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<!-- #thumb --> <p>Sometimes my mouth runs faster than my common sense and caution, research and fact checking are sacrificed for the heat of the moment. *Such was my proclamation that there is no such thing as a stepped staircase waveform at the output of a DAC. *Instead, said I, there are a series of pulses that look more like lollipops and I presented a picture to prove my point. *While the pulses comment is indeed true, I left out “the rest of the story”. *Sorry.</p>
<p>John Atkinson, editor of <a href="http://www.stereophile.com" target="_blank">Stereophile Magazine</a>, was kind enough to send me a note reminding me that most multi-bit DACS also have a sample and hold circuit built into their outputs that actually makes the stair steps happen. *You’ll recall that in my post <a title="Hold that thought!" href="http://www.pstracks.com/pauls-posts/hold-thought/11550/" target="_blank">Hold that thought</a>*I explained the function of a sample and hold circuit on the input of the A/D converter. *That same type of circuit also exists at the output of many DACS so when the “lollipop” pulse happens, the level of that pulse is maintained by such a circuit and the result of that action is ….. wait for it ……. a stair step. *Take a look at this picture of the raw output of a DAC, from a <a href="http://www.stereophile.com/content/audio-note-cd-41x-cd-player-measurements" target="_blank">Stereophile article</a> of the Audio Note CD player:</p>
<p><a href="http://www.stereophile.com/content/audio-note-cd-41x-cd-player-measurements" target="_blank"><img class="alignleft size-full wp-image-11599" alt="Stepped waveform Running at the mouth" src="http://www.pstracks.com/wp-content/uploads/2013/09/Stepped-waveform.jpg" width="600" height="406" title="Running at the mouth" /></a></p>
<p>Note the steps? *So this happens because there is a pulse that goes to a specific height and once established a sample and hold circuit keeps that level constant until the next pulse.</p>
<p>Once you have this stepped waveform, it’s a pretty simple matter to remove all the jaggie steps with a simple filter and the result is a perfect sine wave.</p>
<p>And one last thought as long as we’re continuing to poke the proverbial box.</p>
<p>I have said before that if you have a vinyl disc and make a 44.1kHz/16 bit copy of that analog vinyl disc, the sound will be indistinguishable from the original. *This is because with vinyl or a tape recorder, you have a limited scope recording (vinyl and tape has limited everything relative to a CD) and capturing that limited recording on a CD is easy. *The opposite isn’t true.</p>
<p>A live event, recorded on a high resolution system, cannot be accurately copied on a lower resolution system such as a tape recorder or vinyl record.</p>
<p>And on that one, I have thought it through for quite some time.</p>
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[Source: http://www.pstracks.com/pauls-posts/running-mouth/11598/]
<p>John Atkinson, editor of <a href="http://www.stereophile.com" target="_blank">Stereophile Magazine</a>, was kind enough to send me a note reminding me that most multi-bit DACS also have a sample and hold circuit built into their outputs that actually makes the stair steps happen. *You’ll recall that in my post <a title="Hold that thought!" href="http://www.pstracks.com/pauls-posts/hold-thought/11550/" target="_blank">Hold that thought</a>*I explained the function of a sample and hold circuit on the input of the A/D converter. *That same type of circuit also exists at the output of many DACS so when the “lollipop” pulse happens, the level of that pulse is maintained by such a circuit and the result of that action is ….. wait for it ……. a stair step. *Take a look at this picture of the raw output of a DAC, from a <a href="http://www.stereophile.com/content/audio-note-cd-41x-cd-player-measurements" target="_blank">Stereophile article</a> of the Audio Note CD player:</p>
<p><a href="http://www.stereophile.com/content/audio-note-cd-41x-cd-player-measurements" target="_blank"><img class="alignleft size-full wp-image-11599" alt="Stepped waveform Running at the mouth" src="http://www.pstracks.com/wp-content/uploads/2013/09/Stepped-waveform.jpg" width="600" height="406" title="Running at the mouth" /></a></p>
<p>Note the steps? *So this happens because there is a pulse that goes to a specific height and once established a sample and hold circuit keeps that level constant until the next pulse.</p>
<p>Once you have this stepped waveform, it’s a pretty simple matter to remove all the jaggie steps with a simple filter and the result is a perfect sine wave.</p>
<p>And one last thought as long as we’re continuing to poke the proverbial box.</p>
<p>I have said before that if you have a vinyl disc and make a 44.1kHz/16 bit copy of that analog vinyl disc, the sound will be indistinguishable from the original. *This is because with vinyl or a tape recorder, you have a limited scope recording (vinyl and tape has limited everything relative to a CD) and capturing that limited recording on a CD is easy. *The opposite isn’t true.</p>
<p>A live event, recorded on a high resolution system, cannot be accurately copied on a lower resolution system such as a tape recorder or vinyl record.</p>
<p>And on that one, I have thought it through for quite some time.</p>
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[Source: http://www.pstracks.com/pauls-posts/running-mouth/11598/]