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MiniAmp audio quality

Tomasz Kasprzak

May 08, 2019 17:17

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Hello,

I'm using HiFiBerry miniamp and RPI 3A+ in my audio project. Unfortunately, I can hear sound distortion during playback. I've checked it with few different pairs of speakers.

I was trying to measure it. So I started to play 1kHz sine at -20dB and connected miniamp output to PC sound card line input (it's Asus Xonar). I'm pretty sure card input is not overdriven.

I've attached screenshot from REW RTA window. It seems there is some serious problems with the sound quality. Probably I'm doing something wrong or maybe my miniamp module is defective?

I would be grateful for any advices.

Some additional info:

- I'm using the latest Raspbian

- I'm using alsa, always 48000Hz

- I've disabled HDMI and USB

- Wifi and Bluetooth are enabled

- I have the original Raspberry power supply.

 

I've also checked "noise floor", when there is no playback. It doesn't look so bad.

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5 comments

• 0
  
  andre October 13, 2019 16:08

  I’d also be interested to see an answer to this question. I’m generally surprised at the lack of measurements provided for these products. I know some audio companies don’t provide measurements because they are concerned their users won’t understand them, but in this case, I think the user audience is very experienced and can appreciate the nuances of FFTs.

• 0
  
  HiFiBerry team October 14, 2019 11:58

  You can't measure this with a sound card. The MiniAmp uses a floating Class-D output that is not compatible with a ground-based sound card input. This will generate all kinds of distortions. You can be happy that you didn't damage your sound card input. You will need an audio analyser with a brick filter and floating input to make useful measurements of the MiniAmp or the Amp2. 

  The MiniAmp might not be powerful enough for your project. If you bought it directly from us and you're not happy with the audio quality, you can return it. If you think, it might be defective, we can test it here. 

  @Andre: Some companies provide single number of THD+N or similar. That doesn't makes sense at all in our opinion as there is no "single number". There also isn't a singe FFT that tells you everything about sound quality. So we would have to create lots of different measurements (as distortions vary with a lot of different parameters). We think, the best is to to listen to the card. If you buy a card from us and you're not happy with the sound quality, you can return it within 4 weeks:

  https://www.hifiberry.com/shop/money-back-guarantee/ 

• 0
  
  Tomasz Kasprzak October 15, 2019 20:15

  It's true that my measurements were not accurate (I was also using wrong window function, now I know that). But I think it cannot measure well because distortion is quite noticeable to my ear.

  I also think HiFiBerry should publish measurements. Of course "single number" is not very useful but THD+N/Power and THD+N/Frequency graphs would be great value.

  Anyway, I've bought similar amp from other firm. It sound good IMO and measures much better (using my inaccurate method).

   

• 0
  
  HiFiBerry team October 16, 2019 05:02

  Your measurements were not incorrect because of a wrong window function, but because you're using a ground-based sound card input. To do measurements like this you need an audio analyzer with floating inputs and correct filtering. If you want to send the MiniAmp to us, we can check it here. If it really is defective, we'll replace it.

  Best regards,
  Daniel

• 0
  
  andre October 16, 2019 05:19

  I never claimed a single FFT would fully characterize the performance of an amplifier, but you could effectively profile it’s performance in a few charts. That you share nothing because a single number can’t capture everything strikes me as odd. Companies like Hypex, Allo, and ICEpower all provide these measurements in an easily digestible form.