Headphone vs HDMI audio

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Has anybody noticed a material difference in audio quality between
the headphone jack and what comes out of the HDMI port?  

Obviously, a display with a poor audio circuit can corrupt a good
signal, but assuming the display is "good enough" does it matter
which is used?

Thanks for reading,

bob prohaska




Re: Headphone vs HDMI audio
bob prohaska wrote:
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It has been discussed such as here  
https://raspberrypi.stackexchange.com/questions/47699/sound-output-of-the-raspberry-pi


(that also has a number of useful links)

The problem is the limitations of how RPi generates the analog audio --  
'tacky' for an audiophile.

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Someone suggested that if you want really good audio, to use a card for  
the GPIO header:  
https://elinux.org/index.php?title=RPi_Expansion_Boards#Sound

RPi Expansion Boards
2.10 Sound

     2.10.1 Audio Injector zero sound card
     2.10.2 Audio Injector stereo sound card
     2.10.3 Audio Injector Octo sound card
     2.10.4 Wolfson sound card
     2.10.5 HiFiBerry DAC
     2.10.6 HiFiBerry Digi
     2.10.7 Raspi-T-DAC
     2.10.8 Pisound


--  
Mike Easter

Re: Headphone vs HDMI audio
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The GPIO header allows connection to the PCM audio output signals.
These are the digital signals used to generate the analogue audio at
the headphone jack using a DAC (apparantly a very cheap
implementation using PWM according to the Stack Exchange link).

A quick look on Wikipedia indicates that HDMI also carries PCM audio,
so in theory HDMI audio should be equally good as the audio from the
GPIO because they're actually the same data (ignoring optional
formats over HDMI which might be slightly better in some specific
respects than the PCM - no idea if the Pi supports any of those, or
how they're any better for that matter).

https://en.wikipedia.org/wiki/HDMI

USB sound cards probably use PCM as well, though I don't know if the
bitrate limits might be lower, and some apparantly introduce a
delay. As far as quality goes it's most likely to be the DAC that
really counts, and anything sold as an audio adapter should be better
than PWM unless it's a complete rip-off.

--  
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#_ < |\| |< _#

Re: Headphone vs HDMI audio
Computer Nerd Kev wrote:

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When I started to employ my 3B RPi using some leftover parts, I had a  
VGA monitor and USB kb & mouse, so I needed an HDMI to VGA adapter.  
There were places that had adapters w/ a 3.5mm for audio, but I opted  
for an adapter w/o audio plug outlet in favor of just using the RPi's  
audio outs for some little 'computer speakers'.

But, I'm puzzled about the analog vs digital.  I would assume that the  
HDMI audio is digital, but the 3.5mm plug sounds/looks like an analog  
audio outlet.

But, I'm sure those HDMI to VGA adapters w/ audio plug aren't converting  
digital to analog audio.  What is the answer to my confusion?


--  
Mike Easter

Re: Headphone vs HDMI audio
On 23/08/2019 00:45, Mike Easter wrote:
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Why not?
To do it rather badly is not that hard


--  
If you tell a lie big enough and keep repeating it, people will  
eventually come to believe it. The lie can be maintained only for such  
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Re: Headphone vs HDMI audio
On Thu, 22 Aug 2019 16:45:46 -0700, Mike Easter wrote:

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ng  
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Just got a cheap HDMI to VGA adapter with audio from CPC:

AV27363 - UNBRANDED 77HDMIVGCBL033 HDMI to VGA Lead with Audio, Gold

  
As HDMI has no analog audio it must be converting the HDMI digital
audio stream to stereo analog on its 3.5 mm jack plug. Not sure if it
or omxplayer on a Raspberry Pi is doing a basic 5.1 or 7.1 mix down
to stereo. All I know is that if I play a channel check video file
with only a 5.1 or 7.1 sound track I do hear all the channels on the
correct side (and center) and at various levels. Except the .1 (LFE)
which is to be expected.

Quality is pretty good, the level might be a bit on the high side.

--  
Cheers
Dave.




