Bit perfect, what does that mean?

[idc]

I see 'bit perfect' cropping up more and more. It is used to describe the transmission of music files to DACs. But it appears that to do that you need the likes of Foobar and WASPI or AISOL (or whatever it is). Then I read of wanting to make various passes when ripping a CD to make sure it is bit perfect.

But surely when I play itunes on my Vaio laptop with W7 and my music is sent to my DAC, it is bit perfect. When I rip a CD using itunes with error correction on, it is bit perfect. Or is it? Then how does Spotify fit into this? Is it 'bit perfect'?

I feel like I am losing out here by apparently not having 'bit perfect'.

 

[Gerrardasnails]

idc:
I see 'bit perfect' cropping up more and more. It is used to describe the transmission of music files to DACs. But it appears that to do that you need the likes of Foobar and WASPI or AISOL (or whatever it is). Then I read of wanting to make various passes when ripping a CD to make sure it is bit perfect.

But surely when I play itunes on my Vaio laptop with W7 and my music is sent to my DAC, it is bit perfect. When I rip a CD using itunes with error correction on, it is bit perfect. Or is it? Then how does Spotify fit into this? Is it 'bit perfect'?

I feel like I am losing out here by apparently not having 'bit perfect'.

The process of moving the bit perfect music file from pc or other device to DAC or amp usually plays around with the bit perfectness! For instance, WMP will output everything at 16bit 48khz. So a perfectly ripped cd at 44.1 will be changed. WASAPI and ASIO basically shield the music file from any such processing. This is how I understand it. If I'm wrong, please don't shoot me people!!

 

[idc]

That makes sense. But does that mean having such processing will change a lossy or lossless files bit rate? Or are we talking about another type of bit? Is that a byte?

 

[hammill]

A byte is a number of bits, almost always 8 these days.

 

[idc]

Since CDs are 44.1khz, why dont computers have that as an option to output? In any case I dont see how that affects the bits in my music files. So I do get a bit perfect file going to my DAC.

 

[davydmx]

I think for most people, the whole point of using Media Monkey/Foobar/J.River Media Centre, etc, on a pc instead of iTunes, is that they accomodate ASIO/WASAPI/Kernel Streaming, all of which allow your music files to 'exit' the pc unaffected by any nasty resampling, etc.

Actually, the term 'bit perfect' seems to get applied to slightly different things, but i think it's mostly used to describe the process above!

I'm still convinced that Foobar, used 'piggyback' with Itunes(Foobar/WASAPI for quality playback, iTunes for organisation of library, album art, syncing iPod, etc) is the ultimate way to go on pc. And not nearly as fussy as it sounds, either!

 

[Gerrardasnails]

davydmx:
I think for most people, the whole point of using Media Monkey/Foobar/J.River Media Centre, etc, on a pc instead of iTunes, is that they accomodate ASIO/WASAPI/Kernel Streaming, all of which allow your music files to 'exit' the pc unaffected by any nasty resampling, etc.

Actually, the term 'bit perfect' seems to get applied to slightly different things, but i think it's mostly used to describe the process above!

I'm still convinced that Foobar, used 'piggyback' with Itunes(Foobar/WASAPI for quality playback, iTunes for organisation of library, album art, syncing iPod, etc) is the ultimate way to go on pc. And not nearly as fussy as it sounds, either!

I agree, I've been using J River Media Center and WASAPI is built in so you just need to tick whether you want to use it or not in the audio options - hardly rocket science! I've now ditched my idea of using a pc as source (I have been using a Windows Media Center extender) and opened my new toy last night - HDX BD1. I've not checked yet whether it does bit perfect but it's supposed to offer audio pass through and I'm told it basically sends the files to DAC untouched. So, I won't be using the J River much now apart from as a library to formulate all my music before it goes to my external drive. The album cover download on it though is fantastic and I would be happy to keep it just for that.

 

[Anonymous]

davydmx:
I think for most people, the whole point of using Media Monkey/Foobar/J.River Media Centre, etc, on a pc instead of iTunes, is that they accomodate ASIO/WASAPI/Kernel Streaming, all of which allow your music files to 'exit' the pc unaffected by any nasty resampling, etc.

Isn't this a Windows problem, rather than an iTunes problem?

When playing CDs through my Mac, it says '44.1kHz' on the DAC display...

 

[davydmx]

Fahnsen:davydmx:
I think for most people, the whole point of using Media Monkey/Foobar/J.River Media Centre, etc, on a pc instead of iTunes, is that they accomodate ASIO/WASAPI/Kernel Streaming, all of which allow your music files to 'exit' the pc unaffected by any nasty resampling, etc.

