Geoff > OK, I won't say you're wrong. But I do disagree. Lol ;-) Are you suggesting there is some kind of phase locked loop to synchronise the D/A converter on the data rate ? Well, you probably are right, I don't know, and by the way, American cell phones are not the same technology as european GSMs... but ok, let's assume both have such a system. A PLL device is not perfect : because of the filtering involved between the phase comparator and the voltage controled oscillator, it might have good precision on the long term, but being slightly frequency modulated is such a way that you don't hear it, but it makes it not accurate enough for tuning. On the point of the clicks (and not point and click*) you should hear, since I don't know the size of the buffer on a cell phone, nor the sampling rate, it's rather difficult to calculate, but don't forget that to hear a click, you need you signal to be interrupted in an audible way. if you remove (approximately) one or more entire period of a sine wave, you will just hear (nearly) nothing. Now, if your D/A converter is slightly too fast, you could have blanks inserted from time to time instead of clicks, but because of interpolations that might be involved in the process, this blank might also go unnoticed. don't forget that to make a one cent error would lead to only one packet added or dropped every 1730... this is not much.... will you hear it ? * : I'm not even sure my sentence was correct, so this playing on word might as well be completely rotten ;-) I don't know... you might as well be right, but those are the reasons why I just wouldn't be too confident in it... that's why I suggested someone to test it. Philippe ----- Original Message ----- From: "Geoff Sykes" <thetuner at ivories52.com> To: "'Pianotech List'" <pianotech at ptg.org> Sent: Saturday, May 27, 2006 4:28 AM Subject: RE: ETDs, PCs,PDAs & cellphones vs tuning fork : how accurate are they ? > Philippe -- > > OK, I won't say you're wrong. But I do disagree. > > When the 440Hz tone is recorded, the bits and the bytes are all packaged > together in words that are created at a sampling rate of, say, 44.1KHz. Each > word contains a lot of other information, the most important being clock > speed synchronization data and error checking checksums. The clock speed in > the playback device can deviate a little bit without too much concern > because part of the D/A decoding process involves synchronizing circuits > that attempt to keep the playback clock the same as the sampling rate on the > source when it was created. > > When the playback clock can't correctly sync with the source clock, or it > locks at, dare I use the term partial of the source clock, then you start to > hear artifacts like ticks. If these clock rates deviate too much then it > just won't play at all. However, when it comes to decoding the data, if > error checking is not able to automatically correct small playback > conversion errors, then you start to hear things like dropouts. But > regardless of playback decoding and synchronization errors, the one's and > zero's are still in the same sequence and I contend, therefore, that the > tone will still be 440. > > I spent many years as a sound engineer in the music industry. My last > corporate gig was as a Mastering Engineer at A&M Records, in Hollywood. I'm > no stranger to digital either. But I don't know it all, and I'm the first to > admit there's always more to learn and understand. Just like piano > technology. > > -- Geoff Sykes > -- Assoc. Los Angeles > > > > -----Original Message----- > From: pianotech-bounces at ptg.org [mailto:pianotech-bounces at ptg.org] On Behalf > Of Philippe Errembault > Sent: Friday, May 26, 2006 5:31 AM > To: Pianotech List > Subject: Re: ETDs, PCs,PDAs & cellphones vs tuning fork : how accurate are > they ? > > > Hi Geoff, > > The problem is not in trasmission. what you listen to are not bytes in a > buffer, but the need to be re converted to analog sound. The problem is in > the digital to analog conversion. Let's assume one use a sampling rate of 44 > 100 Hz, like on CDs. you can always calculate the samples instead of really > recording them, so let's assume the recording was perfect. So a one second > 440Hz tone, will contain 44100 samples which will contain 440 period of a > sine wave. > > Now, imagine you play this sample on a sound device whose quartz is 1% too > slow. the real play back will only play 44100-441 = 43659 samples during the > first second. and so you will only play 440 * 43659/44100 = 440*99% = 435.6 > periods of the sine wave during this second and so the frequency of your > tone will be slowed down to 435.6 Hz. > > Please think well about it before saying I'm wrong, because I may be a > newbee in tuning but I'm definitely _not_ a newbee in digital sound > processing. ;-) > > Philippe