Audio mismatch issues


#1

I’m having trouble with the audio skipping on my facebook stream. I always have this message on my epiphan screen: “Actual audio sample rate 44713.20Hz mismatched with expected (44100Hz or 48000Hz). Check your HDMI IN audio settings” Where are these HDMI IN audio settings? Is this mismatch the reason I’m having a skip/stutter on my streams? Does the audio have to be EXACTLY 44100 or 48000Hz? I’m using an Ocean Matrix Video to HDMI Pro Mini Converter/Scaler OMX-CV-HDMI to combine video and audio to send via HDMI to the webcaster.


#2

This is just a warning message and can generally be ignored without any issue. This is simply reporting that the incoming audio sample rate differs from our expected rate. For example we would be expecting 44100 Hz but in this case are receiving 44713Hz.

Stutter in streams is more likely due to a bandwidth issue. I would recommend running a speedtest: google.com/search?q=speedtest and then making sure the bitrate setting on the Webcaster is no more than 50% to 70% of this available upload speed. For example for a 2048Kbps bitrate you would be advised to have at least a 3Mbps upload speed with 4Mbps or greater being ideal. Also worth noting is that other users could affect the available upload speed, it is best to limit other activities on your internet connection during a stream to avoid this.


#3

Thanks for the reply. That’s good to know. If it really isn’t a problem, I just wish it wouldn’t even tell me about the mismatch. We are using this in a church setting and having an error message pop up will just cause unnecessary concern on my team. Also, since the display on the X2 says “Invalid Samplerate,” it doesn’t show the stream time.
Not a big deal- I’ll just have to make sure everyone knows.

This Webcaster X2 really is a great device. Thanks to Epiphan for making such a great product!


#4

I agree, I will pass the feedback on! Let me know if anything else comes up that I might be able to assist with!


#5

We just connected a USB Audio feed from our Mackie ProFx16v2 sound board and we are getting a similar message “actual audio sample rate 43933.99 hz mismatched with expected 44100 hz or 48000 hz. Check your HDMI In audio settings” Looking at the specs that Mackie published regarding the USB I/O they read: A/D/A 16bit, 44.1 kHz / 48 kHz. 2 questions… Is the on screen message from the Webcaster X2 missing a “k” in the freq or is the webcaster really only receiving 43934 hertz? Secondly- if the Mackie board is truly sending 44.1 kHz/ 48 kHz what is happening to the freq between the boards output and the webcaster input? Thx


#6

Hello,

k just means kilo or a thousand here, so 44.1 kHz is the same as 44100 Hz. The difference here of what we are detecting is very slight, and this is just an error message. In almost all cases this can be ignored.


#7

@AdamFrame The notes in this thread indicate that the audio stream will still play even if the error message is presented. However I think there need to be clarification. As of yesterday this chat with your support was held:
Chat thread with Epiphan support.

We have an Epiphan Webcaster X2 and recently replaced an SDI to HDMI converter that feeds the webcaster. With the new converter, the webcaster show an error message that the audio sample rate 44906.3Hz mismatched the expected. I found another message in the forum that this is just a warning, but when we had the problem there was no audio, just random clicks every few seconds. Should the webcaster have worked with the mismatched sample rate?

the Webcaster X2 only supports audio over HDMI at 44.1 and 48 kHz, anything else will either come through as clicks, or no audio at all

Sent by: Bot12:50 PM

My guess is that the 44906.3 Hz, which is 44.9063 kHz isn’t quite close enough to 44.1
Sent by: Bot12:51 PM

The fact is that this error does, in fact, indicate that the audio will not pass if the error message is presented. There is an implication in the above message that there is some error tolerance but it is not total as stated earlier in this thread. Since digital is an exact science, how can a processor determine that it can accept a certain sample rate that is a little out of range and therefore ok to pass signal but if the sample rate is a little bit more out of range it can’t pass the signal. There has to be a hard tolerance number somewhere in the system. If that is the case that number should be published so that we in the field can address it scientifically rather than doing a guess by trial and error as to whether a device will work with your system or not? The earlier thread is wrong and that needs to be clarified.


#8

I apologize if my message over chat was misleading. I did not mean to imply that there was a specific error tolerance or hard number the Webcaster X2 would accept before throwing an error and resulting in poor audio quality. I believe the issue has more to do with how audio frequency sampling works, and how devices are built/programmed to interpret audio signals.

The Webcaster X2 user guide states the following in regard to distorted audio,

“At this time, Webcaster X2 only supports HDMI audio in at 44.1 kHz or 48 kHz. Using other audio frequencies such as 32 kHz results in audio distortions that appear as background noise, pitch shifting, or other undesirable audio behaviors. If you’re experiencing any of these problems, check your input source to ensure the correct audio frequency is set.”

Essentially, what this means is that if the audio signal doesn’t match those sample rates you’re going to have distorted audio in some fashion. The error message is letting you know that the sample rates are mismatched, and has nothing to do with whether or not the audio is distorted or not coming through at all. It is the audio sample rate that dictates that, if it is too far outside what the hardware/software can understand you begin to see distorted or broken audio. It’s not because a specific value is coded somewhere, it’s simply how audio sampling works. Unfortunately, I am also not an audio engineer, so I am not certain of the specifics behind how and why this happens.

Ultimately, you want to make sure that your audio is coming in as close as possible to those listed values. As Adam said earlier in this thread, in most cases the mismatch error can be ignored, however, the further your sample rate gets from the supported frequencies, the more likely that error is going to be important and indicative of an actual problem that is going to affect your audio and stream.

If you’re interested you can read more about audio sampling here, https://en.wikipedia.org/wiki/Sampling_(signal_processing). For now though, you can also send us a ticket at info@epiphan.com so we can try to determine what’s going on with your audio source and the Webcaster X2 and get it working for you.