frame rate?

nilnil
edited April 2013 in General App Discussion

I looked at some recordings I did using audiobus and they all have a somewhat broad frequency peak between 40-something and below 60. Is this related to the frame rate on iOS (app trying to set it to 60 Hz?)? Do all sounds recorded on iOS have this because of the frame rate the apps are running at?

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Comments

  • Interesting. Youre the first person that i know to bring this up. are you using a frequency analyzer? same apps or diff ones all using audiobus?

  • Is this audio from the mic? I know that the built-in mic has noise on the low end of the frequency spectrum, and I could believe that it lands in that range. If I hook up an Apogee Jam and my guitar, I don't any noise (possibly some filtering happening in the Jam).

    With a synth, there should be no noise or frequency tweaking -- whatever they synth generates gets passed straight through.

  • I'm confused.. I don't see the connection between frequency and frame rate. I thought frame rate was the screens refresh rate, in which it would refresh X number of frames per second. I could see that a high cpu load would lower your frame rate.. But I can't see that the frame rate would interfere with recorded audio by trying to raise or lower the frequencies.. I didn't think the two were connected like that.. Are we talking a different kind of frame rate here? Sorry, I can't help. Just don't have a clue what we are talking about over here and i'd like to.. lol

  • The screen refreshes at about 60hz (the actual frame rate would be capped at that -- no point in pushing more frames). It seems plausible that this would create some electrical noise that would impact the microphone.

  • I understood what you said (sort of) @secretbasedesign but i wasn't sure if @nil was talking about noise.. He didn't say noise.. He said frequency.. And i got the impression it wasn't about the microphone.. the connection between frame rate and a broad frequency peak is where i get lost. I'm curious to why frequency analyses is needed... Is this a question of noise?

  • @ryan - sorry, I should correct myself. i meant spectral analyzer. Thats the only tool I could think of that would be accurate enough to give a gauge of a track's dominant frequencies.

  • There are spectrum analyzers (https://itunes.apple.com/us/app/spectrum-analyzer/id490078884?mt=8 is a good one), where the 60-ish Hz spike is easy to see (and the octave is there too). You can sort of see it on my spectrum analysis tool Spectral Eye (https://itunes.apple.com/us/app/spectral-eye/id546934084?mt=8), although this sort of stuff is not really what my app is designed for.

    If there's a spike showing up in the frequency spectrum, it's coming from somewhere. Could just be ambient sound (refrigerator, etc, something that vibrates at 60Hz to generate the noise coming in).

  • Just tried a Shure SM58 plugged in through the Apogee Jam -- with the gain cranked up, there's still something showing up at around 60Hz, but the level is much lower than the built-in mic. As much as 20 or 30 dBs. I think the reasonable conclusion is that you don't want to use the built-in mic (iPad3) if you have another option!

  • I t sounds to me ,that you are picking up the power net frequensie (50 hz in europe 60 hz in the us)
    Try keeping your Ipad mic and mic cable away from powerlines and power transformers.
    what was your exact setup?

  • edited April 2013

    Oh hahaha I see what's going on here! LOL Sorry man. I'm an idiot. I see why he thought the two were connected now.. I still don't think they are.. but he saw a frequency at 60Hz and the refresh rate is 60Hz so he thought the frame rate was adding the frequency because they are the same number. I'm pretty sure that Hz just refers to how many times something repeats per amount of time, i'm not 100% on that though... so that's why I don't think they are connected in that way.. but hell, my logic fails me all the time.. lol I do understand noise from the microphone or through the guitar even.. but in regards to giving it a number... I get lost. Is 60hz low or high?

    @Frank Do power lines buzz at 60Hz? I mean the sound you hear? Or is it something else?

  • Electrical lines and the wiring in your house always hum at 50/60Hz. Since it is always present you subconciously ignore it.

  • It's now April 2nd. End of thread? ;)

  • edited April 2013

    Regardless of whether or not this thread was a wind up, a 60Hz sound wave is just a bit flat of B1 on a keyboard. Ryan is right. Hz does not have to be frequency of sound, other types of wavecycles exist and can be measured in Hz.

  • It was not meant as a joke, I am just wondering where this peak comes from, electrical noise (50, 60Hz is a sharp peak that easily can be eliminated), but this one is about 10 Hz wide and coincidentally, the frame rate probably varies around some value in this range, so it was just something that came to mind. It does not create a problem, just curious what it is, artifact or not.

  • edited April 2013

    Could be an artifact of the input stage of the iDevice, few circuits have a flat response curve. May even be a deliberate bass boost to compensate for the built in mic.

  • edited April 2013

    @secretbasedesign - thanks, just downloaded ur spectral analyzer.

    this is probably the most technical thread ive ever seen on here (with exception of app developer code stuff) so I'm gonna throw this question out here for smarter ppl to elaborate on. what effect does audiocopy/paste/audiobus have on audio? and can it be app specific? so for example, if im using liveguitar and record it thru audiobus into say multitrack, and then copy and paste that track into say bm2, will there be a huge loss in fidelity? is it possible that apps can add or subtract certain frequencies?

    thnx in advance

  • @gjcyrus -- should be no meaningful loss in quality. The audio signal that gets sent out is essentially a series of sample values at 44.1k samples per second. Some apps do their math internally in 32-bit floating point (mine do), some use 16 bit integers. Converting from float to integer can lose some information -- but it's something that you can't hear (and you'd need very precise equipment to detect). I use floats for convenience, not because they give better quality.

    When the audio goes through the bus, or with C+P, it's in a raw, uncompressed, unmodified form. What goes in should be identical to what comes out. Conversion to MP3 does change things a bit -- but even that is usually pretty good.

    You can add/subtract/boost/damp frequencies (the various filter effects apps do that), but that's an intentional modification, not something that would happen unexpectedly.

  • The joy of digital sound is that there should be little or no degradation in sound quality no matter how many times it gets copied. Unlike analogue signals!

  • @secretbasedesign - thank you for the explanation! You should start a blog or something.

    @philw - agreed although i will say that bass and kick drum sounds good when recorded to 1/2 inch tape compared to digital and you can push the levels with tape unlike digital.

  • I did my first recordings with two cassette tape decks and a home-made mixer that allowed me to add an extra track with each bounce. It didn't take long before things got really muddy! Of course, that was back in the Stone Age...

  • @philw same for me. I learned to start bright. Best part was that one of my crappy decks ran a little fast so I'd I've have to retune on every pass!

    Then I got a Yamaha QX-1 and I've been a shitty keyboard player ever since. :)

  • edited March 2014

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  • Simon wrote: "1/4" reel-to-reel..."

    I did all my first recordings using a parakeet.

  • edited March 2014

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  • I had the tascam portastudios as well. But when you hear stuff on thicker stock tape like 1/2 inch or more, it's a diff sound.

    But yeah, I hear ya. the multiple times I bounced tracks, tape hiss would build and make it sound crap.

  • edited April 2013

    @Simon... I think if you play into a bottle and the put the cap on fast after you can send to a friend who can listen.. but it only works once! haha! :-) I don't know what the first recording device was... I thought the first recording device was the phonograph? I think THomas Edison was resposible for that... not sure though.

    EDIT: Googled it.. The phonograph wasn't the first recording device.. just the first one that had playback too.

  • edited March 2014

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  • edited April 2013

    @Simon http://en.wikipedia.org/wiki/Wire_recording

    Phonographs do predate them by about 20 years though. Neat.

  • edited March 2014

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  • Makes you appreciate what we've got now!

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