# TiVo's two different audio settings?



## NoVa (Feb 26, 2006)

TiVo's (P4 in my case) two audio settings -
1) is classified 'Dolby Digital' 
2) is classified as 'Dolby Digital to PCM'.

Though - I am unsure what the difference is or when to use#1 is vs. #2?


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## steve614 (May 1, 2006)

It depends on what equipment you have hooked up to your Tivo.

Dolby Digital is usually 5.1 stereo surround (depends on the source).
When you have the Tivo set to 'Dolby Digital', it will pass the source audio signal through to the device(s) that it is connected to.
When you have the Tivo set to 'Dolby Digital to PCM', the Tivo down converts the audio to 2 channel stereo before it is passed on to the devices.


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## moyekj (Jan 24, 2006)

On a related note, if you are just using HDMI & TV speakers for audio, PCM may be a better choice. With the default Dolby output after using a trick play function such as 30 sec skip I noticed a brief audio dropout which got to be annoying. I discovered changing this setting to send PCM to TV fixed the problem of this brief audio dropout, and since I'm just using TV speakers for that location PCM is good enough.


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## NoVa (Feb 26, 2006)

steve614 said:


> It depends on what equipment you have hooked up to your Tivo.
> 
> Dolby Digital is usually 5.1 stereo surround (depends on the source).
> When you have the Tivo set to 'Dolby Digital', it will pass the source audio signal through to the device(s) that it is connected to.
> When you have the Tivo set to* 'Dolby Digital to PCM',* the Tivo down converts the audio to 2 channel stereo before it is passed on to the devices.


Thank you.

On latter - why would PCM be considered downconverting? I thought PCM processes audio signals that are passed through an audio system.

Are you actually saying that the TiVo compresses a source DD 5.1 signal to a stereo PCM track & then sends it out to whatever component can 'unzip' it ....& if a TV or receiver can't then it stays as 2-channel stereo?


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## NoVa (Feb 26, 2006)

moyekj said:


> On a related note, if you are just using HDMI & TV speakers for audio, PCM may be a better choice. With the default Dolby output after using a trick play function such as 30 sec skip I noticed a brief audio dropout which got to be annoying. I discovered changing this setting to send PCM to TV fixed the problem of this brief audio dropout, and since I'm just using TV speakers for that location PCM is good enough.


I am actually using HDMI to TV - for limiting AVReceiver usage & to get the TiVo sound effect. 

However, I am still interested in what the TiVo does to a signal when using PCM esp. when it comes out the other side to a TV or Receiver...


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## takeshi (Jul 22, 2010)

NoVa said:


> On latter - why would PCM be considered downconverting?


Steve isn't referring to PCM in general but specifically the Tivo's PCM conversion. IIRC there's nothing to decode and it's just stereo.


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## Ennui (Sep 2, 2008)

takeshi said:


> Steve isn't referring to PCM in general but specifically the Tivo's PCM conversion. IIRC there's nothing to decode and it's just stereo.


I have an old Bose 5.1 system fed by the optical out on the Premiere TiVo through a converter. When using Dolby out, I only get output on the front L-R speakers. Using PCM, I get output on all 5 speakers. FWIW


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## NoVa (Feb 26, 2006)

Ennui said:


> I have an old Bose 5.1 system fed by the optical out on the Premiere TiVo through a converter. When using Dolby out, I only get output on the front L-R speakers. Using PCM, I get output on all 5 speakers. FWIW


hmmm - if I interpret what you are saying - you are contradicting what Steve614 stated: that the optical *is *passing DD5.1 via optical to your converter & it's is lighting up all 5 speakers thru your converter (receiver)?


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## Ennui (Sep 2, 2008)

NoVa said:


> hmmm - if I interpret what you are saying - you are contradicting what Steve614 stated: that the optical *is *passing DD5.1 via optical to your converter & it's is lighting up all 5 speakers thru your converter (receiver)?


Yes, that is correct. The converter is an external device in the line to the Bose. I do not know the details. It is at least 5 years old.


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## moyekj (Jan 24, 2006)

PCM is Pulse Code Modulation and is uncompressed audio. In general you cannot assume PCM is inferior as it can spit out up to 8 channels of audio and much higher bit rates than Dolby Digital (being uncompressed it does need higher bit rates to begin with). I don't know exactly what TiVo outputs as PCM though but it sounds like it may be more than 2 channels. I think some audiofiles actually prefer to use PCM output from Blu Ray players for example.


