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 Post subject: sample rate math problem
PostPosted: Fri Aug 19, 2011 12:57 am 
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say one wanted to emulate the same frequency of a sp 1200 while sampling in 45 rpm and then pitching down to save sample time, I know it would probably be impossible to completly emulate the sound because i dont know anything about 12 bit audio, i think only video cameras can create 12 bit audio files these day.

so the math problem

sp 1200 sample rate is 26.04 kHz

we need to know the sample rate if the record was playing at 45 rpm and then pitched down, i am assuming the khz will be lowered, but by how much is up to you math geniuses to help me with. please

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 Post subject: Re: sample rate math problem
PostPosted: Fri Aug 19, 2011 2:55 am 
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u can get conversion apps that will convert to any bitrate/sample rate..

As for the sample rate I'm not sure what you mean.. can u try n be a bit more clear about what is being recorded to where, which machine is pitching it down, etc?

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 Post subject: Re: sample rate math problem
PostPosted: Fri Aug 19, 2011 3:27 am 
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the record player plays at 45 sampled into the sp 1200.

inside the sp 1200 the sample is pitched back to 33 rpm,

the sample rate of the speeded up sample recorded into the sp 1200 will have a sample rate of 26.04 khz . when u slow the sample down the sample rate will still be at 26.04 but it will create an artificial alias with artifact noise. to compensate for it scientifically it needs to fit into the spectrum and it makes sense because when you shift sample rates it just affects the playback speed. infact sample rate just means playback speed. sorry for repeating myself, and not being clear the first time

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 Post subject: Re: sample rate math problem
PostPosted: Fri Aug 19, 2011 10:20 am 
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I think you have a wrong idea what sample rate means... sample rate definitively is NOT playback speed, if you sample a song using 16 bit 44.1kHz at certain speed and then you lower down or speed it up and sample again with the same bit/kHz rate you still having both different samples at different speeds but same sample rate... sample rate means the number of samples per unit of time and it only compromise audio fidelity... let's say if you have higher sample rate then you sound has more fidelity which it means that your sample sound sounds more similar to the original sampled sound... then if you sample at lower sample rate your sound it is not that similar reason why samplers at 12 bit or less sounds crispier... speed have nothing to do with sample rate.

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 Post subject: Re: sample rate math problem
PostPosted: Fri Aug 19, 2011 11:11 am 
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I still don't really understand what your end goal is

If you want samples to play at 26.04khz after they're pitched down from 45 to 33 you will need to originally sample them at 26.04x(45/33.33) khz..

if you pitch something down on an oldfashioned device there is no complicated algorithm necessary, it simply plays as though the sample rate is slower, 'holding' the current sample value until a point in time when the next sample begins..

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 Post subject: Re: sample rate math problem
PostPosted: Fri Aug 19, 2011 2:04 pm 
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thanks cartesia,

and yea locotesmjr, sample rate is playback speed and the capture rate of frames, you have to play them back at the same speed as you recorded them, if you slow the sample down the sample rate doesnt change, but is equivilent to changing the sample rate. try this, make a bunch of waves at different sample rates in 16 bit, load them into your sp and they will all play at different speeds, samples do not have to be 44100 to play in the sp, they just need to be 16 bit,

i dont know what my goal is anymore :shock:

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 Post subject: Re: sample rate math problem
PostPosted: Fri Aug 19, 2011 3:09 pm 
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If you sample a sound at 16 bit in different kHz and then you play them back all that you are going to get it is the same sound at different quality... but NOT at different speeds :wink:

Sample rate it is directly related to audio quality/fidelity not to speed...
higher sample rate = better sound quality/fidelity
lower sample rate = lo-fi

If you ever go to an studio they use 24bit 96kHz in studio sessions, that's because they want to achieve the best audio quality possible... if sample rate would be related to speed then using that high sample rate your voice would sound like quasimoto lol...

If you sample a record using a 12bit sampler 22kHz you get that crispy sound just because the audio it is sampled a lower resolution which means you get less sample per second which translate in a crispier sound because the A/D conversion... that's it, nothing to do with speed.

