Friday, July 21, 2006

An Investigation of using "You Tube" to stream online video content through to Blogger

Blogger itself does not allow the user to upload video content, only still images. By using "You Tube", - http://www.youtube.com it is possible to stream video onto Blogger.

The following is an example of this (courtesy of Simon Perkins, http://en.wikipedia.org/wiki/A_Little_Death:_A_Modern_Day_Fairytale).





Thursday, July 20, 2006

ProTools LE and Reason



A recent training session on ProTools was attended and it was observed that using ProTools LE internally "rewired" to Propellerhead's Reason is a really neat all in one solution for music production and editing. Purchasing a Digidesign MBox 2, which ships with ProTools LE, together with Reason is extremely good value (approx. £450), especially for teaching purposes. By creating an Aux. Input track within the ProTools environment enables the Reason instrument to be loaded as an Insert and effectively triggered via a MIDI track. If a stereo track is created, Reason's STEREO output is routed into ProTools, meaning that all individual instruments are sub-mixed within Reason. If a mono track is created, all of Reason's individual outputs (upto 64) can be routed individually into ProTools for further processing.

Reason is also good for teaching audio wiring and routing through its virtual patching system.

Sennheiser MKH-416


A Sennheiser MKH-416 microphone has just been ordered. The aim is to carry out some simple tests and comparisons with the Sennheiser K66 microphone and the results will be posted on this Blog soon. Audio comparisons have already been listened to through the DV Freelancer website (www.dvfreelancer.com) so it is already acknowledged how much better the 416 sounds, however, it will be most interesting to carry out further tests.

Thursday, July 13, 2006

Shotgun Mics

A fantastic website has just been discovered discussing and demonstrated/comparing a range of different microphones designed for sound for picture. The URL is: http://www.dvfreelancer.com/articles/shotgun_shootout.html

I have only got experience of using the Sennheiser ME66 / K6 shotgun microphone and have never been particularly impressed with it. It sounds incredibly "thin" and tinny even when used up close, so using it from a fair distance to keep it out of shot produces even thinner results. It appears that either the Audio Technica AT4073A (current price approx. £719 at Digital Village) or the Sennheiser MKH-416 (current price approx. £799 at Digital Village) give far far superior results as the link above demonstrates.

Tuesday, July 11, 2006

What's the best way to record?

A recent task was carried out to try and answer the following question:
What is the best way to record - low gain setting to minimise hiss from the pre-amp and to provide a large amount of headroom? Or, a higher gain setting to give a higher signal level, less headroom and higher noise floor?

The following equipment was used:
Laptop running Sony Soundforge 7
Edirol UA25 USB Powered 24bit/96kHz Audio Interface
Sennheiser K6 Shotgun Condenser Microphone
Beyer DT100 Headphones
Duvet to help minimise reflections and "room noise"

With Soundforge set to record at standard CD-A quality (i.e. fs=44.1kHz and bit depth = 16), the microphone was connected to the audio interface and Phantom Power was switched on (on the Edirol interface). The microphone and subject were placed under a duvet(!) to help reduce background noise and reflections so that the noise floor was as low as possible; the subject was approx. 30cm from the microphone. With Soundforge recording, the gain setting on the audio interface was firstly set to its minimum position and a count was carried out at normal conversation level, then the same was carried out for a gain of approx. 9 o'clock, 12 o'clock (where clipping started to occur) and finally 3 o'clock which caused severe clipping. Each recording was then analysed (using the Statistics tool) for the peak sample value, RMS level (important as the human hear responds to average level, not peak) and approximate noise floor level (as observed on the dBFS meters) for both non-normalised and normalised versions.

The results are were as follows:
Gain of zero (minimum position)
non-normalised peak sample value: -24.07dBFS
non-normalised RMS value: -39.09dB
non-normalised noise floor level: -54dBFS (approx.)

normalised peak sample value: 0dBFS
normalised RMS value: -16.97dB
normalised noise floor level: -37dBFS (approx.)

Gain set to 9 o'clock position
non-normalised peak sample value: -8.3dBFS
non-normalised RMS value: -27.62dB
non-normalised noise floor level: -54dBFS

normalised peak sample value: 0dBFS
normalised RMS value: -20.33dB
normalised noise floor level: -47dBFS

Gain set to 12 o'clock position
non-normalised peak sample value: -1.24dBFS
non-normalised RMS value: -18.2dB
non-normalised noise floor level: -40dBFS

normalised peak sample value: 0dBFS
normalised RMS value: -17.81dB
normalised noise floor level: -40dBFS

Observations and Conclusions
It must be appreciated that some of these results are only approximate observations. In brief, it can be seen that the best compromise appears to be with the gain setting (in this case) to the 9 o'clock position which gave a good amount of headroom (peak, non-normalised value of -8.3dBFS) with a low level noise floor. Normalising these values gives a S/N ratio of approx. 47dB which isn't too bad considering the acoustic environment of the space used. It is also interesting to note that at a glance, the results aren't that much better than the results for the previous post entitled Quick VX2000 Audio Test Results, however, audibly the recordings were far far superior - much cleaner and with far less noise. This backs up the advantage of using separate high quality recording devices when recording sound for picture.

