the one you link to has a 48 kHz samplerate,so while the 25 kHz is below the nyquist rate it would still suffer from phasing problems. for mathematical reasons, you want something only as high as the samplerate / 4. so in the case of 96 kHz you want a 24 kHz sine (or square wave). i'm going to refer to it as a 24 kHz wave from now on. i'm not sure why we were ever calling it a 25 kHz wave.
i'm actually a little confused by your drawing so i'm just going to explain with english, for a single turntable:
1 the input and output (post crossfader) of the mixer are split. the input is probably coming from SL, and the output is probably going to the PA. 2 the input split has a 24 kHz signal injected ("mixed") via the split. the signal has a low volume so it does not distort the audio going to the PA 3 the output split (or "tap") is going back to something that can analyze the amplitude of the 25kHz signal. this could be: a. a computer that is doing analysis in software b. an fpga that is doing analysis in hardware c. an analog circuit that is amplifying then bandpassing the signal at 24 kHz (or just high passing at 20kHz) and an arduino that is reading that value
for two turntables instead of one, it would make sense to simply inject the left channel on channel 1, and the right channel on channel 2, then tap both the left and right outputs separately.
> I think it'd be slick to put a phono + line audio inside of this box so you > plug USB to this box USB to Serato / Traktor box and you're good to go.
> the one you link to has a 48 kHz samplerate,so while the 25 kHz is > below the nyquist rate it would still suffer from phasing problems. > for mathematical reasons, you want something only as high as the > samplerate / 4. so in the case of 96 kHz you want a 24 kHz sine (or > square wave). i'm going to refer to it as a 24 kHz wave from now on. > i'm not sure why we were ever calling it a 25 kHz wave.
> i'm actually a little confused by your drawing so i'm just going to > explain with english, for a single turntable:
> 1 the input and output (post crossfader) of the mixer are split. the > input is probably coming from SL, and the output is probably going to > the PA. > 2 the input split has a 24 kHz signal injected ("mixed") via the > split. the signal has a low volume so it does not distort the audio > going to the PA > 3 the output split (or "tap") is going back to something that can > analyze the amplitude of the 25kHz signal. this could be: > a. a computer that is doing analysis in software > b. an fpga that is doing analysis in hardware > c. an analog circuit that is amplifying then bandpassing the signal > at 24 kHz (or just high passing at 20kHz) and an arduino that is > reading that value
> for two turntables instead of one, it would make sense to simply > inject the left channel on channel 1, and the right channel on channel > 2, then tap both the left and right outputs separately.
> On Sat, Feb 11, 2012 at 1:20 AM, Michael Auger <mich...@lm4k.com> wrote: > > Kyle,
> > If i understand the idea to track the fader using 25khz this box should > do > > the trick.... I think.
> > I think it'd be slick to put a phono + line audio inside of this box so > you > > plug USB to this box USB to Serato / Traktor box and you're good to go.
yeah that's much more understandable. the only clarifications would be:
- i don't think of the SL output as going "through" the injector, there's just a T junction there. but it works either way. - the output from SL and output from the mixer are stereo, and it's important that only one channel is tapped. this is what allows to distinguish from left volume from right volume. if the fader was linear we would only need one, but since the fader is not linear we need both.
On Wed, Feb 15, 2012 at 5:05 AM, Michael Auger <mich...@lm4k.com> wrote: > I got 25kHz from knowing there was some tone that I couldn't remember and > just throwing 25kHz on it to show something was added.
> Here is an updated version of the picture, this time with more color. ... > and straighter lines.
> In addition to what you have said, this is splitting the phono output from > the turntable and sending that to the computer to track the vinyl position.
> On Wed, Feb 15, 2012 at 3:29 AM, Kyle McDonald <k...@kylemcdonald.net> > wrote:
>> the one you link to has a 48 kHz samplerate,so while the 25 kHz is >> below the nyquist rate it would still suffer from phasing problems. >> for mathematical reasons, you want something only as high as the >> samplerate / 4. so in the case of 96 kHz you want a 24 kHz sine (or >> square wave). i'm going to refer to it as a 24 kHz wave from now on. >> i'm not sure why we were ever calling it a 25 kHz wave.
>> i'm actually a little confused by your drawing so i'm just going to >> explain with english, for a single turntable:
>> 1 the input and output (post crossfader) of the mixer are split. the >> input is probably coming from SL, and the output is probably going to >> the PA. >> 2 the input split has a 24 kHz signal injected ("mixed") via the >> split. the signal has a low volume so it does not distort the audio >> going to the PA >> 3 the output split (or "tap") is going back to something that can >> analyze the amplitude of the 25kHz signal. this could be: >> a. a computer that is doing analysis in software >> b. an fpga that is doing analysis in hardware >> c. an analog circuit that is amplifying then bandpassing the signal >> at 24 kHz (or just high passing at 20kHz) and an arduino that is >> reading that value
>> for two turntables instead of one, it would make sense to simply >> inject the left channel on channel 1, and the right channel on channel >> 2, then tap both the left and right outputs separately.
>> On Sat, Feb 11, 2012 at 1:20 AM, Michael Auger <mich...@lm4k.com> wrote: >> > Kyle,
>> > If i understand the idea to track the fader using 25khz this box should >> > do >> > the trick.... I think.
>> > I think it'd be slick to put a phono + line audio inside of this box so >> > you >> > plug USB to this box USB to Serato / Traktor box and you're good to go.
I have a fairly nice fpga if anyone wants to borrow it to try to do this. I hate writing VHDL (i.e. I'm terrible at it and forgot it after I learned it) It is currently in storage and I'll be bringing it to NYC with the rest of my gear in a couple weeks.
On Wed, Feb 15, 2012 at 12:57 PM, Dan Moore <d...@eachscape.com> wrote: > > b. an fpga that is doing analysis in hardware
> I have a fairly nice fpga if anyone wants to borrow it to try to do > this. I hate writing VHDL (i.e. I'm terrible at it and forgot it > after I learned it) It is currently in storage and I'll be bringing it > to NYC with the rest of my gear in a couple weeks.
On Wed, Feb 15, 2012 at 1:22 PM, quin kennedy <quinkenn...@gmail.com> wrote: > hmmm, I could try to remember some VHDL...
> On Wed, Feb 15, 2012 at 12:57 PM, Dan Moore <d...@eachscape.com> wrote:
>> > b. an fpga that is doing analysis in hardware
>> I have a fairly nice fpga if anyone wants to borrow it to try to do >> this. I hate writing VHDL (i.e. I'm terrible at it and forgot it >> after I learned it) It is currently in storage and I'll be bringing it >> to NYC with the rest of my gear in a couple weeks.