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 Post subject: Re: sample rate math problem
PostPosted: Fri Aug 19, 2011 3:16 pm 
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I already know that but I researched online to give you some more info, check this:

Both sample rate and sample format have an impact on potential sound quality. The capabilities of your audio equipment, and your intended use of the audio signal will determine the settings you should use.
Sample rate and sample format are only part of what determines overall sound quality. Sound quality is subjective, so you must experiment to find the audio interface and settings that work best for what you do


as you can see, sample rate and bit rate it is only related to audio quality...

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 Post subject: Re: sample rate math problem
PostPosted: Fri Aug 19, 2011 3:20 pm 
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In another note I thought your main goal it is to emulate the SP1200 12 bit sound...
well all that you need to do is play with your knobs and the lo-fi effect, see pic below (I found this pic here in the forum)

Image

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 Post subject: Re: sample rate math problem
PostPosted: Fri Aug 19, 2011 3:41 pm 
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thanks man, that will help me emulate the sound, but still you must understand that using different sample rates is the same as how regular tapes play really fast in a 4 track and the 4 track tapes play really slow on regular cassete players. when people in a studio record at 24 bit 96 khz they have to play the recorded session back in the 24 bit audio format at 96 khz. if you tryed to play this at 44100 khz 16 bit it would sound like loud white noise, this is because the session encoding is playing back the 24 bit 96 khz audio at the same sample rate as it was recorded at.

there is 3 main elements of the audio wave data that I know about. r.

the bit rate, the bit depth and the sample rate. all effect the quality of the audio in different ways and there is unlimited combinations of how to use them togethe

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 Post subject: Re: sample rate math problem
PostPosted: Fri Aug 19, 2011 4:24 pm 
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locotes,

if a machine plays samples at 44khz and you load a 22khz sample, it will play back 1 octave higher..

this is because the sampler doesnt say 'this is 22khz'

it just says:

read 44000 samples/frames per second.

if you read 44000 samples per second, then 2 seconds of 22khz audio will play back in 1 second (twice as fast, therefore frequencies doubled = +1 octave)

There is a tag stored in wav files that specifies the sample rate I believe (because thats the only way to tell what speed it's meant to be played back at), but old samplers that only support 1 playback samplerate dont bother reading it at all.. they just say 'get next sample/frame, get next sample/frame' according to their internal clock

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 Post subject: Re: sample rate math problem
PostPosted: Fri Aug 19, 2011 4:28 pm 
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this should help validate my claim

http://unsatisfiedpoets.org/sp/samplerate

i encourage you to inspect the files to show that sample rate genuinely Does directly effect playback speed,

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 Post subject: Re: sample rate math problem
PostPosted: Fri Aug 19, 2011 4:49 pm 
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this is epic!

http://www.youtube.com/watch?v=AIUoLXZ_w8c

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 Post subject: Re: sample rate math problem
PostPosted: Fri Aug 19, 2011 4:58 pm 
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Ok, now I understand what both you and cartesia are saying but I never thought that way because I assume that if you are sampling at lo-fi sampler then you are going to play those samples in the same sampler, I always sample in lo-fi using my 505 and sequence also there, then bounce my track to Pro-tools in 24bit-96kHz and the sample speed never change... I never tried to sample in 22Khz and playing those in 44kHz doesn't make sense to me... why I should do that?

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 Post subject: Re: sample rate math problem
PostPosted: Fri Aug 19, 2011 5:18 pm 
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when you record your lofi into pro tools all it does is capture the lofi essence, this is a form of upsampling, typicly the higher sample rate you record at will give you a better sound because it is capturing more frames per milisecond. for example say you have a 8 bit sample, and you record it into your sp, the sample is no longer 8 bit, it is now 16 bit 44100, but the lofi essence has been captured at 44100, i dont know why I am saying essence, haha. anyway, now the sample is at 16 bit 44100, upsampled and bit shifted from 8 bit whatever hz. as there is different combinations of these audio elements, the possible ways of converting formats and shifting bits and frequencies is mind numbing. so back on track, I will estimate the sample rate I am looking to achieve is somewhere around 11000 and 16000 khz but I have no way of generating true 12 bit audio so my is experiment is already flawed.

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