unclear code in speech_to_text, needs a comment explaining "why" about speech-javascript-sdk HOT 6 CLOSED

I posted my own question on the DSP stack exchange to help get a better handle on this. It includes a nice graph of the filter array :)

http://dsp.stackexchange.com/questions/37450/please-help-me-understand-this-audio-downsampling-code

from speech-javascript-sdk.

nice! So you're planning to support downsampling to 8khz too? Is this to minimize bandwidth sent to watson? I'm wondering if going below 16khz actually affects recognition quality?

from speech-javascript-sdk.

Well, the service supports 8kHz "narrowband" models and 16kHz "broadband" models. Right now, when you select a narrowband model, the audio is downsampled to 16kHz here, and then I think it gets downsampled again to 8kHz at the service. So, doing it once here should both save bandwidth and increase quality.

from speech-javascript-sdk.

Ah, right I forgot about the narrowband model. So really this is about bandwidth savings when opting into the non-broadband model. Thanks for clarification.

from speech-javascript-sdk.

@nfriedly very nice!

Question about this line:

Input audio is typically 48kHz, this downsamples it to 16kHz.

I've seen several browsers provide different sample rates. For example, Chrome right now produces 44.1khz samples. I'm wondering if this filtering logic is going to slightly distort this input?

from speech-javascript-sdk.

Oh, let me adjust that. It will reduce the cutoff point of the low-pass filter slightly, but not enough to affect human speech.

from speech-javascript-sdk.