H5 - Pure tones recording/playback and weird sound

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left13
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H5 - Pure tones recording/playback and weird sound

Post by left13 » Sun Sep 11, 2016 7:06 am

Hello,

When i record/playback pure tones ( sine waves ) there are several weird tones among with the current one.
This is happening close to -6 db and it's easier to hear on high frequencies.

It's also happening when i use it as an audio interface, by playing sine waves from Pc .
It starts at about 60% and up of pc volume.

Cannot notice it in anything else (like music,sounds) except when i record or play sine waves.

Is it normal ?

Thanks,
Lef
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Re: H5 - Pure tones recording/playback and weird sound

Post by Wulfraed » Sun Sep 11, 2016 8:44 am

Can't speak for the audio interface side, but if you are recording in MP3 format, it /might/ be an artifact of the MP3 compression.

Also, take into account sampling theory: You need to sample at twice your highest signal frequency to record that frequency -- but you won't be recording the wave shape at that limit; the best you record is a triangle wave (and you might not even get the full amplitude if your sample points aren't aligned with it).

At 44.1kHz sampling, even a sine wave at 11kHz will be something like an uneven square wave. And since square waves are made up of lots of harmonics...

Avenues for exploration would be to feed the input and output signals to an oscilloscope for comparison, and maybe running an FFT over them. A pure sine wave should have just one peak in the FFT.
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Re: H5 - Pure tones recording/playback and weird sound

Post by left13 » Sun Sep 11, 2016 11:46 am

Wulfraed wrote:Can't speak for the audio interface side, but if you are recording in MP3 format, it /might/ be an artifact of the MP3 compression.
It's wav format.

1)
I just tried as an audio interface - sampling 44.1kHz - full volume.
Each frequency sounds clear but weird distortion starts at 7463 Hz and goes really bad from there ( mixed tones and distorted like sound ).
I have to turn down the volume a bit to have clear sound for each 500/1000 Hz i go up.

For example:
20 - 7462 Hz - 100% volume (clear sound)
7463 - 8100 Hz - 92% volume (clear sound) (93%++ volume - distorted sound)
8100 - 8900 Hz - 85% volume (clear sound) (86%++ volume - distortion sound)
etc...

2)
In record mode i can see and hear clipping/distortion close to -6dB on the zoom meter only on loud high frequencies.
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Re: H5 - Pure tones recording/playback and weird sound

Post by greenA2 » Sun Sep 11, 2016 2:33 pm

Wulfraed wrote:Can't speak for the audio interface side, but if you are recording in MP3 format, it /might/ be an artifact of the MP3 compression.

Also, take into account sampling theory: You need to sample at twice your highest signal frequency to record that frequency -- but you won't be recording the wave shape at that limit; the best you record is a triangle wave (and you might not even get the full amplitude if your sample points aren't aligned with it).

At 44.1kHz sampling, even a sine wave at 11kHz will be something like an uneven square wave. And since square waves are made up of lots of harmonics...
I don't think this is how things work, there's probably a low pass filter at the output of the digital to analogue converter to cut anything above 20 kHz coming out. In the analogue part of the circuit the 11 kHz sine wave will be as close to a sinewave as it gets, and you shouldn't hear any harmonics. There might be a performance figure for total harmonic distortion somewhere.

Artifacts of mp3 are a different story, but even there I'd expect it to work well with sinewaves, and less well with square waves etc.
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Re: H5 - Pure tones recording/playback and weird sound

Post by left13 » Wed Sep 14, 2016 10:06 am

I contact zoom and it turned out to be a fault of the device.
I hope that they will fix it.

Thanks for the replies.
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Re: H5 - Pure tones recording/playback and weird sound

Post by simonkeys » Sun Mar 26, 2017 5:17 pm

I think I'm getting the same problem with my H5, at least for recording when using it as an audio interface. I haven't tested it carefully when recording in stand-alone mode yet.

Did you ever get anywhere with Zoom?
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Re: H5 - Pure tones recording/playback and weird sound

Post by left13 » Mon Mar 27, 2017 2:47 pm

simonkeys wrote:
Sun Mar 26, 2017 5:17 pm
I think I'm getting the same problem with my H5, at least for recording when using it as an audio interface. I haven't tested it carefully when recording in stand-alone mode yet.

Did you ever get anywhere with Zoom?
I sent it to the store that i bought it from, and they have checked it.
Their conclusion was that everything was normal and the issue was me trying to record at too loud volume, overdriving it at the input.
Still doesn't answer why do i see clipping leds below 0dbfs(close to -6) at monitor...
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Re: H5 - Pure tones recording/playback and weird sound

Post by Wulfraed » Tue Mar 28, 2017 10:11 am

left13 wrote:
Mon Mar 27, 2017 2:47 pm
Still doesn't answer why do i see clipping leds below 0dbfs(close to -6) at monitor...
Not sure just where you are looking... I have a few devices* where the warning indicator is designed to start flickering at -6dB, rather than only at 0dB. The manual for the H5 (pg 23) explicitly states that you should set the level so the majority of the signal is at -12dB or less; that gives a 12dB margin for impulses that exceed -12dB but are too short to really register on the display.