Re: Headphone vs HDMI audio
On Fri, 23 Aug 2019 10:06:41 +0100 (BST), "Dave Liquorice"

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https://www.cablestogo.com/product/40714/pro-hdmi-to-vga-and-audio-adapter-converter
indicates that the adapter converts both video and audio to analog

    But one should still need an amplifier for the audio output as that is
most likely (consumer) line-level.


--  
    Wulfraed                 Dennis Lee Bieber         AF6VN
     snipped-for-privacy@ix.netcom.com    http://wlfraed.microdiversity.freeddns.org/

Re: Headphone vs HDMI audio
Dennis Lee Bieber wrote:
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But that is a $67 box.  The adapters I saw w/ or w/o audio out were  
comparable in price; $10 w/o audio  
https://www.amazon.com/Cable-Matters-Adapter-Converter-Black/dp/B00879DM56;  


$13 w/ audio  
https://www.walmart.com/ip/Cable-Matters-Active-HDMI-to-VGA-Adapter-with-Audio-Support-in-Black/49419838?athcpid49%419838&athpgid=athenaItemPage&athcgid=null&athznid=PWVUB&athieid=v0&athstid=CS004&athguid62%4b10de-da1-16cbf2d04fdb56&athena=true

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The $13 Walmart w/ audio also comes w/:  Audio Output: 3.5mm stereo jack  
with included stereo cable (6')

When I refer to 'little computer speakers' they are powered and line out  
(like RPi), not headphone jacked.


--  
Mike Easter

Re: Headphone vs HDMI audio
Mike Easter wrote:
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So, those economical adapters have sufficient circuitry inside to do the  
DAC for the audio and video.

I was curious about how much +5V HDMI current was available for that  
circuitry and found this thread in the RPi section of stackexchange:

https://raspberrypi.stackexchange.com/questions/45001/how-much-current-can-i-draw-from-each-models-hdmi-socket
  How much current can I draw from each model's HDMI socket?


--  
Mike Easter

Re: Headphone vs HDMI audio
On Fri, 23 Aug 2019 13:56:46 -0700, Mike Easter wrote:

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$10  
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I expect there is just a single, SOC type, chip that does the lot and
it's up to the adapater maker to decide what features are made
available to the user. Remember that there is more to such an adapter
than just the DAC. Each end of the HDMI talk to each other to find
the "best" resolution and bit rates they have in common.

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That was a slight concern for the one I bought but it works fine
connected to Pi3B+.

--  
Cheers
Dave.




Re: Headphone vs HDMI audio
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Bluetooth speakers may be another option for Pis with wireless. These
again receive digital audio and have built-in DACs.

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It is.


It is.


They are actually, and VGA video is analogue as well, which is
actually a much bigger ask. All the devices probably use a similar
chip which has been developed to integrate the whole functionality
into one $0.40 lump which just needs to be soldered onto a circuit
board with a few other parts like the plugs and sockets. Quite
possibly the cheap devices (maybe the expensive ones too) use chips
from some unheard-of Chinese company that doesn't care about quality
but sells them cheap enough to put in a $10 adapter. The few
additional components like filter capacitors could also have been
stuffed up, causing noise to be introduced to the analogue audio
output. All the same, the chip itself most likely uses a real DAC
which is better quality than that used for the onboard analogue
audio from the Pi, and so in theory the result should be better
quality.

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For better audio you want a well designed DAC. It can connect to GPIO,
HDMI, or bluetooth, all equally effective at conveying the same
digital audio signal from the Pi.

What you get with the onboard analogue audio output on the Pi is a
cheaply designed (for probably justified reasons) DAC which also uses
the same digital audio data, but produces analogue audio using a
function of the SoC hardware that was not designed to be used as an
audio DAC. As such the results are not optimal.

--  
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#_ < |\| |< _#

Re: Headphone vs HDMI audio
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IIUC, the transition from digital to analog audio then occurs in the
monitor, if using the HDMI connection, or the Pi itself, if using the
headphone jack. Have I got this much right?

I've tried using the audio output on a Dell ST2200L HDMI monitor and the
headphone jack, neither showed any obvious defects.  

