Home Theater Forum and Systems banner

1 - 8 of 8 Posts

·
Registered
Joined
·
24 Posts
Discussion Starter · #1 ·
I plan to buy an android head unit. It's said, that these units usually have cheap components (DSP, amp) and are often cheaply build.

My equipment: Behringer ECM8000, Edirol UA 101 (USB-Audio), Laptop

I have three units to test. It seems to me from listening that they do not sound the same. One somehow sounds really bad, another maybe just not so good as my old Alpine. But what makes the sound bad? Is it flat, noisy, distorted?

To get numbers I thougt of measuring the devices with REW.
I thought of THD and linearity. And then compare it to my old Alpine.
Is there something else to measure/look at?

I also want to measure, how clean the audio player plays wav and mp3.

I have the following plan:
- play a Log-Sweep (like from this site http://www.audiocheck.net/testtones_sinesweep20-20k.php) as wav and/or mp3-file from usb-stick in the audio player of the head unit
- route it from the line output of the head unit to the audio interface
- record it as wav-file
- import it in REW using "import impulse response"

Can REW be used to measure this?
Will it give me results to judge the audio quality of the different head units?
 

·
Registered
Joined
·
106 Posts
You could indeed use REW to measure a H.U. REW can measure harmonic and intermodulation distortion, and while you won't be able to get absolute values, you can A/B compare. Mind your input and output impedance so, load your circuits properly.
 

·
Premium Member
Joined
·
6,711 Posts
Doesn't the head unit have any line inputs?

Import Impulse Response can't be used to import a sweep, sweeps and impulse responses are different things.
 

·
Registered
Joined
·
106 Posts
Doesn't the head unit have any line inputs? Import Impulse Response can't be used to import a sweep, sweeps and impulse responses are different things.
Yeah, you're right John, this is a good example of exactly what I've been trying to figure out lately. How to take a (transfer function) measurement of a SUT that does NOT have any inputs. Alot of aftermarket car audio head units THESE DAYS have aux inputs. However, not all of them do, and it's a relatively new feature. Not that many years ago it was extemely uncommon to find a H.U. with any type of input.
 

·
Registered
Joined
·
24 Posts
Discussion Starter · #5 ·
Doesn't the head unit have any line inputs?

Import Impulse Response can't be used to import a sweep, sweeps and impulse responses are different things.
Ah. Now I got it.
Anyway, the head unit has Aux in and I measured those.
However I'm looking for a way to measure or at least compare the accuracy of the audio processing.
Maybe I still can use the recorded sweeps and import them as if they where impulse responses and just compare them!?
 

·
Premium Member
Joined
·
6,711 Posts
Are you mainly interested in the audio decoding then? I suspect that usually the aux inputs would go through the same processing as anything played back locally, with the addition of the ADC.

If you import a WAV file as an impulse response REW will show the frequency response of the windowed part of it, so you could adjust the windows to get a view of the frequency content. However, only the first 256k samples are imported (about 5.5 seconds at 48 kHz). Probably better off playing the Pink PN test signal (can save a 1 minute section of that to WAV from the generator) and looking at the response on the RTA with these settings (assuming you export the 65536 sequence length PN):

 

·
Premium Member
Joined
·
6,711 Posts
No, not with the RTA, just the response shape. For distortion need to either user pure tones and the RTA for distortion at spot frequencies or run a sweep through the system via an aux input.
 
1 - 8 of 8 Posts
Top