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Can a daw be bit-perfect multitrack?
Old 3 weeks ago
  #1
Gear Head
 

Can a daw be bit-perfect multitrack?

Is it possible to multitrack on the computer but avoid any dsp calculations to the recorded audio in playback?

If I set my daw's (logic) sample rate and bit depth to match my AD and DA and send each track to a dedicated output for external summing, have no bussing, faders at zero, no panning and no edits will the numbers going out to the DA on each track be exactly the same as the numbers recorded?

Is Dither or any other hidden maths applied?

I have looked but can't find the answer.
Old 3 weeks ago
  #2
Quote:
Originally Posted by pianoscope View Post
Is it possible to multitrack on the computer but avoid any dsp calculations to the recorded audio in playback?

If I set my daw's (logic) sample rate and bit depth to match my AD and DA and send each track to a dedicated output for external summing, have no bussing, faders at zero, no panning and no edits will the numbers going out to the DA on each track be exactly the same as the numbers recorded?

Is Dither or any other hidden maths applied?

I have looked but can't find the answer.
The only one that can really answer is the developer. My guess is that it’s possible.

But some parts of the process should be easy to test. Record a piece of music. Export it, import it, flip phase. Should null if you align it right.

What’s the reason for asking? (It might be easier to get answers if people know what you want to achieve.)
Old 3 weeks ago
  #3
Lives for gear
 

FYI, with Core Audio, it isn't the DAW's job to convert the audio from 32-bit floating point to 24-bit integer for your audio interface. That's the audio driver's job.

Also, the audio HAL's internal format is 32-bit floating point, so Logic can just feed 32-bit floating point buffers to the HAL without any format conversion. The HAL can then just pass these 32-bit floating point buffers to the audio driver without any conversion to 24-bit integer.

Core Audio output drivers then do the conversion (and clipping) to 24-bit integer.


As to whether Logic *pre-dithers* the 32-bit output audio stream? I've seen conflicting information, although the last thread I read on this over at Logic Pro Help (by user Lagerfeldt), IIRC, finally came to the conclusion that Logic wasn't doing any dithering (although he initially thought it was doing some dithering).

Last edited by DanRand; 3 weeks ago at 12:52 AM..
Old 3 weeks ago
  #4
Lives for gear
Should not be that hard to verify. Record a known source through a digital input. CD with spdif. Rip the CD and do binary compare.
Send your digital out back through spdif and compare again.
I dont think it's a problem with floating point, it should cover your digital input without loss.
But you will get DSP in your ADDA.
Old 3 weeks ago
  #5
Gear Head
 

Cheers for responding to these very basic questions.

I’m trying to learn a bit more about how digital audio works

Digital mixing/recording seems to follow the same law as analog, the less processing done in the signal path the better. The sonic degradation caused by dsp processing seems to be different to analog.
I'm reasonably happy with the sound from the daw when I don’t use any plugins, just internally debating whether to explore converters a bit more.

I did think of spdif or capturing the adat stream, but currently don’t have the right gear, but thanks for the tip.

So if logic (I also have PT) puts out 32bit float that gets converted to 24 bit fixed, is it useful to add dither to the multiple outputs?
Old 3 weeks ago
  #6
Lives for gear
 
JulenJVM's Avatar
Quote:
Originally Posted by pianoscope View Post
Is it possible to multitrack on the computer but avoid any dsp calculations to the recorded audio in playback?

If I set my daw's (logic) sample rate and bit depth to match my AD and DA and send each track to a dedicated output for external summing, have no bussing, faders at zero, no panning and no edits will the numbers going out to the DA on each track be exactly the same as the numbers recorded?

Is Dither or any other hidden maths applied?

I have looked but can't find the answer.
You can use a plugin like the free Bitter from Stilwell audio to check the bit depth of each audio stream. I've done some checks myself in Cubase, as long as there is no processing on the channel (pan, gain, buss summing, etc...), the data stream on each track remains at 24 bit (my bit depth of choice for mixing). I assume other DAWs do the same, it's worth checking by yourself.

As soon as there is some DSP involved, the audio is processed at FP (32 or 64 bit). In this case, it is advisable to add 24 bit dither just before the hardware insert, as the signal will be truncated from FP to 24 bit. The theory says to always dither when reducing bit depth, although some say they can't hear a difference...
Old 3 weeks ago
  #7
Lives for gear
Quote:
Originally Posted by pianoscope View Post
Digital mixing/recording seems to follow the same law as analog, the less processing done in the signal path the better.
For purist, yes.
Otherwise processing could be a goal.
Old 3 weeks ago
  #8
Gear Guru
 

Quote:
Originally Posted by pianoscope View Post
I’m trying to learn a bit more about how digital audio works

Digital mixing/recording seems to follow the same law as analog, the less processing done in the signal path the better. The sonic degradation caused by dsp processing seems to be different to analog.
I'm reasonably happy with the sound from the daw when I don’t use any plugins, just internally debating whether to explore converters a bit more.
You'd have to weigh more conversion stages against processing digitally then. I think the jury is likely out on which is better or worse. Dither for example is just noise. Noise is part of what you get when you convert + more noise through the analog processing you'd do... so...

Quote:
Originally Posted by pianoscope View Post
So if logic (I also have PT) puts out 32bit float that gets converted to 24 bit fixed, is it useful to add dither to the multiple outputs?
I believe most will recommend dithering as the last step in production, not continuously throughout.
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