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## waynomo (Nov 9, 2002)

moyekj said:


> PCM is Pulse Code Modulation and is uncompressed audio. In general you cannot assume PCM is inferior as it can spit out up to 8 channels of audio and much higher bit rates than Dolby Digital (being uncompressed it does need higher bit rates to begin with). I don't know exactly what TiVo outputs as PCM though but it sounds like it may be more than 2 channels. I think some audiofiles actually prefer to use PCM output from Blu Ray players for example.


:thumbup:

Most receivers should be able to decode PCM into 5.1 using Pro Logic. That being said, if you have a receiver that can do Dolby Digital, that should sound better.

I believe that that PCM is is encoding using an algorithm, and is decoded and makes some assumptions so is not coming out true 5.1. (disclaimer: it's been over 8 years since I seriously got into all that.)


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## Ennui (Sep 2, 2008)

waynomo said:


> :thumbup:
> 
> Most receivers should be able to decode PCM into 5.1 using Pro Logic. That being said, if you have a receiver that can do Dolby Digital, that should sound better.
> 
> I believe that that PCM is is encoding using an algorithm, and is decoded and makes some assumptions so is not coming out true 5.1. (disclaimer: it's been over 8 years since I seriously got into all that.)


Maybe it is the converter I have. In watching baseball games transmitted in 5.1, I do get the crowd noises in the rear speakers and the announcers in the front ones. There is no announcer voice in the rear.


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## NoVa (Feb 26, 2006)

waynomo said:


> :thumbup:
> 
> Most receivers should be able to decode PCM into 5.1 using Pro Logic. That being said, if you have a receiver that can do Dolby Digital, that should sound better.
> 
> I believe that that PCM is is encoding using an algorithm, and is decoded and makes some assumptions so is not coming out true 5.1. (disclaimer: it's been over 8 years since I seriously got into all that.)


The question for me is: does the TiVo do any encoding of the source track to 2Chnl Stereo -'downconvert' - before passing it out as PCM?

My guess is no.
It's still strictly sourced based & if the signal comes over as 5.1, then TiVo PCM it as is & it's up to the receiver to decode it. Right?


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## moyekj (Jan 24, 2006)

NoVa said:


> The question for me is: does the TiVo do any encoding of the source track to 2Chnl Stereo -'downconvert' - before passing it out as PCM?
> 
> My guess is no.
> It's still strictly sourced based & if the signal comes over as 5.1, then TiVo PCM it as is & it's up to the receiver to decode it. Right?


 That would be my assumption as well, but I don't know if it's true or not.


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## Ennui (Sep 2, 2008)

moyekj said:


> That would be my assumption as well, but I don't know if it's true or not.


I found the sales sheet for the converter from Audio Authority. I have the

Model 977RPO
Digital Optical to Digital Coaxial Converter

http://www.audioauthority.com/downloads/literature/977_ci_focus-sheet-printable_2008-8.pdf

FYI.


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## jtso (Oct 2, 2009)

moyekj said:


> PCM is Pulse Code Modulation and is uncompressed audio. In general you cannot assume PCM is inferior as it can spit out up to 8 channels of audio and much higher bit rates than Dolby Digital (being uncompressed it does need higher bit rates to begin with). I don't know exactly what TiVo outputs as PCM though but it sounds like it may be more than 2 channels. I think some audiofiles actually prefer to use PCM output from Blu Ray players for example.


Thanks very much for this thread, and it solved the problem with the split second audio dropout when coming out of trick play, such as fast forwarding. I have the TiVo (2-tuner Premiere) connected to a receiver via HDMI.

When I switched the setting on the TiVo from Dolby to PCM, at first I only got 2-channel stereo. I then changed a setting on the receiver to "Pro Logic", and 5.1 audio came out. I do believe it sounds a bit more trebly this way, and it helps me hear dialog a little better, although that might just be my hearing going bad.


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## moyekj (Jan 24, 2006)

From Premiere User Guide manual I see this confirming that PCM for series 4 units does indeed down-convert to 2 channels:


tivo manual said:


> When selecting the Dolby Digital to PCM setting, the audio signal will be downmixed from Dolby Digital 5.1 to 2-channel PCM.


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## Ennui (Sep 2, 2008)

moyekj said:


> From Premiere User Guide manual I see this confirming that PCM for series 4 units does indeed down-convert to 2 channels:


I wonder if this also covers the optical out...I am watching the All Star game now and there is definitely crowd noises only in rear speakers and announcers in front center speaker.


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## evanborkow (Mar 17, 2008)

Ennui said:


> I wonder if this also covers the optical out...I am watching the All Star game now and there is definitely crowd noises only in rear speakers and announcers in front center speaker.


You AVR may be simulating surround sound from the 2 channel source.


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