hiss on audio expander cape

Fedde

Hi guys,

possibly I'm missing out on something. I was testing the audio expander cape on all channels with a test tone. An unacceptable high hiss is there on the channels that come from the expander cape. When listening to the first two that come from the Bela cape directly there is a relative clear sound.

Thanks for any clarification.

giuliomoro

Were you using heavy for this? If yes, then try again with the code I fixed last night and it should work better. However, the audio quality of the expander is never going to be close to the audio outputs.
More details are here, http://blog.bela.io/2016/11/07/bela-analogue-vs-audio/ , however the take home message is that you will get more distortion, aliasing and noise than with the regular audio outputs. A sine tone is a particularly unforgiving example: having some more complex signal going through that will make the artefacts less unpleasant and more bearable, however do not expect to obtain a hi-fi output.

Fedde

giuliomoro Thank you. Thought so. I haven't tried it with heavy yet. thx

Bulien

I just spent the whole afternoon trying to get rid of the hiss on the audio expander outputs, then I found this thread and read this sentence:

However, the audio quality of the expander is never going to be close to the audio outputs.

@giuliomoro I think it would be worth stating this as clearly in the audio expander product description, to set expectations straight. I didn't understand this as clearly when I hit the purchase button.

giuliomoro

Hi,
thanks for your feedback.

The product description mentions:

(For an in-depth look at turning analog inputs into audio channels, how it works and what it means, see our Audio vs Analog post.)

, where the linked article explains all in detail. We thought that the article is as transparent as we could get, by listing all the pros and cons. However, perhaps that's TOO MUCH detail, and it is not so immediately helpful. We shall add something more meaningful to the product description to avoid confusion in the future.

Bulien

Yes maybe that's too much detail! Maybe a couple audio files could help get a better sense of what these number mean in the end.
Don't get me wrong I love Bela and still support it though!
One side question then: do the CTAG products suffer the same way, or can I expect the same audio quality on all outputs?

giuliomoro

Those are Sigma-delta converters, so they are properly designed for audio, with even better SNR than Bela's codec. Specs here.