Quick VX2000 Audio Test Results

Further to the previous post on the audio performance of the VX2000, a quick and simple test was carried out to establish some data. A Sennheiser K6 microphone was connected to the camera (battery powered obviously as the VX provides no phantom power option), and held approx. 30cm from the subject. The gain on the camera was set to manual mode and set to its minimum position. Then, with the camera set to record, a simple count, at normal conversation level, was spoken into the microphone. This was repeated with the manual gain set to 2 clicks up, 4 clicks up, 6 clicks up and finally 8 clicks up, which resulted in clipping (i.e. hitting or surpassing the 0dBFS level on the camera).

The camera was then connected to a laptop PC via Firewire and the audio "footage" was captured into Premiere Pro. It was obviously important to use a digital transfer into the PC so as not to add any gain or attenuation to the signal. The audio was then exported as a wave file using standard DV settings (fs=48kHz and bit depth = 16) and then loaded into Sony Soundforge 7. The signal was monitored from the PC on a pair of Beyer DT100 headphones connected to an Edirol UA25 audio interface and immediately upon playback it was noticeable just how much hiss there was on the recording, even with the gain in its minimum position. The files were approximately analysed by observing the peak levels on the dBFS meters within Soundforge for both the noise floor and for the recorded speech for each of the gain settings; the results are shown here:

0 clicks:
Noise floor: approx. -49.5dBFS
Peak of recording: approx. -11dBFS
Approximate S/N Ratio: 38.5dB

2 clicks:
Noise floor: approx. -43.8dBFS
Peak of recording: approx. -11dBFS
Approximate S/N Ratio: 31.8dB

4 clicks:
Noise floor: approx. -40.6dBFS
Peak of recording: approx. -7.1dBFS
Approximate S/N Ratio: 33.5dB

6 clicks:
Noise floor: approx. -36.8dBFS
Peak of recording: approx. -2.1dBFS
Approximate S/N Ratio: 34.7dB

8 clicks:
Noise floor: approx. -39dBFS
Peak of recording: approx. 0dBFS (and above)
Approximate S/N Ratio: 39dB

Observations and Conclusions:
It is important to note that these are approximate measurements and that the room used to carry out the recordings in was not acoustically treated in any way. Therefore, the background noise level was fairly high and factors such as traffic noise from the nearby road needs to be taken into account. However, audibly, the noise floor was very high on all settings resulting in a poor S/N ratio. There was also some occasional low level clicks and pops throughout the recordings too. It is also interesting to note that the approximate S/N Ratio hardly changed regardless of manual gain position on the camera, therefore one would suggest that when using this camera to record audio with, perhaps a low gain setting is equally as good as a high one? Peaking a low as -11dBFS is fine when recording DV audio (as already discussed elsewhere, some texts state that DV audio can peak as low as -20dBFS to allow for 20dB headroom), and the audio file could always be normalised to bring the peak level up in the edit any way. Whatever the gain position, the recording quality is compromised by the high noise levels which isn't masked particularly well by the signal.

Some further articles of interest are:
http://www.dvfreelancer.com/articles/vx2000.html

http://www.gregjwinter.com/compare.htm

Thursday, July 06, 2006

Peak audio levels in DV?

Coming from an audio background where it is the norm to try and master recordings as close to 0dBFS as possible, it is interesting to note that Young, R (2006) "Easy Guide to Final Cut Pro 5" states that DV audio should peak at -12dBFS?

This is an interesting issue as in a previous post it was discussed that the 0dB indicator on a field mixer (in this case the Sound Devices 302) should correspond to -20dBFS on the DV camera, thus allowing for 20dB of headroom for peaks. However, if DV audio should really only peak at -12dBFS, this really only provides for 8dB of headroom. In practice, probably what would happen is that the full 20dB of headroom was made availale during recording and then compressed / limited down to peaks at -12dBFS during the post production phase.

Wednesday, July 05, 2006

Dither

Two important facts about applying dither to a signal prior to it entering the ADC (analogue to digital converter) were discovered recently.

Firstly, the signal to noise (or more accurately, signal to dither ratio) reduces by approximately 5dB, giving a dynamic range of 91dB for a 16 bit system.