Thanks to all for reading and posting informative links.....

bob prohaska
  
test  

Re: Headphone vs HDMI audio
On 23/08/2019 03:09, bob prohaska wrote:
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No, the defects are subtle.
But they are there


--  
If you tell a lie big enough and keep repeating it, people will  
eventually come to believe it. The lie can be maintained only for such  
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Re: Headphone vs HDMI audio
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1. It's NOT a headphone plug because the output level is too low for
headphones. It's a "3.5 mm line output". You would need a headphone
amplifier.
2. The Pi has no audio chip (DAC). It uses a simple(*) filter circuit
controlled by PWM. Sort of a manual 1-bit digital to analogue conversion by
the CPU.
3. The analogue out sounds horrible. But, they improved the circuitry for
the Pi3 and greatly improved the driver at some point. With that, it sounds
pretty good. I don't know if the improved driver is now standard, I guess
it might by. To be sure, add "audio_pwm_mode=2" to /boot/config.txt
4. HDMI output is digital. Quality of the sound on that end depends on
where you plug it in.
5. You might (I do) still get some noise/hiss/beep even when using the
hdmi. Annoying when quiet, not noticeable by me even at low music level, so
I put up with it. Not sure of the source. Maybe the whole setup is not
grounded well, maybe the power adapter of the Pi sucks, maybe the lcd
display+control board I plugged on top adds noise.
6. I get perfect quality from a Pi Zero with IQaudIO DACzero board and a
good old cinch cable.

* Relatively simple. Discussion:
https://hackaday.com/2018/07/13/behind-the-pin-how-the-raspberry-pi-gets-its-audio/

Re: Headphone vs HDMI audio
On 23/08/2019 05:08, A. Dumas wrote:
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Almost delata modulation! :-)

Actually 1 bit DAC PWN can be amongst the lowest distortion and highest  
quality ... the errors are down to timing issues rather than voltage  
issues as it were.

But you should be clocking pretty fast. and that makes timing harder


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I used a HifiBerry DAC board. Its pretty good

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--  
You can get much farther with a kind word and a gun than you can with a  
kind word alone.

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Re: Headphone vs HDMI audio
On 22/08/2019 18:54, bob prohaska wrote:
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I havent tried but I can assure you that cheap amps to drive headphones  
will be of low quality. And the DACs in pis are cheap and nastry tech too.

The HDMI should be pure digital and of far higher quality

If you want quality *analogue* audio, get a decent DAC.


--  
?The ultimate result of shielding men from the effects of folly is to  
fill the world with fools.?

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Re: Headphone vs HDMI audio
On Fri, 23 Aug 2019 08:20:29 +0100

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    There are some surprisingly good (not great) op-amp based ones (Cmoy
derivatives) that aren't too expensive especially as kits.

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    That they are.

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    Depending on the DAC it meets.

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    Or start analogue and keep it that way which is *much* more
expensive and doesn't work when a computer is involved.

--  
Steve O'Hara-Smith                          |   Directable Mirror Arrays
C:\>WIN                                     | A better way to focus the sun
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Re: Headphone vs HDMI audio
Op 23-08-19 om 10:43 schreef Ahem A Rivet's Shot:
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It does not have an audio DAC chip, or any DAC or ADC chip. Audio  
circuit schematic for the Pi4 at the bottom centre here:  
https://www.raspberrypi.org/documentation/hardware/raspberrypi/schematics/rpi_SCH_4b_4p0_reduced.pdf
(audio is identical on the 3 en 4 but they cleaned up the drawing a bit  
in this version)

Re: Headphone vs HDMI audio
On 23/08/2019 11:26, A. Dumas wrote:
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It still has a DAC though

Even if its a couple of PWM outputs from te Pi main chip

Audio
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Where is the rest of the schematic? What drives PWM1_MOS1 and 2?

--  
"What do you think about Gay Marriage?"
"I don't."
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Re: Headphone vs HDMI audio
Op 23-08-19 om 12:59 schreef The Natural Philosopher:
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Mostly proprietary SoC, Broadcom ARM version with their VideoCore GPU. I  
have no idea what's in there, but the Pi doesn't have hardware PWM or  
analogue gpio pins.

https://en.wikipedia.org/wiki/Raspberry_Pi#Specifications

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