Isn't this a Windows problem, rather than an iTunes problem?

When playing CDs through my Mac, it says '44.1kHz' on the DAC display...

Yes, i believe this is a Windows problem. But iTunes could've been the ideal, all round media software on pc, IF it could utilize WASAPI or similar.

But rather than that, Apple would probably tell us to go and buy Macs instead!

 

[The_Lhc]

idc:Since CDs are 44.1khz, why dont computers have that as an option to output? In any case I dont see how that affects the bits in my music files. So I do get a bit perfect file going to my DAC.

Bitrate is a function of the bit width (possibly not the correct term but it escapes me at the moment) and sample rate, the bit width is obvious, ie 16-bit, 24-bit etc, you understand that, it's the resolution the original waveform is sampled at, the higher the resolution the closer to the original analogue waveform the result is.

The sample rate is how often a set of 16 bit samples is taken from the waveform, for 44.1kHz it's 44,100 times per second, giving 705.6kbits/second, multiplied by two (stereo of course), gives you your CD bitrate of 1411.2kbit/s.

However if the PC is upsampling to 48kHz then that's 1536kbit/s, so where do the extra bits come from? The PC puts them in and it's either (educated) guesswork or it's padding and you have to ask yourself whether you really want that in your output?

So unless you're using one of the previously mentioned methods to stop your PC upsampling then you're not getting a "bit perfect" representation being sent to the DAC.

The above might not be completely accurate but I think it's close enough to be understandable. Whether it makes any (noticable) difference is another matter entirely...

 

[Anonymous]

davydmx:iTunes could've been the ideal, all round media software on pc, IF it could utilize WASAPI or similar.
But rather than that, Apple would probably tell us to go and buy Macs instead!

Well, leaving basic tasks to the OS is the Mac approach. I think it would need a cultural revolution in Cupertino to make applications that take care of 'OS business'...

 

[Anonymous]

Although sample _rate_ conversion SRC should be avoided, it is not true that windows always does it. If the only source is 44.1kHz/16bits Windows' kmixer will NOT resample (unless it knows that the audio device does not support this format, which is unlikely).

Volume control (ie less than 100%) is not SRC, but lowers the values of the (16bits) samples. This reduces the dynamic range and should probably be avoided also.

In general, both SRC and Volume control (or levelling) can work without a major sound quality effect (unless SR is very low, or volume is very low and than pumped up again by the amp): algorithms have good interpolation techniques. But as said, avoiding it is better.

BTW Volume control is possible in WASAPI too, in which case it is not bitperfect.

 

[Anonymous]

idc:

When I rip a CD using itunes with error correction on, it is bit perfect. Or is it?

Never ripped a cd with itunes, but enabling your drive's error correction will most likely give non bit perfect results if a read error occurs (since the drive will have to make up the information that it missed).

This is a good place to start reading up on the subject of Windows KMixer and the solutions for the problems it causes:

http://en.wikipedia.org/wiki/Audio_Stream_Input/Output

 

[idc]

Thanks for all of the replies. I take it that when talking about bit perfect there are two acceptable useages. A 'bit perfect rip of a CD to PC' and transmission of a 'bit perfect', unmixed or tampered with signal from PC to DAC.

Sillyoldman, I too will try out Windows Audio Session for itunes

 

[The_Lhc]

idc:Thanks for all of the replies. I take it that when talking about bit perfect there are two acceptable useages. A 'bit perfect rip of a CD to PC' and transmission of a 'bit perfect', unmixed or tampered with signal from PC to DAC.

Yup that's pretty much it.

 

[idc]

the_lhc:

idc:Thanks for all of the replies. I take it that when talking about bit perfect there are two acceptable useages. A 'bit perfect rip of a CD to PC' and transmission of a 'bit perfect', unmixed or tampered with signal from PC to DAC.

Yup that's pretty much it.

Thanks, I have learned something new and useful so today is a good day.

 

[PJPro]

Pete10:
BTW Volume control is possible in WASAPI too, in which case it is not bitperfect.

Is volume control possible? If it is, then the default setting for the WASAPI plugin in foobar2000 must be exclusive mode.....cos I can't change the volume on my PC once foobar2000 is running (Vista). Are you sure you've set it up right?

 

[PJPro]

Pete10:
Although sample _rate_ conversion SRC should be avoided, it is not true that windows always does it. If the only source is 44.1kHz/16bits Windows' kmixer will NOT resample (unless it knows that the audio device does not support this format, which is unlikely).

