antoine Raux
> <antoine.raux at gmail.com <mailto:antoine.raux at gmail.com>
> <mailto:antoine.raux at gmail.com
> <mailto:antoine.raux at gmail.com>>> wrote:
>
> Hi all,
>
> What exactly is the confidence computation problem? Is it
> that we
> cannot compute the LM backoff type-based word confidence (see
> hyp_conf_slm in PocketsphinxEngine's main.cpp)?
> If that is the problem, one way to fix this might be to modify
> hyp_conf_slm to accept a ps_seg_t as an argument (instead of
> always getting seg_iter from ps_seg_iter):
>
> float* hyp_conf_slm (bool useFixedScore = false, ps_seg_t
> *seg_iter = NULL)
> {
> const int MAX_TYPE_SIZE = 4096;
> int32 score, type[MAX_TYPE_SIZE];
> int32 k = 0;
>
> // (antoine) no seg_iter was given, get the top segment
> iterator
> from ps
> if (seg_iter == NULL)
> seg_iter = ps_seg_iter(psd, &score);
>
> type[k++] = 3; // use the
> trigram dummy
> for first word
>
> if (seg_iter != NULL) {
> while (seg_iter = ps_seg_next(seg_iter)) {
> if (k == MAX_TYPE_SIZE) return NULL;
>
> int32 lscr, ascr;
> ps_seg_prob(seg_iter, &ascr, &lscr, &type[k++]);
> }
> }
> type[k++] = 3; // (tk) dummy trigram after utterance
> type[k++] = 3; // (tk) sometimes there's no end token, in
> which case
> // the list one was for the end token and
> this one is the dummy
>
> // (antoine) allocate the array of confidence scores
> float* conf = (float*)malloc(k*sizeof(float));
>
> for (int32 i = 1; i < k-2; i++) {
> if(!useFixedScore) {
> int32 t = type[i-1] + type[i] + ((type[i+1] +
> type[i+2])<<1); // (tk) wtf?
> conf[i-1] = (float)((double)(t-6)/12.0);
> } else {
> conf[i-1] = 0.7f;
> }
> }
>
> return conf;
> }
>
> Then further down, you can modify the third version of
> fillPartialHypStruct by just adding the argument when it calls
> hyp_conf_slm:
>
> // [2008-02-19] (antoine): this function takes a partial
> hypothesis and a reference to a
> // THypStruct and fills in the hyp
> struct
> void fillPartialHypStruct(ps_seg_t* curr_seg_iter, THypStruct*
> phs, int fromNBest) {
>
> Log(STD_STREAM, "Filling partial hyp struct\n");
>
> size_t h_len, ch_len;
> int n_words = 0, n_validwords, has_oov;
> char tmp[16384];
> float *lm_conf = NULL;
>
> // Fill in confidence values for words in result and build
> filtered hypothesis
> if (slm)
> lm_conf = hyp_conf_slm(curr_seg_iter);
> else
> lm_conf = hyp_conf_slm(curr_seg_iter, true);
>
> (...)
>
> I don't really have any setup to test this but if someone
> who has
> could give it a shot and post the result to the mailing list...
> Now it might be that I misunderstood what the problem was
> altogether (in which case I apologize for the spam)...
>
> On a side note, the big commented out block in
> getHypStructs (as
> sent by Blaise) is from my Cactus code (which I had sent to
> Blaise
> as an example), so it's irrelevant to Olympus and should be
> deleted (for clarity's sake).
>
> antoine
>
> Blaise Thomson wrote:
>
> Hi Thomas / Alan,
>
> I've now got some preliminary N-best list code to work with
> PocketSphinx. With the help of some example code from
> Antoine
> I've modified the pocketsphinx engine to produce a
> 1-best list
> for partial recognition results but an N-best list upon
> completion. I've also modified the AudioServer to be
> able to
> receive multiple N-best lists from each of the
> recognizer (the
> number for each decoder specified by an optional ":N" after
> the decoder definition in the config file). In case
> this may
> be something you want to include in future versions of
> Olympus
> I've attached my modified files.
>
> Note, however, that the code still doesn't produce any
> confidence score information for the N-best list. For this
> reason we will still probably be unable to use Olympus
> for our
> version of the LetsGo! system. If the PocketSphinx bugs you
> mentioned are fixed any time soon or if anyone finds
> out how
> to get confidence scores with the N-best list would you
> please
> let us know?
>
> Many thanks,
> Blaise
>
>
>
> Thomas Harris wrote:
>
> Hi Blaise,
>
> Thanks for looking into this. I hope we can include
> your
> bugfixes. I've been looking into this as well, and
> there's
> a more fundamental issue. It seems like you can't
> get word
> confidence metrics from the PocketSphinx segment
> iterators
> when you've gotten the sement iterators from the n_best
> hypothisis iterator. It smells like a PocketSphinx bug,
> but I haven't seen any reference implementation of
> PocketSphinx that makes use of those confidence
> metrics in
> an n_best setting, so I'm not sure that it isn't a
> problem
> with how the PocketSphinx api is used. Until that
> issue is
> resolved n_best lists won't work in Olympus, too many
> downhill processes depend on those confidence metrics.
>
> Thanks,
> -Thomas
>
> On Wed, Mar 24, 2010 at 4:39 AM, Blaise Thomson
> <brmt2 at cam.ac.uk <mailto:brmt2 at cam.ac.uk>
> <mailto:brmt2 at cam.ac.uk <mailto:brmt2 at cam.ac.uk>>
> <mailto:brmt2 at cam.ac.uk <mailto:brmt2 at cam.ac.uk>
> <mailto:brmt2 at cam.ac.uk <mailto:brmt2 at cam.ac.uk>>>> wrote:
>
> Dear Olympus developers,
>
> I am trying to get the Olympus LetsGo! system to
> provide an N-best
> list of speech recognition hypotheses. I found the
> -n_best switch
> which can be passed to the PocketSphinxEngine
> which is
> supposed to
> enable this but when I set the switch to
> anything other
> than 0 the
> system crashes immediately on any audio input. I
> remember you said
> that the system had been build to provide N-best
> lists
> so I was
> wondering if you could give any advice on why it
> is not
> working.
> Do you have a working N-best list system that
> you could
> send me to
> see how things are configured?
>
> In trying to solve the problem I took a look at the
> PocketSphinxEngine source code and have noticed some
> possible
> memory access bugs which may be contributing to
> this.
> These were
> related to the way the iHypsGenerated variable was
> used. I've
> fixed these and can send them if you would like (I
> tried attaching
> them but the mailing list won't let me). The
> resulting
> code still
> crashes but at a later stage. After the fix, the
> log file
> generates a WARNING: "ngram_search.c", line 1000:. I
> don't know if
> this might be the cause of the problem. There is
> also a
> possibility that I simply have to add a
> configuration
> variable to
> PocketSphinx itself. At the moment I have only
> used the
> n_best
> switch on PocketSphinxEngine.
>
> Please do let me know if you have any ideas of
> how to
> get this
> working or who else to contact.
>
> Thanks for all you help,
>
> Blaise
>
>
>
>
>
>
>
>
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