Errembault > > ----- Original Message ----- > From: "Geoff Sykes" <thetuner at ivories52.com> > To: "'Pianotech List'" <pianotech at ptg.org> > Sent: Friday, May 26, 2006 6:54 AM > Subject: RE: ETDs, PCs,PDAs & cellphones vs tuning fork : how accurate are > they ? > > > > If the transmitting or storage medium of your source was analog then > > clock speeds, transfer, repeater and amplifier delays, and any number > > of other mishaps could indeed alter the frequency. Think speeding up > > or slowing > down > > a record player. (You do remember records, don't you?) > > > > Digital, on the other hand, is simply a collection of one's and zero's > > in > a > > very specific order. Regardless of clock speed, storage, transmission, > noise > > or any number of inconsistencies in the signal path, even if you > > deliberately change the speed the transfer process or processor > > clocks, those one's and zero's will ALWAYS arrive in exactly the same > > sequence in which they were sent. When they don't, the result is noise > > and dropouts, > not > > speed or frequency shift. In other words, a calibrated 440Hz tone sent > over > > a digital signal path will still be 440Hz at the receiving end. > > Changing > the > > pitch of a digital signal is possible, but it involves some serious > > and deliberate number crunching. > > > > Broadcast tones, ala WWV, I would not trust as absolutely accurate. > > Tones over the phone, unless you are absolutely sure there is no > > analog stage in the chain, I would also hold suspect. Also, once a > > digital signal has been converted back to analog it passes through > > amplifiers and a speaker so we can hear it. Unless those components > > are extremely high quality the end result might not be exactly spot > > on. But unless you have a precision frequency counter or a calibrated > > spectrum analyzer handy you probably > would > > not be able to tell. Just how accurate do you want to be? We're > > talkin' pianos here, not rocket science. > > > > -- Geoff Sykes > > -- Assoc. Los Angeles > > > > > > > > > > > > > > > > -----Original Message----- > > From: pianotech-bounces at ptg.org [mailto:pianotech-bounces at ptg.org] On > Behalf > > Of Robert Scott > > Sent: Thursday, May 25, 2006 6:59 AM > > To: pianotech at ptg.org > > Subject: Re: ETDs, PCs,PDAs & cellphones vs tuning fork : how accurate > > are they ? > > > > > > Philippe Errembault writes: > > > > > Do you usually have an idea of the precision of the A440 reference > > >you use ? I mean... I didn't get any the precision information with > > >my tuning fork, I found it on the net. I wonder what are the > > >precisions of professional ETDs, and what precision we can expect > > >from a pocket PC, about which I wonder if it even can be as precise > > >as a normal PC... > > > > If you have back-issues of the PTG Journal you might want to take a > > look > at > > "Calibration of Pitch References" in the August 2001 issue. It shows > > that all major ETDs are calibrated to better than .01 cents. The > > article also discusses tuning forks, their temperature dependency and > > accuracy, and how to calibrate them. > > > > > > > ...it might be that PDAs only contain ONE reference clock, for time, > > > for CPU and for sound processing. > > > > I have found that not to be true. In fact, even on the Pocket PCs, > > they sometimes have separate audio sample rate oscillators for the > > listening > mode > > and the sound-generating mode (recording and playback). As for the > > CPU clock, that is definitely not tied to the audio clock because the > > Pocket > PCs > > take advantage of switching to slower CPU clock speeds during idle > > times > to > > save on power. You can't have your audio processing clock tied to > > such a variable clock source. > > > > It really does not matter that the audio sample rate is not precise, > > as > long > > as it is stable. Once you do a software calibration on your ETD, the > > results are the same as if the oscillator were perfect to begin with. > > > > > > > There was also someone who claimed that listening a tone reference > > > through a cellphone was as good as with a normal phone. I know the > > > buffering of cell phone is small, but this doesn't change the fact > > > that any shift in it's clock should be retrieved in the output!.. > > > > You can depend on the frequency of sounds being delivered accurately > > over the cell phone network. There is no pitch distortion. What is > > unclear is whether the same can be said for the Voice-over-Internet > > Protocol Internet services that deliver telephone service through your > > computer. This is potentially subject to indeterminate TCP/IP > > buffering and perhaps pitch distortion. > > > > Robert Scott > > Ypsilanti, Michigan > > > > > > > > > > > >
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