Volume control (ie less than 100%) is not SRC, but lowers the values of the (16bits) samples. This reduces the dynamic range and should probably be avoided also.

In general, both SRC and Volume control (or levelling) can work without a major sound quality effect (unless SR is very low, or volume is very low and than pumped up again by the amp): algorithms have good interpolation techniques. But as said, avoiding it is better.

I thought we had covered this before. There is a slight reduction in volume even when it is set to 100% resulting in less than bit perfect playback, even when only single source of audio is being mixed. Whether you can hear the difference or not is another matter.

 

[Anonymous]

Under Win7(32bits) Foobar WASAPI>USB DAC I can use the volume slider within foobar but indeed not in the volume mixer where foobar shows up when active with its own slider (moving has no effect). And it runs in exclusive mode. BTW, the default WASAPI setting of 1000ms buffer size works but in my system with some dropouts when accessing the source, perhaps tru a (sometimes busy) wireless connection. Unfortunately other buffer sizes lead to big problems and artifacts in playback.

About the 100% volume: there are some conflicting reports whether this is really 100%.

EDITED BY MODS: House Rules

Anyway MediaMonkey wave_out at 100% volume works ok for me, MM 4 will supposedly include WASAPI.

 

[Anonymous]

I'm not convinced by this bit-perfect business. If the same files are streamed down three different cables costing, say, £5, £50, £500 and each arrive as bit-perfect images of the original then they should all sound the same. However, they don't, at least according to my ears and many others on this forum, so how come they all sound or look different?

 

[The_Lhc]

Grottyash:I'm not convinced by this bit-perfect business. If the same files are streamed down three different cables costing, say, £5, £50, £500 and each arrive as bit-perfect images of the original then they should all sound the same. However, they don't, at least according to my ears and many others on this forum, so how come they all sound or look different?

You're missing the point, if the data is not the same once it reaches the end of a cable, then that's the cables fault (and a whole other argument that really, we DON'T need to have here! There's plenty of other threads that cover that).

The idea of bit-perfect is that it hasn't changed after it's ripped and that, in the case of playing from a PC, the PC doesn't change it BEFORE it goes down the cable.

 

[Anonymous]

No, as idc said " A 'bit perfect rip of a CD to PC' and transmission of a 'bit perfect', unmixed or tampered with signal from PC to DAC." It's the second part to which I'm referring. Surely the transmission is via a cable.

 

[The_Lhc]

Grottyash:No, as idc said " A 'bit perfect rip of a CD to PC' and transmission of a 'bit perfect', unmixed or tampered with signal from PC to DAC." It's the second part to which I'm referring. Surely the transmission is via a cable.

Yes but this thread has been focussing on how to stop the PC from changing the signal BEFORE it squirts it down the cable. If the cable itself is doing something (which as I said is an argument you're welcome to go and have elsewhere as this thread is specifically NOT a cable argument!) then there's nothing you can do about that on the PC itself.

Either way, surely you want to eliminate all possible sources of data corruption but your viewpoint seems to imply that you might as well not worry about how good the ripping is or whether the PC is changing the signal, which seems a little odd. By that token if it's all about the cable then who cares what CD player or pre-amp you buy as surely they can't overcome the limitations of your cables?

That doesn't seem entirely logical to me...

 

[Gerrardasnails]

the_lhc:
Grottyash:No, as idc said " A 'bit perfect rip of a CD to PC' and transmission of a 'bit perfect', unmixed or tampered with signal from PC to DAC." It's the second part to which I'm referring. Surely the transmission is via a cable.

Yes but this thread has been focussing on how to stop the PC from changing the signal BEFORE it squirts it down the cable. If the cable itself is doing something (which as I said is an argument you're welcome to go and have elsewhere as this thread is specifically NOT a cable argument!) then there's nothing you can do about that on the PC itself.

Either way, surely you want to eliminate all possible sources of data corruption but your viewpoint seems to imply that you might as well not worry about how good the ripping is or whether the PC is changing the signal, which seems a little odd. By that token if it's all about the cable then who cares what CD player or pre-amp you buy as surely they can't overcome the limitations of your cables?

That doesn't seem entirely logical to me...

I agree with you lhc.

 

[idc]

I was trying to find out what bit perfect meant when being used in the context of itunes, Foobar etc transmitting a music file's data to a DAC. There needs to be two different terms as you end up with a sentence 'I transmitted a bit perfect file imported into itunes off a CD which was not 100% bit perfect due to Windows Kmixer' and that makes sense! Bit perfect transmission should be called uncorrupted or un-mixed or similar.