* just look at the list in my signature block :roll: Don't recall exactly which devices have it, but I do know at least one has the -6dB warning point.

The HD16 actually inflicts a two-step -- each input has a PEAK/Gain which is supposed to just flicker on the loudest parts, but all inputs feed through a single CLIP/RecLevel which is not supposed to flicker at all! BR-600/BR-800 is similar, using a common RecLevel, with the instruction to adjust for -12dB, since the BR actually display input level meters.
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Re: H5 - Pure tones recording/playback and weird sound

Post by left13 » Wed Mar 29, 2017 3:07 pm

Wulfraed wrote:
Tue Mar 28, 2017 10:11 am
left13 wrote:
Mon Mar 27, 2017 2:47 pm
Still doesn't answer why do i see clipping leds below 0dbfs(close to -6) at monitor...
Not sure just where you are looking... I have a few devices* where the warning indicator is designed to start flickering at -6dB, rather than only at 0dB. The manual for the H5 (pg 23) explicitly states that you should set the level so the majority of the signal is at -12dB or less; that gives a 12dB margin for impulses that exceed -12dB but are too short to really register on the display.




* just look at the list in my signature block :roll: Don't recall exactly which devices have it, but I do know at least one has the -6dB warning point.

The HD16 actually inflicts a two-step -- each input has a PEAK/Gain which is supposed to just flicker on the loudest parts, but all inputs feed through a single CLIP/RecLevel which is not supposed to flicker at all! BR-600/BR-800 is similar, using a common RecLevel, with the instruction to adjust for -12dB, since the BR actually display input level meters.
I am looking at device's meter-bars.
I can only see clipping leds below 0dbfs when i try high frequencies but lower freqs do clip exactly at 0dbfs.
Is this still possible and normal?(Maybe it's just its frequency response ? But isn't the meter supposed to be adaptive to different frequencies ?)
Thanks.
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Re: H5 - Pure tones recording/playback and weird sound

Post by Wulfraed » Thu Mar 30, 2017 9:37 am

The H5 does not have clip LEDs. It only has the LCD marker. LCDs are relatively slow devices to change (especially the reflective type that relies upon light passing through and getting polarized (blocked when dark, pass when background color). The level meter is based upon an average of input samples (there is no way the meter could respond to 44100 updates per second -- and is likely reporting the after A/D conversion values too). Clip indicator is likely handled by a hardware (analog) comparator on the input, before the A/D conversion, which latches a bit if the input voltage exceeds the "full" voltage of the A/D stage (OR, they could have just reserved the peak A/D output value to be used as clip indication).

In any case, the clip indication likely triggers on single samples, while the level meter is averages; a single clip level sample won't show in an average as anything more than a slightly higher peak.

As for frequency sensitivity -- higher frequencies do tend to carry more energy... And (hypothesis here) could fall into the sampling rate comparison easier. If more than one sample in sequence needs to be outside the A/D range before the clip indicator is set, a low frequency might need multiple samples from one sine cycle to exceed the threshold -- meaning the peak itself is noticeable above it; a higher frequency could possible be tested just at the peak of multiple sine cycles, meaning lower absolute peaks.
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Re: H5 - Pure tones recording/playback and weird sound

Post by left13 » Fri Mar 31, 2017 7:25 am

Wulfraed wrote:
Thu Mar 30, 2017 9:37 am
The H5 does not have clip LEDs. It only has the LCD marker. LCDs are relatively slow devices to change (especially the reflective type that relies upon light passing through and getting polarized (blocked when dark, pass when background color). The level meter is based upon an average of input samples (there is no way the meter could respond to 44100 updates per second -- and is likely reporting the after A/D conversion values too). Clip indicator is likely handled by a hardware (analog) comparator on the input, before the A/D conversion, which latches a bit if the input voltage exceeds the "full" voltage of the A/D stage (OR, they could have just reserved the peak A/D output value to be used as clip indication).

In any case, the clip indication likely triggers on single samples, while the level meter is averages; a single clip level sample won't show in an average as anything more than a slightly higher peak.

As for frequency sensitivity -- higher frequencies do tend to carry more energy... And (hypothesis here) could fall into the sampling rate comparison easier. If more than one sample in sequence needs to be outside the A/D range before the clip indicator is set, a low frequency might need multiple samples from one sine cycle to exceed the threshold -- meaning the peak itself is noticeable above it; a higher frequency could possible be tested just at the peak of multiple sine cycles, meaning lower absolute peaks.

Wow! Thanks alot for this valuable information. I'm starting to feel more proud of my device after all, it has already changed a faulty board so you know everything seems suspicious to me.
A professor of music tech also told me about the lcd not being able to show fast peaks, but wasn't sure. :)
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Re: H5 - Pure tones recording/playback and weird sound

Post by Wulfraed » Fri Mar 31, 2017 10:55 am

True LEDs with a proper driver algorithm would respond much faster (after all, they modulate them [or LASER diodes] to feed high speed communication over fiber optics).