Secondly, the perceived dynamic range can actually exceed the theoretical as stated aboved and can actually be more like 115dB for a 16 bit system. This is apparently because low level signal levels can actually be heard below the level of the noise applied? More info in Katz, R (2002) "Mastering Audio: The Art and the Science".

Portable Vocal Booth

Portable Vocal Booth known as the "Reflexion Filter" from Sound Engineering (SE) - www.seelectronics.com has been observed in the July 2006 issue of Sound on Sound. This appears to be an excellent and innovative idea which supposedly allows much cleaner and "drier" sounding recordings to be obtained in acoustically untreated spaces. With budget studios becoming ever more popular this offers a very cheap solution (RRP = £229.00) for reducing reflections from room surfaces which often add unnecessary colour to recordings. It is also not only limited to vocal recording.

Audio Performance of Sony VX2000 Camera

After using the Sony VX2000 Mini DV camera a while back, it became apparent on just how poor the device was for audio. Not only does the VX2000 merely have a single stereo 3.5mm mini jack for its mic input (instead of superior XLR connectors), it provides no phantom powering for attached condenser microphones either. The only way to use microphones requiring power of some kind is to battery power them and to use adaptor cables to convert the XLR to said mini jack.

Aside from the connectivity issues of the camera, its actual audio performance is well below par too. Manual gain mode is available (but only for both channels simultaneously) but engaging this causes incredible amounts of hiss (assumed to be from the front end pre-amp). A test was carried out using Soundforge and what was immediately noticeable was just how high the noise floor was. The camera is capable of either 12 or 16-bit recording resolutions (giving theoretical dynamic ranges of 72dB and 96dB respectively assuming no dither applied), but this is totally pointless given just how noisy the front end is. The test will be carried out again soon for the purposes of this blog and the results will be posted but a noise floor higher than -40dBFS springs to mind. Why therefore bother using 16 bit resolution when, in theory, an 8 bit resolution would be more than adequate (48dB theoretical dynamic range).

To help overcome this problem, on a recent video project, a separate audio device (in this case a laptop running Soundforge plugged into an Edirol UA-25 soundcard) was used to capture the audio. Not only did this give far far superior results audibly, it also added the benefit of two separate XLR inputs each with manual gain control, +48V phantom power and 24 bit, 96kHz capabilities. As Soundforge was used, the audio was recorded as standard wave file formats which could easily be dragged into the NLE (Sony Vegas) and lined up with the video, using the onboard camera sound as a reference.

Glensound - http://www.glensound.com/ manufacture a box called the GSTN-1 which connects to the VX2000 and provides a better front end plus XLR connections. They also manufacture a version to be used in conjunction with a modified (by the BBC) VX2000 which performs even better.

It is hoped that very soon, one of the new Sony HD cameras with onboard XLR connections will be investigated for its audio performance.

Calibration of Field Mixer to DV Camera

Recently I have been reviewing what field mixers are available to use in conjunction with DV cameras, and more importantly the need for signal calibration between devices. The Sound Devices 302 has a bar graph display peaking at +20dBu (approx. 7.75Vrms) thus allowing for the monitoring of extremely high signal levels. One would assume that during line up, the inputs on the DV camera would be adjusted so that the standard 1kHz tone @ 0dB (= 0dBu and not the more common +4dBu) caused a reading of 0dBFS on the DV camera's meter. However, this obviously allows for absolutely zero headroom on the camera for any sudden peaks which exceed 0dB on the field mixer. Therefore, the 302 user's manual recommends setting the input levels on the DV camera so that the meter registers -20dBFS for the 0dB line up tone thus allowing for the 20dB headroom to be accommodated by the camera.

The bar graph meter on the 302 turns orange at 0dB (i.e. -20dBFS on the camera) and then turns red at +8dB (i.e -12dBFS on the camera).

HD Audio

Why is there a requirement for HD audio (24 bit resolution and higher sampling rates?). I have been reviewing Katz, B (2002) "Mastering Audio - The Art and the Science" recently which discusses this very issue. Katz questions why there is a race to create the hottest sounding album with very minimal dynamic range? The added benefit of increasing the number of bits from 16 to 24 is an increase in the "theoretical" dynamic range by 48dB. With this additional headroom, why do we still squash eveything down into almost square waves during the mastering process? With the advent of DVD-Audio for example, will mastering engineers still try to squeeze the dynamic range into almost non-existence?

It is interesting to note Katz's argument stating that a 16 bit recording effectively sits within the range -144dB to -48dB (96dB dynamic range) thus meaning that even if the peak sample only hit -48dBFS (under "full scale") in a 24bit system, the same effective recording could be carried out. I always aim to hit as near to 0dBFS during the recording process as possible (regardless of resolution used), however, from now I on I plan to start leaving more headroom available when recording at higher resolutions.