I've been following the process of using LPC to analyse the speech and then synthesize the speech by swapping out coefficients over time. I'm purely concerned with pitched vowels at this point.
lpc(speech_segment)
gives us $a_{p}$ coefficients of an IIR filter, where $p$ is the order. This IIR filter has the frequency response of the speech vowel/formant present in speech_segment
.
I have a pulse train to use as a source
.
I see two ideologies for synthesis:
some texts talk about using the IIR filter to filter the
source
, which makes sense to me intuitively - juxtaposing the vowel's frequency response to my source's spectrumOther texts talk about using the inverse of this IIR filter to form an FIR, and then filter the source somehow. I think I understand why this is invertible and stable (minimum-phase).
So approach 2 makes less sense to me from source-filter perspective, but it would be really useful because it means I can perform LPC analysis-synthesis with OLA convolution of audio blocks rather than implement the filter recursively.
Is my understanding of either of these two approaches, not quite right? If not, what exactly changes to make each possible.