LCD TVs/Flat Panel monitors tend to run on a 60Hz frame rate (I think some of the higher end models may handle 120Hz) {Don't get confused -- "LED flat panel" is still an LCD, but instead of using fluorescent tubes as the back light they use white light LEDs for the back light}.

44100 / 60 => 735 audio samples pass per display update.


Heh... And here I remember when Peak-reading LED meters appeared on stereo cassette decks... At that time, they used to recommend adjusting recording level for +3 to +6 dB! Two reasons: 1) Analog meters had response lag so a meter that was wiggling at 0dB was covering pulses up to +6dB; 2) magnetic tape has a smooth saturation effect rather than clipping -- sort of a built-in compressor. Now, with digital converters, all that has changed, and one needs to stay well down from 0dB -- my video cameras have distinct markers at -12dB.

One can post-process to normalize -- and if using a noise-gate filter, can block out anything below a certain level from even ending up in the final.
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Re: H5 - Pure tones recording/playback and weird sound

Post by simonkeys » Fri Mar 31, 2017 10:02 pm

left13 wrote:
Mon Mar 27, 2017 2:47 pm
I sent it to the store that i bought it from, and they have checked it.
Their conclusion was that everything was normal and the issue was me trying to record at too loud volume, overdriving it at the input.
Thanks for the update on your situation. I've been trying to investigate further, and now I think my problem is totally different from the one you had. I hear a sort of fluttering sound, like a random amplitude modulation, when using the H5 as an audio interface either for recording or playback, but not when using the H5 in stand-alone mode. I'll start another thread about it.
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Re: H5 - Pure tones recording/playback and weird sound

Post by left13 » Sat Apr 01, 2017 1:36 am

simonkeys wrote:
Fri Mar 31, 2017 10:02 pm
left13 wrote:
Mon Mar 27, 2017 2:47 pm
I sent it to the store that i bought it from, and they have checked it.
Their conclusion was that everything was normal and the issue was me trying to record at too loud volume, overdriving it at the input.
Thanks for the update on your situation. I've been trying to investigate further, and now I think my problem is totally different from the one you had. I hear a sort of fluttering sound, like a random amplitude modulation, when using the H5 as an audio interface either for recording or playback, but not when using the H5 in stand-alone mode. I'll start another thread about it.
I have those weird sounds like modulation too when i use it as an audio interface, but that happens after I turn up the volume after 80-90%(see my 2nd post) and only after I go above ~7500 Hz by testing pure tones.
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Re: H5 - Pure tones recording/playback and weird sound

Post by left13 » Sat Apr 01, 2017 1:38 am

Wulfraed wrote:
Fri Mar 31, 2017 10:55 am
True LEDs with a proper driver algorithm would respond much faster (after all, they modulate them [or LASER diodes] to feed high speed communication over fiber optics).

LCD TVs/Flat Panel monitors tend to run on a 60Hz frame rate (I think some of the higher end models may handle 120Hz) {Don't get confused -- "LED flat panel" is still an LCD, but instead of using fluorescent tubes as the back light they use white light LEDs for the back light}.

44100 / 60 => 735 audio samples pass per display update.


Heh... And here I remember when Peak-reading LED meters appeared on stereo cassette decks... At that time, they used to recommend adjusting recording level for +3 to +6 dB! Two reasons: 1) Analog meters had response lag so a meter that was wiggling at 0dB was covering pulses up to +6dB; 2) magnetic tape has a smooth saturation effect rather than clipping -- sort of a built-in compressor. Now, with digital converters, all that has changed, and one needs to stay well down from 0dB -- my video cameras have distinct markers at -12dB.

One can post-process to normalize -- and if using a noise-gate filter, can block out anything below a certain level from even ending up in the final.
So as long as I stay at -6dB / -12dB and eveything sounds crystal clear, i souldn't bother about distortion or such things on higher dBs ?
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Re: H5 - Pure tones recording/playback and weird sound

Post by Wulfraed » Sat Apr 01, 2017 10:15 am

Not quite: You may still need to experiment with your typical sources; but by trying to set the visual (meter) levels around -12dB with some pulses up to -6dB you should have a sufficient margin to handle most of the short sounds that might cause clipping.

Unfortunately, Zoom seldom publishes a frequency response chart for their products. Many microphones do tend to be more sensitive at the higher frequencies. cf: http://blog.shure.com/how-to-read-a-mic ... nse-chart/
http://www.kenrockwell.com/audio/zoom/h4n.htm shows a chart for the H4n -- which is practically flat from 100Hz to 1kHz, and has +6dB spikes at 5kHz and 6.5kHz, and is about +4/+5dB from 3kHz to 18kHz. Haven't found charts for the others.


Note: pure sine waves may also be triggering a resonance point with some components -- think swing set; if timed right, even small pushes will build to where the swing is covering nearly 90 deg arc... but if mistimed (different frequency) it just wobbles around erratically. The first link above mentions the use of pink noise (equal energy at all frequencies -- white noise is equal perceived volume at all frequencies as I recall) and then use a spectrum analyzer to develop the curve; they don't sweep pure tones across the spectrum.
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